Title: Hawkins Electrical Guide Vol. 8 (of 10) - A Progressive Course of Study for Engineers, Electricians, - Students, and Those Desiring to Acquire a Working Knowledge - of Electricity and Its Applications
Author: Hawkins, N. (Nehemiah)
Language: English
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Transcriber's Notes:

  Underscores "_" before and after a word or phrase indicate _italics_
    in the original text.

  Equal signs "=" before and after a word or phrase indicate =bold=
    in the original text.

  Small capitals have been converted to SOLID capitals.

  Illustrations have been moved so they do not break up paragraphs.

  Misprints in the table SAVING DUE TO HEATING THE FEED WATER, Pg. 1936
    have been corrected, they are:

         Init. Temp.     Pressure     Old Value      New Value
            130            40            .0954          .0934
            200            40            .0900          .0999
            210            40            .1000          .1010
            230           100            .0117          .1012

 In the original text, there are two Fig. 2769's and two Fig. 2770's.
 The second of each has had an "a" suffix added, i.e. 2769a and 2770a.

 On line 7397 the word "impedence" was corrected to "impedance".

 Superscripts are shown as ^{d} and subscripts are shown as _{d}, where
 "d" is an integer.

 Inconsistent spelling and hyphenation has been left as in the original.



       THE THOUGHT IS IN THE QUESTION
      THE INFORMATION IS IN THE ANSWER

    HAWKINS ELECTRICAL GUIDE NUMBER EIGHT

     QUESTIONS ANSWERS & ILLUSTRATIONS

  A PROGRESSIVE COURSE OF STUDY FOR ENGINEERS,
  ELECTRICIANS, STUDENTS AND THOSE DESIRING TO
        ACQUIRE A WORKING KNOWLEDGE OF

       ELECTRICITY AND ITS APPLICATIONS

   A PRACTICAL TREATISE by HAWKINS AND STAFF

   THEO AUDEL & CO. 72 FIFTH AVE. NEW YORK.

   COPYRIGHTED, 1915, BY THEO. AUDEL & CO.,

               NEW YORK.
          Printed in the United States.



                   TABLE OF CONTENTS
                      GUIDE No. 8


  =WAVE FORM MEASUREMENT=                            1,839 to 1,868

   Importance of wave form measurement--=methods=:
   step by step; constantly recording--=classes of
   apparatus=: wave indication; _oscillographs_--=step
   by step methods=--Joubert's; four part commutator;
   modified four part commutator; ballistic galvanometer;
   zero; Hospitalier ondograph--=constantly recording
   methods=: cathode ray; glow light; moving iron; moving
   coil; hot wire--=oscillographs=--moving coil type;
   construction and operation; production of the time scale;
   oscillograms--falling plate camera; its use.

  =SWITCHBOARDS=                                     1,869 to 1,884

   =General principles=: diagram--small plant a.c.
   switchboard--=switchboard panels=; =generator
   panel=; diagram of connections--simple method of
   determining bus bar capacity--feeder panel--diagrams of
   connection for two phase and three phase installations.

  =ALTERNATING CURRENT WIRING=                       1,885 to 1,914

   Effects to be considered in making
   calculations--=induction=; self- and mutual; mutual
   induction, how caused--=transpositions=--inductance
   per mile of three phase circuit, table--=capacity=;
   table--=frequency--skin effect=; calculation;
   table--=corona effect=; its manifestation;
   critical voltage; spacing of wires--=resistance of
   wires--impedance--power factor=; apparent current;
   usual power factors encountered; example--=wire
   calculations--sizes of wire--table of the property of
   copper wire--drop=; example--current--example covering
   horse power, watts, apparent load, current, size of wire,
   drop, voltage at the alternator, and electrical horse power.

  =POWER STATIONS=                                   1,915 to 1,988

   Classification--=central stations=; types: a.c.,
   d.c., and a.c. and d.c.; reciprocating engine vs.
   turbine--=location of central stations=; price of
   land; trouble after erection; water supply; service
   requiring direct current--=size of plant=; nature
   of load; peak load; load factor; machinery required;
   example; factors of evaporation; grate surface per
   horse power--=general arrangement of station=;
   belt drive with counter shaft; desirable features of
   belt drive; conditions, suitable for counter shaft
   drive; location of engine and boilers; the steam pipe;
   piping between engine and condenser; number and type
   of engine; superheated steam; switchboard location;
   individual belt drive; direct drive--=station
   construction=--=foundations=--=walls=--
   =roofs=--=floors=--=chimneys=;
   cost of chimneys and mechanical draft; high chimneys
   ill advised--=steam turbine=; types: impulse
   and reaction; why high vacuum is necessary; the
   working pressure--=hydro-electric plants=--water
   turbines; types: impulse, reaction--=isolated
   plants=--=sub-stations=; arrangement; three phase
   installations; reactance coils in sub-stations; portable
   sub-stations.

  =MANAGEMENT=                                       1,989 to 2,114

   The term "management"--=selection=; general
   considerations--=selection of generators=;
   efficiency of generators; size and number;
   regulation--=installation=; precautions;
   handling of armatures; assembling a machine; speed
   of generators; calculation of pulley sizes; gear
   wheels--=belts=; various belt drives; horse
   power transmitted by belts; velocity of belt; endless
   belts--=switchboards=; essential points of difference
   between single phase and three phase switchboard wiring;
   assembling a switchboard; usual equipment.

   =Operation of Alternators--alternators in parallel=;
   synchronizing; lamp methods; action of amortisseur winding;
   synchronizing three phase alternators; disadvantage of
   lamp method--=cutting out alternator=; precautions;
   hunting--=alternators in series=.

   =Transformers=; selection; efficiency; kind of oil
   used; detection of moisture; drying oil; regulation;
   transformers in parallel; polarity test--=motor
   generators=; various types and conditions requiring
   same--=dynamotors=; precautions--=rotary
   converters=; objections to single phase type; operation
   when driven by direct current, by alternating current; most
   troublesome part; efficiency; overload; starting; starting
   current.

   =Electrical measuring instruments=; location;
   readings; station voltmeters; points relating to
   ammeters; attention necessary; usual remedies to correct
   voltmeter--=how to test generators=; commercial
   efficiency; various tests.

   =Station Testing:= resistance measurement by "drop"
   method--methods of connecting ammeter voltmeter and
   wattmeter for measurement of power--=motor testing:=
   single phase motor--three phase motor, voltmeter and
   ammeter method; two wattmeter method; polyphase wattmeter
   method; one wattmeter method; one wattmeter and Y box
   method--three phase motor with neutral brought out; single
   wattmeter method--temperature test, three phase induction
   motor--=three phase alternator testing:= excitation
   or magnetization curve test--synchronous impedance
   test--load test--three phase alternator or synchronous
   motor temperature test--=direct current motor= or
   =generator testing:= magnetization curve--(shunt)
   external characteristic--direct current motor testing;
   load and speed tests--temperature test, "loading back"
   method--=compound dynamo testing=: external
   characteristic, adjustable load--=transformer testing=:
   external characteristic, adjustable load--=transformer
   testing=: core loss and leakage or exciting current
   test--copper loss--copper loss by wattmeter measurement
   and impedance--temperature--insulation--internal
   insulation--insulation resistance--polarity--winding
   or ratio tests.



CHAPTER LXIII

WAVE FORM MEASUREMENT


The great importance of the wave form in alternating current work
is never denied, though it has sometimes been overlooked. The
application of large gas engines to the driving of alternators
operated in parallel requires an accurate knowledge of the wave form,
and a close conformation to a sine wave if parallel operation is
to be satisfactory. It is also important that the fluctuations in
magnetism of the field poles should be known, especially if solid
steel pole faces be used.

     If an alternator armature winding be connected in delta, the
   presence of a third harmonic becomes objectionable, as it gives
   rise to circulating currents in the winding itself, which increase
   the heating and lowers the efficiency of the machine.

     That the importance of having a good wave form is being
   realized, is proved by the increasing prevalence in alternator
   specifications of a clause specifying the maximum divergence
   allowable from a true sine wave. It is however perhaps not always
   realized that an alternator which gives a good pressure wave on
   no load may give a very bad one under certain loads, and the
   ability of the machine to maintain a good wave form under severe
   conditions of load is a better criterion of its good design than
   is the shape of its wave at no load.

     The question of wave form is of special interest to the power
   station engineer. Upon it depends the answer to the questions:
   whether he may ground his neutral wires without getting large
   circulating currents; whether he may safely run any combination
   of his alternators in parallel; whether the constants of his
   distributing circuit are of an order liable to cause dangerous
   voltage surges due to resonance with the harmonics of his
   pressure wave; what stresses he is getting in his insulation due
   to voltage surges when switching on or off, etc. It has been
   shown by Rossler and Welding that the luminous efficiency of the
   alternating current arc may be 44 per cent. higher with a flat
   topped than with a peaked pressure wave, while on the other hand
   it is well known that transformers are more efficient on a peaked
   wave. Also the accuracy of many alternating current instruments
   depends upon the wave shape.

     In making insulation breakdown tests on cables, insulators, or
   machinery, large errors may be introduced unless the wave form at
   the time of the test be known. It is not sufficient even to know
   that the testing alternator gives a close approximation to a sine
   wave at no load; since if the capacity current of the apparatus
   under test be moderately large compared with the full load current
   of the testing alternator, the charging current taken may be
   sufficient to distort the wave form considerably, thus giving
   wrong results to the disadvantage of either the manufacturer or
   purchaser.

[Illustration: FIG. 2,583.--General Electric simultaneous record of
three waves with common zero.]

The desirability of a complete knowledge of the manner in which the
pressure and current varies during the cycle, has resulted in various
methods and apparatus being devised for obtaining this knowledge.
The apparatus in use for such purpose may be divided into two general
classes,

  1. Wave indicators;
  2. Oscillographs.

and the methods employed with these two species of apparatus may be
described respectively as,

  1. Step by step;
  2. Constantly recording.

that is to say, in the first instance, a number of instantaneous
values are obtained at various points of the cycle, which are plotted
and a curve traced through the several points thus obtained. A
constantly recording method is one in which an infinite number of
values are determined and recorded by the machine, thus giving a
complete record of the cycle, leaving no portion of the wave to be
filled in.

[Illustration: FIG. 2,584.--General Electric simultaneous record of
three waves with separate zeros.]

[Illustration: Figs. 2,585 and 2,586.--Oscillograms (from paper by
Morris and Catterson-Smith, Proc. I. E. E., Vol. XXXIII, page 1,023),
showing _how the current varies_ =in one of the armature coils of
a direct current motor=. Fig. 2,585 was obtained with the brushes
in the neutral position, and fig. 2,586 with the brushes shifted
forward.]


The various methods of determining the wave form may be further
classified as:

                  { Joubert's method;
                  { Four part commutator method;
                  { Modified four part commutator method;
  1. Step by step { Ballistic galvanometer method;
                  { Zero method;
                  { By Hospitalier ondograph.

[Illustration: FIG. 2,587.--=Oscillogram= by Bailey and Cleghorne
(Proc. I.E.E., Vol. XXXVIII), =showing= _the sparking pressure or
pressure between the brush and the commutator segment at the moment
of separation_. The waves fall into groups of three owing to the fact
that there were three armature coils in each slot.]

                                                     { cathode ray;
                          { by use of various types  { glow light;
  2. constantly recording { of =oscillograph=,       { moving iron;
                          { such as                  { moving coil;
                                                     { hot wire.


[Illustration: FIG. 2,588.--Various wave forms. The sine wave
represents a current or pressure which varies according to the sine
law. A distorted wave is due to the properties of the circuit, for
instance, the effect of hysteresis in an iron core introduced into a
coil is to distort the current wave by adding harmonics so that the
ascending and descending portions may not be symmetrical. A peaked
wave has a large maximum as compared with its virtual value. A peaked
wave is produced by a machine with concentrated winding.]

=Joubert's Method.=--The apparatus required for determining the
wave form by this step by step method, consists of a galvanometer,
condenser, two, two way switches, resistance and adjustable contact
maker, as shown in fig. =2,589=.

     The contact maker is attached to the alternator shaft so that
   it will rotate synchronously with the latter. By means of the
   adjustable contact, the instant of "making" that is, of "closing"
   the testing circuit may be varied, and the angular position of the
   armature, at which the testing circuit is closed, determined from
   the scale, which is divided into degrees.

     A resistance is placed in series with one of the alternator
   leads, such that the drop across it, gives sufficient pressure for
   testing.

=Ques. Describe the method of making the test.=

[Illustration: FIG. 2,589.--Diagram illustrating Joubert's =step by
step method= of wave form measurement.]

Ans. For current wave measurement switch No. 1 is placed on contact
F, and for pressure wave measurement, on contact G, switch No. 2 is
now turned to M and the drop across the resistance (assuming switch
No. 1 to be turned to contact F) measured by charging the condenser,
and then discharging it through the galvanometer by turning the
switch to S. This is repeated for a number of positions of the
contact maker, noting each time the galvanometer reading and position
of the contact maker. By plotting the positions of contact maker as
abscissæ, and the galvanometer readings as ordinates, the curve drawn
through them will represent the wave form.

[Illustration: FIG. 2,590.--=Four part commutator method= of wave
form measurement. The contact device consists of two slip rings and
a four part commutator. One slip ring is connected to one terminal
of the source, the other to the voltmeter, and the commutator to the
condenser. By adjusting R when a known direct current pressure is
impressed across the terminals, the voltmeter can be rendered direct
reading.]

[Illustration: FIG. 2,591.--=Modified four part commutator method=
of wave form measurement (Duncan's modification). By this method
one contact maker can be used for any number of waves having the
same frequency. Electro-dynamometers are used and the connections
are made as here shown. The moving coils are connected in series to
the contact maker, and the fixed coils are connected to the various
sources to be investigated, then the deflection will be steady and
by calibration with direct current can be made to read directly in
volts.]


     The apparatus is calibrated by passing a known constant current
   through the resistance.

[Illustration: FIG. 2,592.--Diagram illustrating the =ballistic
galvanometer method= of wave form measurement. =The test may be made=
as described in the accompanying text, or in case the contact breaker
is belted instead of attached rigidly to the shaft, it could be
arranged to run slightly out of synchronism, then by taking readings
at regular intervals, points will be obtained along the curve without
moving the contact breaker. If this method be used, a non-adjustable
contact breaker suffices. =In arranging the belt drive= so as to run
slightly out of synchronism, if the pulleys be of the same size, the
desired result is obtained by pasting a thin strip of paper around
the face of one of the pulleys thus altering the velocity ratio of
the drive slightly from unity.]

=Ballistic Galvanometer Method.=--This method, which is due to
Kubber, employs a _contact breaker_ instead of a _contact maker_.
The distinction between these two devices should be noted: A contact
maker keeps the circuit _closed_ during each revolution for a short
interval only, whereas, a contact breaker keeps the circuit _open_
for a short interval only.

     Fig. 2,592, shows the necessary apparatus and connections for
   applying the ballistic galvanometer method. The contact breaker
   consists of a commutator having an ebonite or insulating segment
   and two brushes.

     _In operation_ the contact breaker keeps the circuit closed
   during all of each revolution, except the brief interval in which
   the brushes pass over the ebonite segment.

     The contact breaker is adjustable and has a scale enabling its
   various positions of adjustment to be noted.

=Ques. Describe the test.=

[Illustration: FIGS.. 2,593 and 2,594.--=Two curves= _representing
pressure and current respectively of a rotary converter._ Fig. 2,593,
pressure wave V, fig. 2,594 current wave C. These waves were obtained
from a converter which was being driven by an alternator by means of
an independent motor. The rotary converter was supplying idle current
to some unloaded transformers and the ripples clearly visible in the
pressure wave V, correspond to the number of teeth in the armature of
the rotary converter.]

Ans. The contact breaker is placed in successive positions and
galvanometer readings taken, the switch being turned to F, fig.
2,592, in measuring the current wave, and to G in measuring the
pressure wave. The results thus obtained are plotted giving
respectively current and pressure waves.

=Ques. How is the apparatus calibrated?=

Ans. By sending a constant current of known value through the
resistance R.

=Zero Method.=--In electrical measurements, a zero method is one _in
which the arrangement of the testing devices is such that the value
of the quantity being measured is shown when the galvanometer needle
points to_ =zero=.

In the zero method either a contact maker or contact breaker may be
used in connection with a galvanometer and slide wire bridge, as
shown in figs. 2,595 and 2,596.

[Illustration: FIG. 2,595.--Diagram illustrating zero method of wave
measurement with _contact_ =maker=. The voltage of the battery must
be at least as great as the maximum pressure to be measured and must
be kept constant.]

=Ques. What capacity of battery should be used?=

Ans. Its voltage should be as great as the maximum pressure to be
measured.

=Ques. What necessary condition must be maintained in the battery?=

Ans. Its pressure must be kept constant.

=Ques. How are instantaneous values measured?=

Ans. The bridge contact A is adjusted till the galvanometer shows no
deflection, then the length AS is a measure of the pressure.

     The drop between these points can be directly measured with a
   voltmeter if desired.

=Ques. How did Mershon modify the test?=

Ans. He used a telephone instead of the galvanometer to determine the
correct placement of the bridge contact A.

[Illustration: FIG. 2,596.--Diagram illustrating zero method of wave
measurement with _contact_ =breaker=. The voltage of the battery must
be at least as great as the maximum pressure to be measured and must
be kept constant.]

=Ques. How can the instantaneous values be recorded?=

Ans. By attaching to the contact A, a pencil controlled by an
electro-magnet arranged to strike a revolving paper card at the
instant of no deflection, the paper being carried on a drum.

=Hospitalier Ondograph.=--The device known by this name is a
development of the Joubert step by step method of wave form
measurement, that is to say, the principle on which its =action is
based=, consists in _automatically charging a condenser from each
100th wave, and discharging it through a recording galvanometer, each
successive charge of the condenser being automatically taken from a
point a little farther along the wave._

[Illustration: FIG. 2,597.--Diagram of Hospitalier ondograph showing
mechanism and connections. It represents a development of Joubert's
step by step method of wave form measurement.]

     As shown in the diagram, fig. 2,597, the ondograph consists of
   a synchronous motor A, operated from the source of the wave form
   to be measured, connected by gears B to a commutator D, in such a
   manner that while the motor makes a certain number of revolutions,
   the commutator makes a like number diminished by unity; that is to
   say, if the speed of the motor be 900 revolutions per minute, the
   commutator will have a speed of 899.

     The commutator has three contacts, arranged to automatically
   charge the condenser _cc'_ from the line, and discharge it through
   the galvanometer E, the deflection of which will be proportional
   to the pressure at any particular instant when contact is made.

     In fig. 2,597, GG' are the motor terminals, HH' are connected to
   the condenser _cc'_ through a resistance (to prevent sparking at
   the commutator) and I, I' are the connections to the service to be
   measured.

     A permanent magnet type of recording galvanometer is employed.
   Its moving coil E receives the discharges of the condenser in
   rapid succession and turns slowly from one side to the other.

[Illustration: FIG. 2,598.--View of Hospitalier ondograph. =In
operation=, a long pivoted pointer carrying a pen and actuated by
electro-magnets, records on a revolving drum a wave form representing
the alternating current, pressure or current wave.]

     The movable part operates a long needle (separately mounted)
   carrying a pen F, which traces the curve on the rotating cylinder
   C. This cylinder is geared to the synchronous motor to run at such
   a speed as to register three complete waves upon its circumference.

     By substituting an electromagnetic galvanometer for the
   permanent magnet galvanometer, and by using the magnet coils as
   current coils and the moving coil as the volt coil, the instrument
   can be made to draw watt curves. Fig. 2,598 shows the general
   appearance of the ondograph.

=Cathode Ray Oscillograph.=--This type of apparatus for measuring
wave form was devised by Braun, and consists of a cathode ray tube
having a fluorescent screen at one end, a small diaphragm with a
hole in it at its middle, and two coils of a few turns each, placed
outside it at right angles to one another. These coils carry currents
_proportional to the_ =pressure= _and_ =current= _respectively_ of
the circuit under observation.

[Illustration: FIG. 2,599.--General Electric =moving coil
oscillograph= complete =with tracing table=. The tracing table is
employed for observing the waves, and by using a piece of transparent
paper, the waves under observation appear as a continuous band of
light which can be traced, thus making a permanent record. This is
not, however, to be regarded as a recording attachment, and can not
be used where instantaneous phenomena are being investigated. =The
synchronous motor= for operating the synchronous mirror in connection
with tracing and viewing attachment is wound for 100 to 115 volts, 25
to 125 cycles, and should, of course, be run from the same machine
which furnishes power to the circuit under observation. A rheostat
for steadying and adjusting the current should be connected in series
with the motor. =The beam from the vibrator mirrors= _striking this
synchronous mirror moves back and forth over the curved glass, and
gives the length of the wave; the movement of the vibrator mirror
gives the amplitude, and the combination gives the wave complete_. An
arc lamp or projection lantern produces the image reflected by the
mirrors upon the film, tracing table or screen. For the rotation of
the photographic film, a small direct current shunt wound motor is
ordinarily used.]

The ray then moves so as to produce an energy diagram on the
fluorescent screen.

[Illustration: FIG. 2,600.--General Electric moving coil
oscillograph. =The moving elements= _consist of single loops of flat
wire carrying a small mirror and held in tension by small spiral
springs_. The current passing down one side and up the other, forces
one side forward and the other backward, thus causing the mirror to
vibrate on a vertical axis. The vibrator elements fit into chambers
between the poles of electro-magnets, and are adjustable, so as to
move the beam from the mirror, both vertically and horizontally. A
sensitized photographic film is wrapped around a drum and held by
spring clamps. The drum, with film, is placed in a case and a cap
then placed over the end, making the case light, when the index is
either up or down. The loading is done in a dark room. A driving dog
is screwed into the drum shaft, and which, when the drum and case are
in place, revolves the film past a slot. =When an exposure is to be
made=, the index is moved from the closed position, thus opening the
slot in the case and exposing the film to the beam of light from the
vibrating mirrors when the electrically operated shutter is open. The
slot is then closed by moving the index to "=Exposed=." A slide with
ground glass can be inserted in place of the film case or roll holder
to arrange the optical system when making adjustments. The shutter
operating mechanism is arranged so as to hold the shutter open during
exactly one revolution of the film drum. There are two devices
connected to the shutter operating mechanism; one opens the shutter
at the instant the end of the film passes the slot; the other opens
immediately, at any part of the film, and both give exposure during
one revolution. The first is useful when making investigations in
which the events are either recurring, or their beginnings known or
under control, and the second when the time of the event is not under
control, such as the blowing of fuses or opening of circuit breakers.]

The instrument is much used in wireless telegraphy, as it is capable
of showing the characteristics of currents of very high frequency.

[Illustration: FIG. 2,601.--General Electric =moving coil
oscillograph= _with case removed_, =showing= _interior construction
and arrangement of parts_. The oscillograph is furnished complete
with a three element electro-magnet galvanometer, optical system,
shutter and shutter operating mechanism, film driving motor and cone
pulleys, photographic and tracing attachments, 6 film holders, and
the following repair parts, for vibrators: 6 extra suspension strips;
6 vibrator mirrors; 1 box gold leaf fuses; 1 bottle mirror cement; 1
bottle damping liquid.]

[Illustration: FIG. 2,602.--Oscillogram showing the direct current
pressure of a 25 cycle rotary converter (below), and (above) the
pressure wave taken between one collector ring and one commutator
brush. The 12 ripples per cycles in the direct current voltage are
due to a 13th harmonic in the alternating current supply.]

=Glow Light Oscillograph.=--This device consists of two aluminum rods
in a partially evacuated tube, their ends being about two millimeters
apart. When an alternating current of any frequency passes between
them a sheath of violet light forms on one of the electrodes, passing
over to the other when the current reverses during each cycle. The
phenomenon may be observed or photographed by means of a revolving
mirror.

[Illustration: FIG. 2,603.--Curves by Morris, _illustrating the_
=dangerous rush of current which may occur when switching on a
transformer=. The circuit was broken at F and made again at G. The
current was so great as to carry the spot of light right off the
photographic plate due to the fact that a residual field was left in
the core after switching off, and on closing the switch again the
direction of the current was such as to tend to build up the full
flux in the same direction as this residual flux. =The dotted lines=
have been drawn in _to show how the actual waves were distorted from
the normal_.]

=Moving Iron Oscillograph.=--This type is due to Blondel, to whom
belongs the credit of working out and describing in considerable
detail the principles underlying the construction of oscillographs.

     The moving iron type of oscillograph consists of a very thin
   vane of iron suspended in a powerful magnetic field, thus forming
   a polarized magnet. Near this strip are placed two small coils
   which carry the current whose wave form is to be measured.

     The moving iron vane has a very short period of vibration and
   can therefore follow every variation in the current.

[Illustration: FIG. 2,604.--Siemens-Blondel =moving coil type=
oscillograph. The coil is in the shape of a loop of thin wire, which
is suspended in the field of an electro-magnet excited by continuous
current. The current to be investigated is sent through this loop,
which in consequence of the interaction of current and magnetic
field, begins to vibrate. The oscillations are rendered visible by
directing a beam of light from a continuous current arc lamp onto a
small mirror fixed to the loop. The light reflected by the mirror is
in the form of a light strip, but by suitable means this is drawn
out in respect of time, so that a curve truly representing the
current is obtained. The loop of fine wire is stretched between two
supports and is kept in tension by a spring. As the spring tension
is considerable, the directive force of the vibrating system is
large, and its natural periodicity very high. The mirror is fixed in
the center of the loop, and has an area of 1 square mm. In order to
protect the loops from mechanical injury they are built into special
frames. The mirrors are of various sizes, the loop for demonstration
purposes (projection device) being provided with the largest
mirror and the most sensitive loop with a mirror of the smallest
dimensions.]

     Attached to the vane is a small mirror which reflects a beam of
   light upon some type of receiving device.

     The Siemens-Blondel oscillograph shown in fig. 2,604, is of
   the _moving coil_ type, being a development of the moving iron
   principle.

=Moving Coil Oscillograph.=--The operation of this form of
oscillograph is based _on the behaviour of a movable coil in a
magnetic field_.

[Illustration: FIGS. 2,605 and 2,606.--=Oscillograms= reproduced from
a paper by M. B. Field on "A Study of the =Phenomena of Resonance=
by the Aid of Oscillograms" (_Journal_ of _E. E._, Vol. XXXII). =The
effect of resonance= on the wave forms of alternators has been the
subject of much investigation and discussion; it is a matter of vital
importance to the engineer in charge of a large alternating current
power distribution system. Fig. 2,605 shows the pressure curve of an
alternator running on a length of unloaded cable, the 11th harmonic
being very prominent. Fig. 2,606 shows the striking alteration
produced by reducing the length of cable in the circuit and thus
causing resonance with the 13th harmonic.]

     It consists essentially of a modified moving coil galvanometer
   combined with a rotating or vibrating mirror, a moving
   photographic film, or a falling photographic plate. The
   galvanometer portion of the outfit is usually referred to as the
   oscillograph as illustrated in figs. 2,608 to 2,612, representing
   diagrammatically the moving system.

     In the narrow gap between the poles S, S of a powerful magnet
   are stretched two parallel conductors formed by bending a thin
   strip of phosphor bronze back on itself over an ivory pulley P.
   A spiral spring attached to this pulley serves to keep a uniform
   tension on the strips, and a guide piece L limits the length of
   the vibrating portion to the part actually in the magnetic field.

     A small mirror M bridges across the two strips as shown. The
   effect of passing a current through such a "vibrator" is to cause
   one of the strips to advance while the other recedes, and the
   mirror is thus turned about a vertical axis.

[Illustration: FIG. 2,607.--General view of electro-magnet
form of Duddell moving coil oscillograph, showing oil bath and
electro-magnet. This instrument is specially designed to have a very
high natural period of vibration (about 1/10,000 of a second) so as
to be suitable for accurate research work. It is quite accurate for
frequencies up to 300 per second. In the figure, A is the brass oil
bath in which two vibrators are fixed; B, core of electro-magnet
which is excited by two coils, one of which, C, is seen. The ends of
these two coils are brought out to four terminals at D, so that the
coils may be connected in series for 200 volt, or in parallel for 100
volt circuits. The bolts, E,E, hold the oil bath in position between
the poles of the magnet. F,F,F (one not seen), are levelling screws;
G,G, terminals of one vibrator; H, fuse; K, thermometer with bulb in
center of oil bath.]

[Illustration: FIGS. 2,608 to 2,612.--=Vibrator= of Duddell moving
coil oscillograph and =section through oil bath= of electro-magnet
oscillograph. =The vibrator consists of= a brass frame W, which
supports two soft iron pole pieces P,P. Between these, a long narrow
groove is divided into two parts by a thin soft iron partition,
which runs up the center. The current being led in by the brass wire
U, passes from an insulated brass plate to the strip, which is led
over an ivory guide block, down one of the narrow grooves and over
another guide block, the loops round the ivory pulley O, which puts
tension on the strip by the spring N, back to the guide block again,
up the other narrow groove, and out by way of the insulated brass
plate and lead U. Halfway up the grooves the center iron partition R
is partially cut away to permit of a small mirror M, bridging across
from one strip to the other, being stuck to the strips by a dot of
shellac at each corner. The figure illustrates one type of vibrator
in which P is removable from W for ease in repairing. In type 1,
these pole pieces P,P are not removable. =The vibrators= are placed
side by side in the gap between the poles S,S of the electro-magnet,
see fig. 2,610. Each vibrator is pivoted about vertical centers, the
bottom center fitting in the base of the oil bath, and the one at
the top being formed by a screw in the cock piece Y. It can thus be
easily turned in azimuth, its position being fixed by the adjusting
screw L, a spiral spring serving to keep the vibrator always in
contact with this screw. Since each cock piece can be independently
moved forward or backward, each vibrator can be tipped slightly in
either of these directions so that complete control over the mirrors
is obtained and reflected spots of light may be made to coincide with
that reflected from the fixed zero mirror, which latter is fixed to a
brass tongue in between the two vibrators. =A plano-convex lens= of
50 cm. focal length is fixed on the oil bath in front of the vibrator
mirrors to converge the reflected beams of light. It will be noticed
that this lens is slightly inclined so that no trouble will be given
by reflections from its own surface. The normal distance from the
vibrator mirrors to the scale of photographic plate is 50 cm., and
at this distance, a convenient working deflection on each side of
the zero line is 3 to 4 cm. This is obtained with a R.M.S. current
through the strips of from .05 to .1 of an ampere according to wave
form, etc. =The maximum deflection= on each side of the zero line
should not exceed 5 cm. while the maximum R.M.S. current through the
strips should in no case exceed .1 ampere.]

     Each strip of the loop passes through a separate gap (not shown
   in the figure). The whole of the "vibrator," as this part of the
   instrument is called, is immersed in an oil bath, the object
   of the oil being to damp the movement of the strips, and make
   the instrument dead beat. It also has the additional advantage
   of increasing by refraction the movement of the spot of light
   reflected from the vibrating mirrors.

     The beam of light reflected from the mirror M is received on
   a screen or photographic plate, the instantaneous value of the
   current being proportional to the linear displacement of the spot
   of light so formed.

     With alternating currents, the spot of light oscillates to and
   fro as the current varies and would thus trace a straight line.

     To obtain an image of the wave form, it is necessary to traverse
   the photographic plate or film in a direction at right angles to
   the direction of the movement of the spot of light.

[Illustration: FIG. 2,613.--Duddell =moving coil oscillograph= _with
projection and tracing desk outfit_. The outfit is designed for
teaching and lecture purposes. =In operation=, _after the beam of
light from the arc lamp has been reflected from the oscillograph
mirrors, it falls on a vibrating mirror which gives it a deflection
proportional to time in a direction at right angles to the deflection
it already has and which is proportional to the current passing
through the oscillograph_. It is therefore only necessary to place a
screen in the path of the reflected beam of light to obtain a trace
of the wave form. Since the vibrating mirror is vibrated by means
of a cam on the shaft of a synchronous motor, which motor is driven
from, or synchronously with, the source of supply whose wave form is
being investigated, the wave form is repeated time after time in the
same place on the screen, and owing to the "persistence" of vision,
the whole wave appears stationary on the screen. The synchronous
motor with its vibrating mirror, mentioned above, is located
underneath the "tracing desk." When used in this position a wave a
few centimeters in amplitude is seen through a sheet of tracing paper
which is bent round a curved sheet of glass. A permanent record of
the wave form can thus easily be traced on the paper. A _dark box_
which is designed to hold a sheet of sensitized paper in place of
the tracing paper, can be fitted in place of the tracing desk. Thus
an actual photographic record of the wave form is obtained. If the
synchronous motor be transferred from its position underneath the
tracing desk to the space reserved for it close to the oscillograph,
the beam of light is then received on a large mirror which is placed
at an angle of about 45 degrees to the horizontal and so projects the
wave form onto a large vertical screen which should be fixed about
two and a half meters distant. Under these conditions a wave form of
amplitude 50 cm. each side the zero line may be obtained which is
therefore visible to a large audience.]

=Ques. How are the oscillograms obtained in the Duddell moving coil
oscillograph?=

Ans. In all cases the oscillograms are obtained by a spot of light
tracing out the curve connecting current or voltage with time. The
source of light is an arc lamp, the light from which passes first
through a lens, and then, excepting when projecting on a screen,
through a rectangular slit about 10 mm. long by 1 mm. wide. The
position of the lamp from the lens is adjusted till an image of the
arc is obtained covering the three (two moving, one fixed) small
oscillograph mirrors. The light is reflected back from these mirrors
and, being condensed by a lens which is immediately in front of them,
it converges till an image of the slit is formed on the surface where
the record is desired. All that is necessary now to obtain a bright
spot of light instead of this line image is to introduce in the path
of the beam of light a cylindrical lens of short focal length.

[Illustration: FIGS. 2,614 and 2,615.--Sectional view of =permanent
magnet form= of Duddell =moving coil oscillograph.= This instrument
has a lower natural period of vibration (1/3000 second) than the
type shown in fig. 2,612, and therefore is not capable of accurately
following wave forms of such high frequency, but it is sufficiently
quick acting to follow wave forms of all ordinary frequencies with
perfect accuracy. It is easier to repair, and more portable owing to
the fact that the magnetic field is produced by a permanent magnet
instead of an electro-magnet. This also renders the instrument
suitable for use on high tension circuits without earth connection,
as, owing to the fact that no direct current excitation is required,
the instrument is more easily insulated than other types.]

=Ques. What is the function of the mirrors on the vibrating vane?=

[Illustration: FIG. 2,616.--Diagram of connections of Duddell
oscillograph =to high pressure circuit.= The modification necessary
for high pressure circuit only applies to the vibrator which gives
the pressure wave and consists in adding two more resistances, R_{4}
and R_{5}. Referring to fig. 2,617, it will be seen that in case fuse
f_{2} blows, or the vibrator be accidentally broken, the full supply
voltage is immediately thrown on the instrument itself. This is not
permissible in high voltage work and therefore the resistance R_{5}
is introduced as a permanent shunt to the oscillograph vibrator.
The resistance R_{4} is an exact duplicate of R_{2} being a 21 ohm
plug resistance box for adjusting the sensitivity of the vibrator
to an even figure. =In practice= R_{5} is usually a part of R_{1},
and in most of the high voltage resistances, two taps are brought
out near one end to serve as R_{5}. One of these taps is usually 50
ohms distant from the end terminal and the other only 5 ohms from
the end. =The use of these taps is as follows:= The large resistance
consisting of R_{1} + R_{5} is so chosen with respect to the voltage
of the circuit under investigation that the current through R_{1} is
about .1 ampere. _It should never be more than this continuously._
Then R_{4} is connected to the 50 ohm tap, and since the resistance
of the oscillograph vibrator circuit is variable from about 5 to
26 ohms by means of R_{4}, the current can be controlled through
the oscillograph from about .066 to .091 of an ampere, enabling an
open wave form to a convenient scale to be obtained. =If it now
be desired to record large rises of pressure,= such as may occur
in cases of resonance, _the height of the wave must be reduced in
order to keep these rises on the plate_. This is accomplished by
disconnecting R_{4} from the 50 ohm tap and connecting it to the 5
ohm tap, when the current through the vibrator will be from .05 to
.016 of an ampere according to whether the resistance R_{4} is in
or out of circuit. When, instead of using the _falling plate_, the
_cinematograph_ camera is being used, it becomes necessary always
to work on the 5 ohm tap since the width of the film is much less
than that of the plate, and the current must therefore be less.
=In experiments where sudden rises of voltage are expected= _it is
often advisable to keep_ R_{1} _as great as possible._ That end of
the resistance R_{1} referred to as R_{5} in the diagram should be
securely connected to the supply main and no switch or fuse used. A
switch may, if desired, be used in series with R_{1}, provided it be
inserted at the point where R_{1} joins the supply main remote from
R_{5}. It will be seen that fuses f_{1} and f_{2} are shown. Provided
that the connections are always made in accordance with the diagram,
and the vibrators are always shunted by R_{5} or R_{3} respectively,
there is not much objection to the use of these fuses, but on general
principles it is wise to avoid fuses in high tension work and
accordingly with each permanent magnet oscillograph, dummy fuses are
supplied, which can be inserted in place of the ordinary fuses when
desired. _The remark previously made about keeping both vibrators
and the frame of the instrument at approximately the same pressure
applies with additional emphasis in high pressure work._]

Ans. They simply control the direction of a beam of light in a
horizontal plane in such a manner that its deflection from a zero
position depends on the current passing through the instrument, and
it is therefore evident that the oscillograph is not complete without
means of producing a time scale.

[Illustration: FIG. 2,617.--Diagram of connections of Duddell
oscillograph =to low pressure circuit=, R_{1} is a high non-inductive
resistance connected across the mains in series with one of
the vibrators. S_{2} is a switch, and f_{2}, the fuse (on the
oscillograph in this circuit). The resistance of R_{1} in ohms
should be rather more than ten times the voltage of the circuit,
so that a current of a little less than .1 of an ampere will pass
through it. The vibrator will then give the curve of the circuit
on an open scale. (For the projection oscillograph, the resistance
R_{1} should be only twice the supply voltage, since .5 of an ampere
is required to give full scale deflection on a large screen.) =To
obtain the current wave form=, _the shunt_ R_{3} _is connected in
series with the circuit under investigation and the second vibrator
is connected across this shunt_. Here also f_{1} is a fuse, S_{1} a
switch, and R_{2} an adjustable resistance box. The switch S_{1} is
however unnecessary if the plug resistance box supplied for R_{2}
be used, since an infinity plug is included in this box. The shunt
R_{3} should have a drop of about 1 volt across it in order to give
a suitable working current through the vibrator. The resistance
R_{2} is not absolutely essential, but it is a great convenience in
adjusting the current through the vibrator. It is a plug resistance
box, the smallest coil being .04 of an ohm and the total 21 ohms.
Being designed to carry .5 ampere continuously it can be used
with any other type of Duddell oscillograph, and by its use the
sensitiveness of the vibrator can be adjusted so that a round number
of amperes in the shunt gives 1 mm. deflection. This adjustment is
best made with direct current. =It should be noted= in connecting
the oscillograph in circuit, that _the two vibrators should be so
connected to the circuit that it is impossible that a higher pressure
difference than_ 50 _volts should exist between one vibrator and the
other, or between either vibrator and the frame_. To ensure attention
to this important point, a brass strap is provided which connects
the two vibrators together and to the frame of the instrument. This
does not mean that this point must necessarily be earthed since the
frame of the instrument is insulated from the earth. It is advisable,
however, to earth it when possible.]

[Illustration: FIGS. 2,618 and 2,619.--=Two curves= _obtained with
the_ =falling plate camera= and illustrating _the discharge of a
condenser through an inductive circuit_. =When taking curve A= the
resistance in the circuit was very small compared to the inductance,
while =before taking curve B= an additional non-inductive resistance
was inserted in the circuit so that the oscillations were damped out
much more rapidly although the periodic time remained approximately
constant.]

=Ques. How is the time scale produced?=

Ans. Either the surface on which the beam of light falls may be
caused to move in a vertical plane with a certain velocity, so that
the intersection of the beam and the plane surface traces out a curve
connecting current with time (a curve which becomes a permanent
record if a sensitized surface be used); or, the surface may remain
stationary and in the path of the horizontally vibrating beam may be
introduced a mirror which rotates or vibrates about a horizontal
axis, thus superposing a vertical motion proportional to time on the
horizontal vibration which is proportional to current, and causing
the beam of light to trace out a curve connecting current and time on
the stationary surface.

=Ques. What kind of recording apparatus is used with the Duddell
oscillograph?=

Ans. A falling plate camera, or a cinematograph film camera.

[Illustration: FIG. 2,620.--Synchronous motor with vibrating mirror
as used with Duddell moving coil oscillograph. =Since the motor must
run synchronously= with the wave form it is required to investigate,
_it should be supplied with current from the same source_. The motor
can be used over a wide range of frequencies (from 20 to 120). When
working at frequencies below 40, it is advisable to increase the
moment of inertia of the armature, and for this purpose a suitable
brass disc is used. =The armature carries a sector=, _which cuts off
the light from the arc lamp during a fraction of each revolution, and
a cam which rocks the vibrating mirror_. =It makes one revolution
during two complete periods=, and the cam and sector are so arranged
that during 1½ periods, the mirror is turning with uniform angular
velocity, while during the remaining half period, the mirror is
brought back quickly to its angular position, the light being cut off
by the sector during this half period.]

=Ques. Explain the operation of the falling plate camera.=

Ans. In this arrangement a photographic plate is allowed to fall
freely by the force of gravity down a dark slide. At a certain point
in its fall it passes a horizontal slit through which the beams of
light from the oscillograph pass, tracing out the curves on the plate
as it falls.

[Illustration: FIGS. 2,621 to 2,623.--Interior of cinematograph
camera as used on Duddell moving coil oscillograph =for obtaining
long records=. The loose side of case is shown removed and one of
the reels which carry the film lying in front. =The spool of film=
which is placed on the loose reel A, passes over the guide pulley
B, then vertically downward between the brass gate D (shown open in
the figure), and the brass plate C. =The exposure aperture= is in
the plate C and can be opened or closed by a shutter controlled by
the lever M. The groove in the plate C, and the springs which press
the gate D flat on the plate C, prevent the film having any but a
vertical motion as it passes the exposure slit. E is the sprocket
driving pulley which engages with the perforations on the film and
unwinds it from the reel A to reel H. Outside the case on the far
side of it is secured to the axle G a three speed cone pulley. This
is driven by a motor of about 1/7 horse power, which also drives,
through the gears shown, the sprocket pulley E. Close to the grooved
cone pulley is a lever carrying a jockey pulley L, and a brake, which
latter is normally held onto the cone pulley by a spring and so
causes the loose belt to slip. By pressing a lever which is attached
to the falling plate camera case, the brake can be suddenly released
and at the same time the jockey pulley caused to tighten the belt
onto the grooved cone pulley, so that the starting and stopping of
the film is controlled independently of the driving motor, and being
quickly accomplished avoids waste of film. =Both reels= are alike and
each is made in two pieces. =The upper reel= is loose on its axle and
its motion is retarded slightly by a friction brake. =The lower reel=
is also loose on its axle, but it is driven by means of a friction
clutch, the clutch always rotating faster than the reel so that the
used film delivered by the sprocket pulley E is wound up as fast as
delivered. K is the front face of one reel, the boss on it pushes
into the tube on the other half H, which serves not only to unite the
two halves, but also to secure the end of the film which is doubled
through J.]

     The mean speed of the plate at the moment of exposure is about
   13 feet per second. This speed is very suitable for use with
   frequencies of from 40 to 60 periods per second. A cloth bag is
   used to introduce the plate to the slide.

     A catch holds the plate until it is desired to let it fall.
   Inside the case, is a small motor, 100 or 200 volts direct
   current, driving four mirrors which are fixed about a common axis
   with their planes parallel to it.

[Illustration: FIG. 2,624.--Portion of oscillograph record taken with
cinematograph film camera, =showing the rush of current= and =sudden
rise of voltage= _at the moment of switching on a high pressure
feeder_.]

     By looking through a small slot in the end of the camera into
   these rotating mirrors, the observer sees the wave form which the
   oscillograph is tracing out and is thus able to make sure that
   he is obtaining the particular wave form or other curve desired
   before exposing the plate.

[Illustration: FIG. 2,625.--Portion of oscillograph record taken with
a cinematograph film camera =showing the effect of switching off
a high pressure feeder= and illustrating the violent fluctuations
produced by sparking at the switch contacts.]

     The plate falls into a second red cloth bag which is placed on
   the bottom of the slide. The plates used are "stereoscopic size",
   6¾" × 3¼" (17.1 × 8.3 cm.).

=Ques. For what use is the cinematograph camera adapted?=

Ans. For long records.

     For instance, in investigations, such as observation on the
   paralleling of alternators, the running up to speed of motors,
   and the surges which may occur in switching on and off cable,
   etc. The cinematograph camera fits on to the falling plate case
   and by means of which a roll of cinematograph film can be driven
   at a uniform speed past the exposure aperture, enabling records
   up to 50 metres in length to be obtained. An interior view of the
   cinematograph camera is shown in fig. 2,621.

[Illustration: FIG. 2,626.--Curves reproduced from an article by J.
T. Morris in the _Electrician_. "On recording transitory phenomena by
the oscillograph."]

[Illustration: FIG. 2,627.--First rush of current from an alternator
when short circuited, showing unsymmetrical initial wave of current,
becoming symmetrical after a few cycles. 25 cycles.]

[Illustration: FIG. 2,628.--Pressure wave obtained from narrow
exploring coil on alternator armature, indicating distribution of
field flux. The terminal voltage of the alternator is very nearly a
sine wave, 60 cycles; about 17 volts.]

SOME OSCILLOGRAPH RECORDS

[Illustration: FIG. 2,629.--The waves of voltage and current of an
alternating arc. A, voltage wave; B, current wave showing low power
factor of the arc without apparent phase displacement. 60 cycles.]

[Illustration: FIG. 2,630.--Rupturing 650 volt circuit. A, current
wave; B, 25 cycle wave to mark time scale.]

[Illustration: FIG. 2,631.--First rush of current from alternator
when short circuited, showing unsymmetrical current wave, also wave
of field current caused by short circuit current in armature. Upper
curve, armature current; lower curve, field current.]

[Illustration: FIG. 2,632.--Mazda (tungsten) lamp, showing rapid
decrease to normal current as filament heats up. 25 cycles.]

[Illustration: FIG. 2,633.--Current wave in telephone line
corresponding to sustained vowel sound "_i_," as in machine; voice
pitched at A 110.]

[Illustration: FIG. 2,634.--Carbon lamp, showing rapid increase to
normal current as filament heats up. 25 cycles.]

[Illustration: FIG. 2,635.--Short circuit current on direct current
end of rotary converter, 21,500 amperes maximum. Upper curve, direct
current voltage; lower curve, direct current amperage. Duration of
short circuit about .1 second.]



CHAPTER LXIV

SWITCHBOARDS


=General Principles of Switchboard Connections.=--The interconnection
of generators, transformers, lines, bus bars, and switches with
their relays, in modern switchboard practice is shown by the
diagrams, figs. 2,636 to 2,645. The figures being lettered A to J
for simplicity, the generators are indicated by black discs, and the
switches by open circles, while each heavy line represents a set of
bus bars consisting of two or more bus bars according to the system
of distribution. It will be understood, also, in this connection,
that the number of pole of the switches and the type of switch will
depend upon the particular system of distribution employed.

     Diagram A, shows the simplest system, or one in which a single
   generator feeds directly into the line. There are no transformers
   or bus bars and only one switch is sufficient.

     In B, a single generator supplies two or more feeders through a
   single set of bus bars, requiring a switch for each feeder, and a
   single generator switch.

     In C, two generators are employed and required and the addition
   of a bus section switch.

     D, represents a number of generators supplying two independent
   circuits. The additional set of bus bars employed for this purpose
   necessitates an additional bus section switch, and also additional
   selector switches for both feeders and generators.

     E, shows a standard system of connection for a city street
   railway system having a large number of feeders.

[Illustration: FIGS. 2,645 and 2,646.--Diagrams illustrating general
principles of switchboard connections.]

     This arrangement allows any group of feeders to be supplied from
   any group of generators.

[Illustration: FIG. 2,646.--Fort Wayne switchboard panel for one
alternator and one transfer circuit. Diagram giving dimensions,
arrangement of instruments of board, and method of wiring. The
different forms of standard alternating current switchboard panels
for single phase circuits made by the Fort Wayne Electric Works are
designed to fulfill all the usual requirements of switchboards for
this class of work. The line includes panels equipped for a single
generator; for one generator and two circuits; one generator and one
transfer circuit; one generator, an incandescent and an arc lighting
circuit; and also feeder panels of different kinds.]

     It also permits the addition of a generator switch for each
   generator.

     F, represents the simplest system with transformers.

     It requires a single generator transformer bank, switch and
   line. The arrangement as show at F is used where a number of
   plants supply the same system.

     G, represents a system having more than one line.

     In this case a bus bar and transformer switch is used on the
   high tension side.

     H, shows a number of generators connected to a set of low
   tension bus bars through generator switches, and employing a low
   tension transformer switch.

     I, shows the connections of a system having a large number of
   feeders supplied by several small generators. In this case, the
   plant is divided into two parts, each of which may be operated
   independently.

[Illustration: FIG. 2,647.--General Electric =small plant alternating
current switchboard=, _designed for use in small central stations and
isolated plants_. They are for use with one set of bus bars, to which
all generators and feeders are connected by means of single throw
lever switches or circuit breakers, suitable provision being made for
the parallel operation of the generators.]

     J, represents the arrangement usually employed in modern plants
   where the generator capacity is large enough to permit of a
   generator transformer unit combination with two outgoing lines. By
   operating in parallel on the high tension side only, any generator
   can be run with any transformer. The whole plant can be run in
   parallel, or the two parts can be run separately.

[Illustration: FIG. 2,648.--Crouse-Hinds =voltmeter and ground
detector radial switch=, arranged for mounting on the switchboard.
The switch proper is placed on the rear of the board with hand wheel,
dial, and indicator only on the front side. The current carrying
parts are of hard brass, with contact surfaces machined after
assembling. The contact parts are of the plunger spring type, and the
cross bar has fuse connections. Ground detector circuits are marked
G+ and G- for two wire system, and G+, G-, GN+ and GN- for three wire
system. When the voltmeter switch is to be used as a ground detector,
two circuits are required for a two wire system, and four circuits
for a three wire system, that is, a six circuit voltmeter and ground
detector switch for use on a two wire system has two circuits for
ground detector and four circuits for voltmeter readings. A six
circuit voltmeter and ground detector switch, for use on a three wire
system, has four circuits for ground detector and two circuits for
voltmeter readings.]

=Switchboard Panels.=--The term "panel" means the slab of marble or
slate upon which is mounted the switches, and the indicating and
controlling devices. There are usually several panels comprising
switchboards of moderate or large size, these panels being classified
according to the division of the system that they control, as for
instance:

  1. Generator panel;
  2. Feeder panel;
  3. Regulator panel, etc.

     In construction, the marble or slate should be free from
   metallic veins, and for pressures above, say, 600 volts, live
   connections, terminals, etc., should preferably be insulated from
   the panels by ebonite, mica, or removed from them altogether, as
   is generally the case with the alternating gear where the switches
   are of the oil type.

[Illustration: FIGS. 2,649 and 2,650,--Wiring diagrams of
Crouse-Hinds voltmeter and ground detector switches. Fig. 2,649
voltmeter switch; fig. 2,650 voltmeter and ground detector switch. A
view of the switch is shown in fig. 2,648; it is designed for use on
two or three wire systems up to 300 volts.]

     The bus bars and connections should be supported by the
   framework at the back of the board, or in separate cells, and the
   instruments should be operated at low pressure through instrument
   transformers.

     The panels are generally held in position by bolting them to an
   angle iron, or a strip iron framework behind them.

=Generator Panel.=--This section of a switchboard carries the
instruments and apparatus for measuring and electrically controlling
the generators. On a well designed switchboard each generator has, as
a rule, its own panel.

[Illustration: FIGS. 2,651 to 2,653.--Diagrams of connections for
generator panels. =Key to symbols=: =A=, ammeter; =A.S.=, ammeter
switch; =C.T.=, current transformer; =F.=, fuse; =F.A.=, direct
current field ammeter; =F.S.=, field switch; =G.C.S.=, governor
control switch; =L.S.=, limit switch (included with governor motor);
=O.S.=, oil switch; =P.I.W.=, polyphase indicating wattmeter;
=P.W.M.=, polyphase watthour meter; =P.R.=, pressure receptacle;
=P.P.=, pressure plug; =Rheo.=, rheostat; =S.=, shunt; =S.R.=,
synchronizing receptacle; =S.P.=, synchronizing plugs; =T.B.=,
terminal board for instrument leads; =V=, alternating current
voltmeter.]

[Illustration: FIGS. 2,654 and 2,655.--Diagrams illustrating =a
simple method of determining bus capacity= as suggested by the
General Electric Co. Fig. 2,654 relates to any panel; the method is
as follows: =1.= Make a rough plan of the _entire board_, regardless
of the number of panels to be ordered. _The order of panels_
shown is recommended, it being most economical of copper and best
adapted to future extensions. =2.= To avoid confusion keep on one
side of board everything pertaining to exciter buses, and on other
side everything pertaining to A. C. buses. =3.= With single lines
represent the exciter and A. C. buses across such panels as they
actually extend and by means of arrows indicate that portion of each
bus which is connected to feeders and that portion which is connected
to generators. _Remember that "Generator" and "Feeder" arrows must
always point toward each other_, otherwise the rules given below do
not hold. Note also that the field circuits of alternator panels are
treated as D. C. feeders for the exciter bus. =4.= On each panel
mark its ampere rating, that is, the maximum current it supplies
to or takes from the bus. For A. C. alternator panels the D. C.
rating is the excitation of the machines. =5.= Apply the following
rules _consecutively_, and note their application in fig. 2,654.
(For the sake of clearness ampere ratings are shown in light face
type and bus capacities in large type.) =A.= _Always begin with the
tail of the arrow and treat "generator" and "feeder" sections of
the bus separately._ =B.= _Bus capacity for first panel = ampere
rating of panel._ =C.= _Bus capacity for each succeeding panel =
ampere rating of panel plus bus capacity for preceding panel._ (See
sums marked above the buses in fig. 2,654.) =D.= _For a panel not
connected to a bus extending across it, use the smaller value of
the bus capacities already obtained for the two adjoining panels._
(See exciter bus for panel C.) =E.= _The bus capacity for any feeder
panel need not exceed the maximum for the generator panels_ (see A.
C. bus for panel G) _and vice versa_ (see exciter bus for panel B).
Hence the corrections made in values obtained by applying rules =B=
and =C=. The arrangement of panels shown in fig. 2,654 is the one
which is mostly used. The above method may, however, be applied to
other arrangements, one of which is shown in fig. 2,655. Here the
generators must feed both ways to the feeders at either end of the
board so that in determining A. C. bus capacities it is necessary to
first consider the generators with the feeders at one end, and then
with the feeders at the other end as shown by the dotted A. C. buses.
The required bus capacities are then obtained by taking the maximum
values for the two cases.]

[Illustration: FIG. 2,656.--End view showing =general arrangement of
switchboards= for 240, 480, and 600 volt alternating current. The cut
shows a single throw oil switch mounted on the panel.]

In the case of a dynamo, a good representative panel would have
mounted upon it a reverse current circuit breaker, an ammeter, a
double pole main switch (or perhaps a single pole switch, since
the circuit breaker could also be used as a switch) a double pole
socket into which a plug could be inserted to make connection with
a voltmeter mounted on a swinging bracket at the end of the board;
a rheostat handle, the spindle of which operates the shunt rheostat
of the machine, the rheostat being placed either directly behind
the spindle, if of small size, or lower down with chain drive from
the hand wheel spindle, if of larger size, a field discharge switch
and resistance, a lamp near the top of the panel for illuminating
purposes, a fuse for the voltmeter socket, and, if desired, a
watthour meter. If the dynamo be compound wound, the equalizing
switch will generally be mounted on the frame of the machine, and in
some cases the field rheostat will be operated from a pillar mounted
in front of the switchboard gallery. If the generator be for traction
purposes, the circuit breaker is more often of the maximum current
type, and a lightning arrester is often added, without a choke coil,
the latter as well as further lightning arresters being mounted on
the feeder panels.

[Illustration: FIGS. 2,657 and 2,658.--Two views of a =feeder panel=,
showing general arrangement of the devices assembled thereon. A,
circuit breaker; B, ammeter; C, voltmeter; D, switches.]

In the case of a high pressure alternating current plant of
considerable size, the bus bars oil switches, and the current and
pressure transformers are generally mounted either in stoneware
cells, or built on a framework in a space guarded by expanded metal
walls, and no high pressure apparatus of any sort is brought on to
the panels themselves.

[Illustration: FIGS. 2,659 to 2,666.--Diagram of connections for
three phase feeder panels. =Key to symbols=: A, ammeter; A.S.,
three way ammeter switch; B.A.S., bell alarm switch; C.T., current
transformer; F, fuse; O.S., oil switch; P.I.W., polyphase indicating
wattmeter; P.W.M., polyphase watthour meter; T.B., terminal board;
T.C., trip coils for oil switch.]

=Feeder Panel.=--The indicating and control apparatus for a feeder
circuit is assembled on a panel called the feeder panel.

The most common equipment in the case of a direct current feeder
panel comprises an ammeter, a double pole switch, and double pole
fuses or instead of the fuses, a circuit breaker on one or both
poles; in the case of a traction feeder a choke coil and a lightning
arrester are often added.

[Illustration: FIGS. 2,667 and 2,668.--Diagrams of connections for
two phase and three phase installations: A and A1, ammeter; C.C.,
constant current transformer; C.T., current transformer; D.R.,
discharge resistance; F, fuse; F.S., field switch; L.A., lightning
arrester; O.S., oil switch; P.P., pressure plug; P.R., pressure
receptacle; P.T., pressure transformer; S and S1, plug switches;
T.C., oil switch trip coil; V, voltmeter.]

The equipment of a typical high pressure three phase feeder panel is
an ammeter (sometimes three ammeters, one in each phase) operated
by a current transformer, and oil break switch with two overload
release coils, or three if the neutral of the circuit be earthed, the
releases being operated by current transformers.

[Illustration: FIG. 2,669.--Crouse-Hinds radial ammeter switch,
arranged for mounting directly on the switchboard. It is designed
for use with external shunt ammeters of any make or capacity, and in
connection with the required number of shunts, makes possible the
taking of current readings of a corresponding number of circuits by
means of one ammeter. The wiring diagram is shown in fig. 2,670.]

The switch when on a large system is often in a cell some distance
behind the panel, and is then controlled by a system of levers, or by
a small motor which is started and stopped by a throw over switch on
the panel, in which case there is generally a lamp or lamps on the
panel to show whether the switch is open or closed.

     Air brake switches or links are placed between the bus bars
   and the oil switch to allow of the latter being isolated for
   inspection purposes, and as a general rule no apparatus carrying
   high pressure current is allowed on the front of the panel. With
   both direct and alternating current feeders, a watthour meter is
   often added to show the total consumption of the circuit.

[Illustration: FIG. 2,670.--Wiring diagram for Crouse-Hinds radial
ammeter switch as illustrated in fig. 2,669. The switch proper is on
the rear of the switchboard, and the hand wheel dial and indicator on
the front.]

     A typical three phase generator panel is provided with three
   ammeters, one in each phase, operated from three current
   transformers, one to each ammeter, a volt meter, a power factor
   indicator, and an indicating watthour meter, all operated from
   one or more pressure transformers, and the necessary current
   transformers, the operating handle of the oil switch, which is
   connected to the switch itself by means of rods, two maximum
   releases operated by current transformers, or a reverse relay
   for automatically tripping the switch, lamps for indicating when
   the switch is tripped, a socket for taking the plug which makes
   connection between the secondary of a pressure transformer and
   the synchronizer on the synchronizing panel, and a lamp for
   illuminating purposes, while on the base of the panel or on a
   pillar at the front of the gallery is mounted the gear for the
   field circuit. This consists of a double pole field switch and a
   discharge resistance, an ammeter, a handle for the rheostat in
   the generator field, and (if each alternator have its own direct
   coupled exciter) possibly also a small rheostat for the exciter
   field.

            NOTE.--In some cases where the capacity of
          the plant is not very great, the oil switch
          is mounted on the back of the panel, and the
          bus bars, current transformers, &c., on the
          framework, also just at the back of the panel,
          but under no circumstances, in good modern
          practice, is high pressure apparatus permitted
          on the front of the board. Where the capacity of
          the plant is very large, the oil switches are
          operated electrically by means of small motors,
          and in this case the small switch gear for
          starting and stopping this motor is mounted on
          the generator panel, also the lamp or lamps to
          indicate when the switch is open, and when closed.



CHAPTER LXV

=ALTERNATING CURRENT WIRING=


In the case of alternating current, because of its peculiar
behaviour, there are several effects which must be considered in
making wiring calculations, which do not enter into the problem with
direct current.

Accordingly, in determining the size of wires, allowance must be made
for

  1. Self-induction;
  2. Mutual-induction;
  3. Power factor;
  4. Skin effect;
  5. Corona effect;
  6. Frequency;
  7. Resistance.

     Most of these items have already been explained at such length,
   that only a brief summary of facts need be added, to point out
   their connection and importance with alternating current wiring.

=Induction.=--The effect of induction, whether self-induction
or mutual induction, is to set up a back pressure of _spurious
resistance_, which must be considered, as it sometimes materially
affects the calculation of circuits even in interior wiring.

     _Self-induction is the effect produced by the action of the
   electric current upon itself during variations in strength._

=Ques. What conditions besides variations of current strength governs
the amount of self-induction in a circuit?=

Ans. The shape of the circuit, and the character of the surrounding
medium.

     If the circuit be straight, there will be little self-induction,
   but if coiled, the effect will become pronounced. If the
   surrounding medium be air, the self-induction is small, but if it
   be iron, the self-induction is considerable.

[Illustration: FIGS. 2,671 to 2,676.--=The effect of self-induction.=
In a non-inductive circuit, as in fig. 2,672, the whole of the
virtual pressure is available to cause current to flow through the
lamp filament, hence it will glow with maximum brilliancy. If an
inductive coil be inserted in the circuit as in fig. 2,674, the
reverse pressure due to self-induction will oppose the virtual
pressure, hence the effective pressure (which is the difference
between the virtual and reverse pressures), will be reduced and
the current flow through the lamp diminished, thus reducing the
brilliancy of the illumination. The effect may be intensified to such
degree by interposing an iron core in the coil as in fig. 2,676, as
to extinguish the lamp.]

=Ques. With respect to self-induction, what method should be followed
in wiring?=

Ans. When iron conduits are used, the wires of each circuit should
not be installed in separate conduits, because such arrangement will
cause excessive self-induction.

     The importance of this may be seen from the experience of one
   contractor, who installed feeders and mains in separate iron
   pipes. When the current was turned on, it was found that the
   self-induction was so great as to reduce the pressure to such an
   extent that the lamps, instead of giving full candle power, were
   barely red. This necessitated the removal of the feeders and main
   and re-installing them, so that those of the same circuit were in
   the same pipe.

=Ques. What is mutual induction?=

Ans. Mutual induction is the effect of one alternating current
circuit upon another.

[Illustration: FIG. 2,677.--Measurement of self induction when
the frequency is known. The apparatus required consists of a high
resistance or electrostatic a.c. voltmeter, d.c. ammeter, and a
non-inductive resistance. Connect the inductive resistance to be
measured as shown, and close switch M, short circuiting the ammeter.
Connect alternator in circuit and measure drop across R and across
X_{_i_}. Disconnect alternator and connect battery in circuit, then
open switch M and vary the continuous current until the drop across R
is the same as with the alternating current, both measurements being
made with the same voltmeter; read ammeter, and measure drop across
X_{_i_}. Call the drop across X_{_i_} with alternating current E, and
with direct current E_{_i_}, and the reading of the ammeter J. Then
     ____________________
L = √E^{2} + E_{_i_}^{2} ÷ 2π _f_ I. If the resistance X_{_i_}
be known, and the ammeter be suitable for use with alternating
current, the switch and R may be dispensed with.

          ______________________________
Then L = √E^{2} - X_{_i_}^{2} I_{_i_}^{2} ÷ 2π _f_ I,
where I_{_i_} is the value of the alternating current. The resistance
of the voltmeter should be high enough to render its current
negligible as compared with that through X_{_i_}.]

=Ques. How is it caused?=

Ans. It is due to the magnetic field surrounding a conductor cutting
adjacent conductors and inducing back pressures therein.

     This effect as a rule in ordinary installations is negligible.

=Transpositions.=--The effect of mutual induction between two
circuits is proportional to the inter-linkage of the magnetic fluxes
of the two lines. This in turn depends upon the proximity of the
lines and upon the general relative arrangement of the conductors.

[Illustration: FIG. 2,678.--Transposition diagram for two parallel
lines consisting of two wires each.]

[Illustration: FIG. 2,679.--Transposition diagram for three phase,
three wire line, transposing at the vertices of an equilateral
triangle. The line is originally balanced and becomes unbalanced on
transposing, a procedure which should be resorted to only to prevent
_mutual induction_.]

[Illustration: FIG. 2,680.--Transposition diagram of three phase,
three wire line, with center arranged in a straight line.]

The inductive effect of one line upon another is equal to the
algebraic sum of the fluxes due to the different conductors of the
first line, considered separately, which link the secondary line.

The effect of mutual induction is to induce surges in the line where
a difference of frequency exists between the two currents, and to
induce high electrostatic charges in lines carrying little or no
current, such as telephone lines.

  INDUCTANCE PER MILE OF THREE PHASE CIRCUIT

  ---------+-------+----------+------------
           | Diam. | Distance |    Self
    Size   |  in   |  _d_ in  | Inductance
   B. & S. | inch. |  inches. |  L henrys.
  ---------+-------+----------+------------
    0000   |  .46  |    12    |   .00234
           |       |    18    |   .00256
           |       |    24    |   .00270
           |       |    48    |   .00312
           |       |          |
     000   |  .41  |    12    |   .00241
           |       |    18    |   .00262
           |       |    24    |   .00277
           |       |    48    |   .00318
           |       |          |
      00   |  .365 |    12    |   .00248
           |       |    18    |   .00269
           |       |    24    |   .00285
           |       |    48    |   .00330
           |       |          |
       0   |  .325 |    12    |   .00254
           |       |    18    |   .00276
           |       |    24    |   .00293
           |       |    48    |   .00331
           |       |          |
       1   |  .289 |    12    |   .00260
           |       |    18    |   .00281
           |       |    24    |   .00308
           |       |    48    |   .00338
           |       |          |
       2   |  .258 |    12    |   .00267
           |       |    18    |   .00288
           |       |    24    |   .00304
           |       |    48    |   .00314
           |       |          |
       3   |  .229 |    12    |   .00274
           |       |    18    |   .00294
           |       |    24    |   .00310
           |       |    48    |   .00351
           |       |          |
       4   |  .204 |    12    |   .00280
           |       |    18    |   .00300
           |       |    24    |   .00315
           |       |    48    |   .00358
           |       |          |
       5   |  .182 |    12    |   .00286
           |       |    18    |   .00307
           |       |    24    |   .00323
           |       |    48    |   .00356
           |       |          |
       6   |  .162 |    12    |   .00291
           |       |    18    |   .00313
           |       |    24    |   .00329
           |       |    48    |   .00369
           |       |          |
       7   |  .144 |    12    |   .00298
           |       |    18    |   .00310
           |       |    24    |   .00336
           |       |    48    |   .00377
           |       |          |
       8   |  .128 |    12    |   .00303
           |       |    18    |   .00325
           |       |    24    |   .00341
           |       |    48    |   .00384
           |       |          |
       9   |  .114 |    12    |   .00310
           |       |    18    |   .00332
           |       |    24    |   .00348
           |       |    48    |   .00389
           |       |          |
      10   |  .102 |    12    |   .00318
           |       |    18    |   .00340
           |       |    24    |   .00355
           |       |    48    |   .00396
  ---------+-------+----------+------------

This effect may be nullified by separating the lines and by
transposing the wires of one of the lines so that the effect produced
in one section is opposed by that in another. Of two parallel lines
consisting of two wires each, one may be transposed to neutralize the
mutual inductance.

     Fig. 2,678 shows this method. The length L' should be an even
   factor of L so that to every section of the line transposed there
   corresponds an opposing section.

[Illustration: FIG. 2,681.--Capacity effect in single phase
transmission line. The effect is the same as would be produced by
shunting across the line at each point an infinitesimal condenser
having a capacity equal to that of an infinitesimal length of
circuit. For the purpose of calculating the charging current, a very
simple and sufficiently accurate method is to determine the current
taken by a condenser having a capacity equal to that of the entire
line when charged to the pressure on the line at the generating end.
The effect of capacity of the line is to reduce the pressure drop,
that is, improve the regulation, and to decrease or increase the
power loss depending on the load and power factor of the receiver.]

[Illustration: FIG. 2,682.--Capacity effect in a three phase
transmission line. It is the same as would be produced by shunting
the line at each point by three infinitesimal condensers connected in
star with the neutral point grounded, the capacity of each condenser
being twice that of a condenser of infinitesimal length formed by
any two of the wires. The effect of capacity on the regulation and
efficiency of the line can be determined with sufficient accuracy
in most cases by considering the line shunted at each end by three
condensers connected in star, the capacity of each condenser being
equal to that formed by any two wires of the line. An approximate
value for the charging current per wire is the current required to
charge a condenser, equal in capacity to that of any two of the
wires, to the pressure at the generating end of the line between any
one wire and the neutral point.]


     The self inductance of lines is readily calculated from the
   following formula:

  L = .000558 {2.303 log (2A ÷ _d_) + .25} per mile of circuit

where

   L = inductance of a loop of a three phase circuit in henrys.
       _Note._--The inductance of a complete single phase
                    circuit = L × 2 ÷ √3.
   A = distance between wires;
  _d_ = diameter of wire.


  CAPACITY IN MICRO-FARADS PER MILE OF CIRCUIT
            FOR THREE PHASE SYSTEM

  ---------+-------+----------+--------------
           | Diam. | Distance |   Capacity
    Size   |  in   |   A in   |     C in
   B. & S. | inch. |  inches. | micro-farads
  ---------+-------+----------+--------------
    0000   | .46   |    12    |    .0226
           |       |    18    |    .0204
           |       |    24    |    .01922
           |       |    48    |    .01474
           |       |          |
     000   | .41   |    12    |    .0218
           |       |    18    |    .01992
           |       |    24    |    .01876
           |       |    48    |    .01638
           |       |          |
      00   | .365  |    12    |    .0124
           |       |    18    |    .01946
           |       |    24    |    .01832
           |       |    48    |    .01604
           |       |          |
       0   | .325  |    12    |    .02078
           |       |    18    |    .01898
           |       |    24    |    .01642
           |       |    48    |    .01570
           |       |          |
       1   | .289  |    12    |    .02022
           |       |    18    |    .01952
           |       |    24    |    .01748
           |       |    48    |    .0154
           |       |          |
       2   | .258  |    12    |    .01972
           |       |    18    |    .01818
           |       |    24    |    .01710
           |       |    48    |    .01510
           |       |          |
       3   | .229  |    12    |    .01938
           |       |    18    |    .01766
           |       |    24    |    .01672
           |       |    48    |    .01480
           |       |          |
       4   | .204  |    12    |    .01874
           |       |    18    |    .01726
           |       |    24    |    .01636
           |       |    48    |    .01452
           |       |          |
       5   | .182  |    12    |    .01830
           |       |    18    |    .01690
           |       |    24    |    .01602
           |       |    48    |    .01426
           |       |          |
       6   | .162  |    12    |    .01788
           |       |    18    |    .01654
           |       |    24    |    .01560
           |       |    48    |    .0140
           |       |          |
       7   | .144  |    12    |    .01746
           |       |    18    |    .01618
           |       |    24    |    .01538
           |       |    48    |    .01374
           |       |          |
       8   | .128  |    12    |    .01708
           |       |    18    |    .01586
           |       |    24    |    .01508
           |       |    48    |    .01350
           |       |          |
       9   | .114  |    12    |    .01660
           |       |    18    |    .01552
           |       |    24    |    .01478
           |       |    48    |    .01326
           |       |          |
      10   | .102  |    12    |    .01636
           |       |    18    |    .01522
           |       |    24    |    .01452
           |       |    48    |    .01304
  ---------+-------+----------+--------------

=Capacity.=--In any given system of electrical conductors, a
pressure difference between two of them corresponds to the presence
of a quantity of electricity on each. With the same charges, the
difference of pressure may be varied by varying the geometrical
arrangement and magnitudes and also by introducing various
dielectrics. The constant connecting the charge and the resulting
pressure is called the capacity of the system.

     All circuits have a certain capacity, because each conductor
   acts like the plate of a condenser, and the insulating medium,
   acts as the dielectric. The capacity depends upon the insulation.

     For a given grade of insulation, the capacity is proportional
   to the surface of the conductors, and universally to the distance
   between them.

     A three phase three wire transmission line spaced at the corners
   of an equilateral triangle as regards capacity acts precisely
   as though the neutral line were situated at the center of the
   triangle.

     The capacity of circuits is readily calculated by applying the
   following formulae:

  C = 38.83 sc 10^{-3} / log (D ÷ d) per mile,
         insulated cable with lead sheath;
  C = 38.83 × 10^{-3} / log (4h ÷ d) per mile,
         single conductor with earth return;
  C = 19.42 × 10^{-3} / log (2A ÷ d) per mile of
         parallel conductors forming metallic circuit;

     in which

     C = Capacity in micro-farads; for a metallic circuit, C =
   capacity between wires;

     sc = Specific inductive capacity of insulating material; = 1 for
   air, and 2.25 to 3.7 for rubber;

     D = Inside diameter of lead sheath;
     d = Diameter of conductor;
     h = Distance of conductors above ground;
     A = Distance between wires.

=Frequency.=--The number of cycles per second, or the frequency,
has a direct effect upon the inductance reactance in an alternating
current circuit, as is plainly seen from the formula.

          X_{i} = 2π_f_L

     In the case of a transmission line alone; the lower frequencies
   are the more desirable, in that they tend to reduce the inductance
   drop and charging current. The inductance drop is proportional to
   the frequency.

     The natural period of a line, with distributed inductance and
   capacity, is approximately given by
               __
  P = 7,900 / √LC

     where L is the total inductance in millihenrys, and C, the total
   capacity in micro-farads. Accordingly some lower odd harmonic of
   the impressed frequency may be present which corresponds with the
   natural period of the line. When this obtains, oscillations of
   dangerous magnitude may occur. Such coincidences are less likely
   with the lower harmonics than with the higher.

=Skin Effect.=--The tendency of alternating current to confine itself
to the _outer_ portions of a conductor, instead of passing uniformly
through the cross section, is called _skin effect_. The effect is
proportional to the size of the conductor and the frequency.

=Ques. What effect has "skin effect" on the current?=

Ans. It is equivalent to an increase of ohmic resistance and
therefore opposes the current.

[Illustration: FIGS. 2,683 to 2,687.--Skin effect and shield effect.
Fig. 2,683, section of conductor illustrating skin effect or tendency
of the alternating current to distribute itself unequally through the
cross section of a conductor as shown by the varied shading, which
represents the current flowing most strongly in the outer portions
of the conductor. For this reason it has been proposed to use hollow
or flat instead of solid round conductors; however, with frequency
not exceeding 100, the skin effect is negligibly small in copper
conductors of the sizes usually employed. In figs. 2,684 and 2,685,
or 2,686 and 2,687, if two adjacent conductors be carrying current
in the same direction, concentration will occur on those parts of
the two conductors remote from one another, and the nearer parts
will have less current, that is to say, they will be =shielded=.
In this case, the induction due to one conductor will exert its
opposing effect to the greatest extent on those parts of the other
conductor nearest to it; this effect decreasing the deeper the latter
is penetrated. After crossing the current axis, the induction will
still decrease in magnitude, but will now aid the current in the
conductor. Hence, the effect of these two conductors on one another
will make the current density more uniform than is the case where
the two conductors adjacent to one another are carrying current in
opposite directions, as in figs. 2,685 and 2,686, therefore, the
resistance and the heating for a given current will be smaller. If
the two return conductors be situated on the line passing through
the center of the conductors just considered, the effect will be to
still further concentrate the current; the distribution symmetry will
be further disturbed, and the resistance of the conductor system
increased. It is therefore difficult to say which of the two cases
considered holds the advantage so far as increasing the resistance is
concerned. The case, however, in which the phases are mixed has much
the smaller reactive drop.]

     If the conductor be large, or the frequency high, the central
   portion of the conductor carries little if any current, hence the
   resistance is therefore greater for alternating current than for
   direct current.

=Ques. For what condition may "skin effect" be neglected?=

Ans. For frequencies of 60 or less, with conductors having a diameter
not greater than 0000 B. & S. gauge.

=Ques. How is the "skin effect" calculated for a given wire?=

Ans. Its area in circular mils multiplied by the frequency, gives the
ratio of the wire's ohmic resistance to its combined resistance.

     That is to say, the factor thus obtained multiplied by the
   resistance of the wire to direct current will give its combined
   resistance or resistance to alternating current.

     The following table gives these ratio factors for large
   conductors.

          RATIO FACTOR FOR COMBINED RESISTANCE

  +---------------+---------+---------------+---------+
  |  Cir. mils.   |  Ratio  |  Cir. mils.   |  Ratio  |
  |  × frequency  |  factor |  × frequency  |  factor |
  +---------------+---------+---------------+---------+
  |   10,000,000  |  1.00   |   70,000,000  |  1.13   |
  |   20,000,000  |  1.01   |   80,000,000  |  1.17   |
  |   30,000,000  |  1.03   |   90,000,000  |  1.20   |
  |   40,000,000  |  1.05   |  100,000,000  |  1.25   |
  |   50,000,000  |  1.08   |  125,000,000  |  1.34   |
  |   60,000,000  |  1.10   |  150,000,000  |  1.43   |
  +---------------+---------+---------------+---------+

=Corona Effect.=--When two wires, having a great difference of
pressure are placed near each other, a certain phenomenon occurs,
which is called _corona effect_. When the spacing or distance
between the wires is small and the difference of pressure in the
wires very great, a continuous passage of energy takes place through
the dielectric or atmosphere, the amount of this energy may be an
appreciable percentage of the power transmitted. Therefore in laying
out high pressure transmission lines, this effect must be considered
in the spacing of the wires.

=Ques. How does the corona effect manifest itself?=

Ans. It is visible at night as a bluish luminous envelope and audible
as a hissing sound.

=Ques. What is the critical voltage?=

Ans. The voltage at which the corona effect loss takes place.

=Ques. Upon what does the critical voltage depend?=

Ans. Upon the radius of the wires, the spacing, and the atmospheric
conditions.

[Illustration: FIG. 2,688.--Electromagnetic and electrostatic
fields surrounding the conductors of a transmission line. The
electromagnetic field is represented by lines of magnetic force
that surround the conductors in circles, (the solid lines), and
the electrostatic field by (dotted) circles passing from conductor
to conductor across at right angles to the magnetic circles. For
any given size of wire and distance apart of wires there is a
certain voltage at which the critical density or critical gradient
is reached, where the air breaks down and luminosity begins--the
critical voltage where corona manifests itself. At still higher
voltages corona spreads to further distances from the conductor
and a greater volume of air becomes luminous. Incidentally, it
produces noise. Now to produce light requires power and to produce
noise requires power. Air is broken down and is heated in breaking
down, and to heat also requires power; therefore, as soon as corona
forms, power is consumed or dissipated in its formation. When this
phenomenon occurs on the conductors of an alternating current circuit
a change takes place in relation to current and voltage. On the
wires of an alternating current transmission line, at a voltage
below that where corona forms--at a voltage where wires are not
luminous--considerable current, more or less depending on voltage
and length of wire, flows into the circuit as capacity current or
charging current.]

     The critical voltage increases with both the diameter of the
   wires, and the spacing.

     The losses due to corona effect increase very rapidly with
   increasing pressure beyond the critical voltage.

     The magnitude of the losses as well as the critical voltage is
   affected, by atmospheric conditions, hence they probably vary with
   the particular locality, and the season of the year. Therefore,
   for a given locality, a voltage which is normally below the
   critical point, may at times be above it, depending upon changes
   in the weather.

     Such elements as smoke, fog, moisture, or other particles (dust,
   snow, etc.) floating in the air, increase the losses; rain,
   however, apparently has no appreciable effect upon the losses.
   It follows then that in the design of a transmission line, the
   atmospheric conditions of the particular locality through which
   the line passes should be considered.

=Ques. How should live wires be spaced?=

Ans. They should be so spaced as to lessen the tendency to leakage
and to prevent the wires swinging together or against towers. The
spacing should be only sufficient for safety, since increased spacing
increases the self-induction of the line, and while it lessens the
capacity, it does so only in a slight degree.

     The following spacing is in accordance with average practice.

  SPACING FOR VARIOUS VOLTAGES

     +---------+----------+
     |  Volts  | Spacing  |
     +---------+----------+
     |   5,000 |  28 ins. |
     |  15,000 |  40 ins. |
     |  30,000 |  48 ins. |
     |  45,000 |  60 ins. |
     |  60,000 |  60 ins. |
     |  75,000 |  84 ins. |
     |  90,000 |  96 ins. |
     | 105,000 | 108 ins. |
     | 120,000 | 120 ins. |
     +---------+----------+

=Resistance of Wires.=--For quick calculation the following method
of obtaining the resistance (approximately) of wires will be found
convenient:

1,000 feet No. 10 B. & S. wire, which is about .1 inch in diameter
(.1019), has a resistance of one ohm, at a temperature of 68° F. and
weighs 31.4 pounds. A wire three sizes larger, that is No. 7, has
twice the cross section and therefore one-half the resistance. A wire
three sizes smaller than No. 10, that is No. 13, has one-half the
cross section and therefore twice the resistance.

Thus, starting with No. 10, any number three sizes larger will double
the cross sectional area and any wire three sizes smaller will halve
the cross sectional area of the preceding wire. This is true to the
extreme limits of the table, so that the area, weight and resistance
of any wire may be at once calculated to a close approximation from
this rule, intermediate sizes being obtained by interpolation.

For alternating current, the combined resistance, that is, the total
resistance, including skin effect, is obtained by multiplying the
resistance, as found above by the "ratio factor" (see table page
1,894).

[Illustration: FIGS. 2,689 to 2,692.--Triangles for obtaining
graphically, impedance, impressed pressure, etc., in alternating
current circuits. For a full explanation of this method the reader is
referred to Guide 5, Chapter XLVII on Alternating Current Diagrams. A
thorough study of this chapter is recommended.]

=Impedance.=--_The total opposition to the flow of electricity in an
alternating current circuit_, or the impedance may be resolved into
two components representing the ohmic resistance and the spurious
resistance; these components have a phase difference of 90°, and
they may be represented graphically by the two legs of a right angle
triangle, of which the hypothenuse represents the impedance.

Similarly, the volts lost or "drop" in an alternating circuit may be
resolved into two components representing respectively

1. The loss due to resistance.

2. The loss due to reactance.

These components have a phase difference of 90° and are represented
graphically similar to the impedance components. This has been
explained at considerable length in Chapter XLVII (Guide V).

[Illustration: FIG. 2,693.--Mechanical analogy of power factor, as
exemplified by a locomotive "poling" a car off a siding. The car and
locomotive are shown moving in parallel directions, and the pole
AB, inclined at an angle ϕ. Now, if the length of AB be taken to
represent the pressure exerted on the pole by the locomotive, then
the imaginary lines AC and BC, drawn respectively parallel and at
right angles to the direction of motion will represent respectively
the useful and no energy (wattless) components; that is to say, if
the pressure AB be applied to the car at an angle ϕ, only part of it,
AC, is useful in propelling the car, the other component, BC, being
wasted in tending to push the car off the track at right angles to
the rails, being resisted by the flanges of the outer wheels.]

=Power Factor.=--When the current falls out of step with the
pressure, as on inductive loads, the power factor becomes less than
unity, and the effect is to increase the current required for a
given load. Accordingly, this must be considered in calculating the
size of the wires. As has been explained, the current flowing in
an alternating current circuit, as measured by an ammeter, can be
resolved into two components, representing respectively the _active
component_ and the _wattless component_ or idle current. These are
graphically represented by the two legs of a right triangle, of which
the hypothenuse represents the current measured by the ammeter.

This _apparent_ current, as is evident from the triangle, exceeds
the _active_ current and lags behind the pressure by an amount
represented by the angle ϕ between the hypothenuse and leg
representing the energy current as shown in fig. 2,694.

[Illustration: FIG. 2,694.--Diagram showing that the apparent current
is more than the active current, the excess depending upon the angle
of phase difference.]

[Illustration: FIG. 2,695.--Diagram showing components of impedance
volts. Compare this diagram with figs. 2,689 and 2,671, and note that
the term "reactance" is the difference between the inductance drop
and the capacity drop if the circuit contain capacity, for instance,
if inductance drop be 10 volts and capacity drop be 7 volts then
reactance 10-7 = 3 volts.]

=Ques. What determines the heating of the wires on alternating
current circuits with inductive loads?=

Ans. The apparent current, as represented by the hypothenuse of the
triangle in fig. 2,694.

=Ques. How is the apparent current obtained?=

Ans. Divide the true watts by the product of the power factor
multiplied by the voltage.

     Example.--A certain circuit supplies 20 kw. to motors at 220
   volts and .8 power factor. What is the apparent current?

                          true watts         20,000
  Apparent Current = -------------------- = -------- = 113.6 amperes
                     power factor × volts   .8 × 220

=Ques. What else, besides power factor, should be considered in
making wire calculations for motor circuits?=

Ans. The efficiency of the motor, and the heavy starting current.

     The product of the efficiency of the motor multiplied by the
   power factor gives the _apparent efficiency_, which governs the
   size of the wires, apparatus, etc., necessary to feed the motors.

     Allowance should be made for the heavy starting current required
   for some motors to avoid undue drop.

           TABLE OF APPROXIMATE AMPERES PER TERMINAL
                    FOR INDUCTION MOTORS

  Column headings:  A-110 volts  B-220 volts  C-440 volts  D-550 volts

  +-----+----------------+------------------+------------------------+
  |     |                |    Two phase     |      Three phase       |
  |Horse|  Single phase  |    four wire     |      three wire        |
  |power+----+-----+-----+-----+-----+------+-----+-----+------+-----+
  |     | A  |  B  |  C  |  A  |  B  |  C   |  A  |  B  |  C   |  D  |
  +-----+----+-----+-----+-----+-----+------+-----+-----+------+-----+
  |   .5| 6.6| 3.4 |  1.8| 3.3 | 1.7 |   .9 | 3.7 | 1.8 |  1   |     |
  |   1 | 14 | 7   |  3.5| 6.4 | 3.2 |  1.6 | 7.4 | 3.7 |  1.9 |     |
  |   2 | 24 | 12  |  6  |  11 | 5.7 |  2.9 |  13 | 6.6 |  3.3 | 2.5 |
  |   3 | 34 | 17  |  8.5|  16 | 8.1 |  4.1 |  19 | 9.3 |  4.7 | 3.5 |
  |   4 | 52 | 26  | 13  |  26 |  13 |  6.5 |  30 |  15 |  7.5 |   6 |
  |   5 | 74 | 37  | 18.5|  38 |  19 |  9.5 |  44 |  22 | 11   |   9 |
  |  10 | 94 | 47  | 23.5|  44 |  22 | 11   |  50 |  25 | 12.5 |  11 |
  |  15 |    |     |     |  66 |  33 | 16.5 |  76 |  38 | 19   |  16 |
  |  20 |    |     |     |  88 |  44 | 22   | 102 |  51 | 25.5 |  22 |
  |  25 |    |     |     | 111 |  55 | 28   | 129 |  64 | 32   |  25 |
  |  30 |    |     |     | 134 |  67 | 33.5 | 154 |  77 | 38.5 |  32 |
  |  40 |    |     |     | 178 |  89 | 44.5 | 204 | 107 | 53.5 |  44 |
  |  50 |    |     |     | 204 | 102 | 51   | 236 | 118 | 59   |  52 |
  |  75 |    |     |     | 308 | 154 | 77   | 356 | 178 | 89   |  77 |
  | 100 |    |     |     | 408 | 204 | 102  | 472 | 236 | 118  | 100 |
  +-----+----+-----+-----+-----+-----+------+-----+-----+------+-----+

=Ques. What are the usual power factors encountered on commercial
circuits?=

Ans. A mixed load of incandescent lamps and induction motors will
have a power factor of from .8 to .85; induction motors above .8 to
.85; incandescent and Nernst lamps .98; arc lamps, .85.

=Wire Calculations.=--In the calculation of alternating current
circuits, the two chief factors which make the computation different
from that for direct current circuits, is _induction_ and _power
factor_. The first depends on the frequency, and physical condition
of the circuit, and the second upon the character of the load.

=Ques. Under what conditions may inductance be neglected?=

[Illustration: FIGS. 2,696 to 2,698.--Example of wiring showing where
inductance is negligible, and where it must be considered in wire
calculations.]

Ans. In cases where the wires of a circuit are not spaced over an
inch apart, or in conduit work, where both wires are in the same
conduit.

     Under these conditions the calculation is the same as for direct
   current after making proper allowance for power factor.

=Ques. Under what conditions must induction be considered?=

Ans. On exposed circuits with wires separated several inches,
particularly in the case of large wires.

=Sizes of Wire.=--The size of wire for any alternating circuit may be
determined by slightly modifying the formula used in direct current
work, and which, as derived in Guide No. 4, page 748, is

                  amperes × feet × 21.6
  circular mils = ---------------------  (1)
                            drop

     The quantity 21.6, is twice the resistance (10.8) of a foot of
   copper wire one mil in diameter (_mil foot_). This resistance
   (10.8) is multiplied by 2, giving the quantity 21.6, because the
   length of a circuit, or feet in the formula, is given as the "run"
   or distance one way, that is, one-half the total length of wire in
   the circuit, must be multiplied by 2 to get the total drop, viz.:

                  amperes × feet × 10.8 × 2   amperes × feet × 21.6
  circular mils = ------------------------- = ---------------------
                             drop                       drop

It is sometimes however convenient to make the calculation in terms
of watts. Formula (1) may be modified for such calculation.

In modifying the formula, the "drop" should be expressed in
percentage instead of actual volts lost, that is, instead of the
difference in pressure between the beginning and the end of the
circuit.

In any circuit the loss in percentage, or

                  drop
  % loss = ------------------ × 100
           impressed pressure

from which

         % loss × impressed pressure
  drop = ---------------------------  (2)
                     100

Substituting equation (2) in equation (1)

                      amperes × feet × 21.6
  circular mils = -----------------------------
                     % loss × imp. pressure
                    ------------------------
                              100

                    amperes × feet × 2,160
                = --------------------------  (3)
                    % loss × imp. pressure

Equation (3) is modified for calculation in terms of watts as
follows: The power in watts is equal to the _applied voltage_
multiplied by the current, that is to say, the power is equal to
the _volts at the consumer's end of the circuit_ multiplied by the
current, or simply

  watts = volts × amperes

from which

            watts
  amperes = -----  (4)
            volts

[Illustration: FIGS. 2,699 to 2,703.--Stranded copper cables. For
conductors of large areas and in the smaller sizes where extra
flexibility is required it becomes necessary to employ stranded
cables made by grouping a number of wires together in either
concentric or rope form. The concentric cable as here illustrated is
formed by grouping six wires around a central wire thereby forming
a seven wire cable. The next step is the application in a reverse
direction of another layer of 12 wires and a nineteen wire cable is
produced. This is again increased by a third layer of eighteen wires
for a 37 wire cable and a fourth layer of 24 wires for a 61 wire
cable. Successive layers, each containing 6 more wires than that
preceding, may be applied until the desired capacity is obtained. The
cuts show sectional views of concentric cables each formed from No.
10 B. & S. gauge wires.]

Substituting this value for the current in equation (3) and
remembering that the pressure taken is the volts at the consumer's
end of the line

                  watts
                  -----  × feet × 2,160
                  volts
  circular mils = ---------------------
                  % loss × volts

                  watts × feet × 2,160
                = --------------------    (5)
                   % loss × volts^{2}

This formula (5) applies to a direct current two wire circuit, and to
adapt it to any alternating current circuit it is only necessary to
use the letter M instead of the number 2,160, thus

                    watts × feet × M
  circular mils =  ------------------  (6)
                   % loss × volts^{2}

in which M is a coefficient which has various values according to the
kind of circuit and value of the power factor. These values are given
in the following table:

                          =VALUES OF M=

  --------+-----------------------------------------------------------
          |                     POWER FACTOR
   SYSTEM +-----+-----+-----+-----+-----+-----+-----+-----+-----+-----
          | 1.00|  .98|  .95|  .90|  .85|  .80|  .75|  .70|  .65|  .60
  --------+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----
   Single |2,160|2,249|2,400|2,660|3,000|3,380|3,840|4,400|5,112|6,000
    phase |     |     |     |     |     |     |     |     |     |
  --------+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----
    Two   |1,080|1,125|1,200|1,330|1,500|1,690|1,920|2,200|2,556|3,000
   phase  |     |     |     |     |     |     |     |     |     |
  (4 wire)|     |     |     |     |     |     |     |     |     |
  --------+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----
   Three  |1,080|1,125|1,200|1,330|1,500|1,690|1,920|2,200|2,556|3,000
   phase  |     |     |     |     |     |     |     |     |     |
  (3 wire)|     |     |     |     |     |     |     |     |     |
  --------+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----

            NOTE.--The above table is calculated as
          follows: For =single phase= M = 2,160 ÷ power
          factor^{2} × 100; for =two phase= four wire, or
          three phase three wire, M = ½ (2,160 ÷ power
          factor^{2})× 100. Thus the value of M for a
          single phase line with power factor .95 = 2,160 ÷
          .95^{2} × 100 = 2,400.

It must be evident that when 2,160 is taken as the value of M,
formula (6) applies to a two wire direct current circuit and also to
a single phase alternating current circuit when the power factor is
unity.

In the table the value of M for any particular power factor is found
by dividing 2,160 by the square of that power factor for single phase
and twice the square of the power factor for two phase and three
phase.

=Ques. For a given load and voltage how do the wires of a single and
two phase system compare in size and weight, the power factor being
the same in each case?=

Ans. Since the two phase system is virtually two single phase
systems, the four wires of the two phase systems are half the size of
the two wires of the single phase system, and accordingly, the weight
is the same for either system.

                       =VALUES OF T=

  +-------------------+--------------------------------------------+
  |                   |                POWER FACTOR                |
  |      SYSTEM       +--------+--------+--------+--------+--------+
  |                   |  1.00  |   .98  |   .90  |   .80  |   .70  |
  +-------------------+--------+--------+--------+--------+--------+
  |   Single phase    |  1.00  |   .98  |   .90  |   .80  |   .70  |
  +-------------------+--------+--------+--------+--------+--------+
  | Two phase, 4 wire |  2.00  |  1.96  |  1.80  |  1.60  |  1.40  |
  +-------------------+--------+--------+--------+--------+--------+
  |Three phase, 3 wire|  1.73  |  1.70  |  1.55  |  1.38  |  1.21  |
  +-------------------+--------+--------+--------+--------+--------+

            NOTE.--This table is for finding the value
          of the current in line, using the formula I =
          W ÷ (E × T), in which I = current in line; E =
          voltage between main conductors at receiving or
          consumers' end; W = watts. For instance, what
          is the current in a two phase line transmitting
          1,000 watts at 550 volts, power factor .80? I =
          1,000 ÷ (550 × 1.60) = 1.13.

=Ques. Since there is no saving in copper in using two phases, what
advantage has the two phase system over the one phase system?=

Ans. It is more desirable on power circuits, because two phase motors
are self-starting.

     That is to say, the rotating magnetic field that can be
   produced by a two phase current, permits an induction motor to
   start without being equipped with any special phase splitting
   devices which are necessary on single phase motors, because the
   oscillating field produced by a single phase current does not
   produce any torque on a squirrel cage armature at rest.

=Ques. For equal working conditions, what is the comparison between
the single, two and three phase system as to size and weight of
wires?=

Ans. Each wire of the three phase system is half the size of one of
the wires of the single phase system, hence the weight of copper
required for the three phase system is 75% of that required for the
single phase system. Since in the two phase system half of the load
is carried by each phase, each wire of the three phase system is the
same size as one of the wires of the two phase system, hence, the
copper required by the three phase system is 75% of that required by
the two phase system.

          =MISCELLANEOUS FORMULÆ FOR COPPER WIRES=

  Diameter squared                            = circular mils
  Circular mils          × .7854              = square mils
          .000003027     × circular mils      = pounds per foot
          .003027        × circular mils      = pounds per 1,000 feet
          .0159847       × circular mils      = pounds per mile
          .003879        × square mils        = pounds per 1,000 feet
          .33033         ÷ circular mils      = feet per pound
          .0000002924    × circular mils      = pounds per ohm
          .342           ÷ circular mils      = ohms per pound
          .096585        × circular mils      = feet per ohm
        10.353568        ÷ circular mils      = ohms per foot

Breaking weight of wire ÷ area = breaking weight per square inch.

Breaking weight per square inch × area = breaking weight of wire.

The weight of copper wire is 1-1/7 times the weight of iron wire of
same diameter.

     EXAMPLE.--What size wires must be used on a single phase circuit
   2,000 feet in length to supply 30 kw. at 220 volts with loss of
   4%, the power factor being .9?

     The formula for circular mils is

                   watts × feet × M
  circular mils = ------------------     (1)
                  % loss × volts^{2}

     Substituting the given values and the proper value of M from the
   table, in (1)

                  30,000 × 2,000 × 2,660
  circular mils = ---------------------- = 82,438
                       4 × 220^{2}

     Referring to the accompanying table of the properties of copper
   wire, the nearest _larger_ size wire is No. 1 B. & S. gauge having
   an area of 83,690 circular mils.


            =TABLE OF THE PROPERTIES OF COPPER WIRE=

     Giving weights, length and resistances of wires of Matthiessen's
   Standard Conductivity for both B. & S. G. (Brown & Sharpe Gauge)
   and B. W. G. (Birmingham Wire Gauge) from Transactions October
   1903, of the American Institute of Electrical Engineers.

    __________________________________________________________________
                                         |         |        |
      Gauges. To the nearest fourth      |         | Length.|Resistance.
            significant digit.           |         |        |
    _____________________________________|         |________|_________
          |       |           |          | Weight. |        |
          |       | Diameter. | Area.    |   Lbs.  |  Feet  | Ohms per
          |       |           |          |   per   | per lb.|1,000 ft.
    ______|_______|___________|__________|  1,000  |________|__________
          |       |           |          |  feet.  |        |
          |       |           | Circular |         |        |
    B.& S.| B.W.G.|  Inches.  |  mils.   |         |        | @ 68° F.
    ______|______ |___________|__________|_________|________|_________
          |       |           |          |         |        |
     0000 |       |  0.460    |  211,600 |  640.5  |  1.561 | .04893
          |  0000 |  0.454    |  206,100 |  623.9  |  1.603 | .05023
          |   000 |  0.425    |  180,600 |  546.8  |  1.829 | .05732
          |       |           |          |         |        |
     000  |       |  0.4096   |  167,800 |  508.0  |  1.969 | .06170
          |    00 |  0.380    |  144,400 |  437.1  |  2.288 | .07170
      00  |       |  0.3648   |  133,100 |  402.8  |  2.482 | .07780
          |       |           |          |         |        |
          |     0 |  0.340    |  115,600 |  349.9  |  2.858 | .08957
       0  |       |  0.3249   |  105,500 |  319.5  |  3.130 | .09811
          |     1 |  0.3000   |   90,000 |  272.4  |  3.671 | .1150
          |       |           |          |         |        |
       1  |       |  0.2893   |   83,690 |  253.3  |  3.947 | .1237
          |     2 |  0.2840   |   80,660 |  244.1  |  4.096 | .1284
          |     3 |  0.2590   |   67,080 |  203.1  |  4.925 | .1543
          |       |           |          |         |        |
       2  |       |  0.2576   |   66,370 |  200.9  |  4.977 | .1560
          |     4 |  0.2380   |   56,640 |  171.5  |  5.832 | .1828
       3  |       |  0.2294   |   52,630 |  159.3  |  6.276 | .1967
          |       |           |          |         |        |
          |     5 |  0.2200   |   48,400 |  146.5  |  6.826 | .2139
       4  |       |  0.2043   |   41,740 |  126.4  |  7.914 | .2480
          |     6 |  0.2030   |   41,210 |  124.7  |  8.017 | .2513
          |       |           |          |         |        |
      5   |       |  0.1819   | 33,100   |100.2    |  9.98  | .3128
          |     7 |  0.1800   | 32,400   | 98.08   | 10.20  | .3196
          |     8 |  0.1650   | 27,230   | 82.41   | 12.13  | .3803
          |       |           |          |         |        |
      6   |       |  0.1620   | 26,250   | 79.46   | 12.58  | .3944
          |     9 |  0.1480   | 21,900   | 66.30   | 15.08  | .4727
      7   |       |  0.1443   | 20,820   | 63.02   | 15.87  | .4973
          |       |           |          |         |        |
          |    10 |  0.1340   | 17,960   | 54.35   | 18.40  | .5766
      8   |       |  0.1285   | 16,510   | 49.98   | 20.01  | .6271
          |    11 |  0.1200   | 14,400   | 43.59   | 22.94  | .7190
          |       |           |          |         |        |
      9   |       |  0.1144   | 13,090   | 39.63   | 25.23  | .7908
          |    12 |  0.1090   | 11,880   | 35.96   | 27.81  | .8715
     10   |       |  0.1019   | 10,380   | 31.43   | 31.82  | .9972
          |       |           |          |         |        |
          |    13 |  0.0950   |  9,025   | 27.32   | 36.60  | 1.147
     11   |       |  0.09074  |  8,234   | 24.93   | 40.12  | 1.257
          |    14 |  0.08300  |  6,889   | 20.85   | 47.95  | 1.503
          |       |           |          |         |        |
     12   |       |  0.08081  |  6,530   | 19.77   | 50.59  | 1.586
          |    15 |  0.07200  |  5,184   | 15.69   | 63.73  | 1.997
     13   |       |  0.07196  |  5,178   | 15.68   | 63.79  | 1.999
          |       |           |          |         |        |
          |    16 |  0.06500  |  4,225   | 12.79   | 78.19  | 2.451
     14   |       |  0.06408  |  4,107   | 12.43   | 80.44  | 2.521
          |    17 |  0.0580   |  3,364   | 10.18   | 98.23  | 3.078
          |       |           |          |         |        |
     15   |       |  0.05707  |  3,257   |  9.858  | 101.4  | 3.179
     16   |       |  0.05082  |  2,583   |  7.818  | 127.9  | 4.009
          |    18 |  0.04900  |  2,401   |  7.268  | 137.6  | 4.312
          |       |           |          |         |        |
     17   |       |  0.045260 |  2,048   |  6.200  | 161.3  | 5.055
          |    19 |  0.042000 |  1,764   |  5.340  | 187.3  | 5.870
     18   |       |  0.040300 |  1,624   |  4.917  | 203.4  | 6.374
          |       |           |          |         |        |
     19   |       |  0.035890 |  1,288   |  3.899  | 256.5  | 8.038
          |    20 |  0.035000 |  1,225   |  3.708  | 269.7  | 8.452
          |    21 |  0.032000 |  1,024   |  3.100  | 322.6  | 10.11
          |       |           |          |         |        |
     20   |       |  0.031960 |  1,022   |  3.092  | 323.4  | 10.14
     21   |       |  0.028460 |    810.1 |  2.452  | 407.8  | 12.78
          |    22 |  0.028000 |    784.0 |  2.373  | 421.4  | 13.21
     22   |       |  0.025350 |    642.4 |  1.945  | 514.2  | 16.12
          |    23 |  0.025000 |    625.0 |  1.892  | 528.6  | 16.57
     23   |       |  0.022570 |    509.5 |  1.542  | 648.4  | 20.32
          |       |           |          |         |        |
          |    24 |  0.022000 |    484.0 |  1.465  | 682.6  | 21.39
     24   |       |  0.020100 |    404.0 |  1.223  | 817.6  | 25.63
          |    25 |  0.020000 |    400.0 |  1.211  | 825.9  | 25.88
          |       |           |          |         |        |
          |    26 |  0.018000 |    324.0 |  .9808  | 1,020  |  31.96
     25   |       |  0.017900 |    320.4 |  .9699  | 1,031  |  32.31
          |    27 |  0.016000 |    256.0 |  .7749  | 1,290  |  40.45
          |       |           |          |         |        |
     26   |       |  0.015940 |    254.1 |  .7692  | 1,300  |  40.75
     27   |       |  0.014200 |    201.5 |  .6100  | 1,639  |  51.38
          |    28 |  0.014000 |    196.0 |  .5933  | 1,685  |  52.83
          |       |           |          |         |        |
          |    29 |  0.013000 |    169.0 |  .5116  | 1,955  |  61.27
     28   |       |  0.012640 |    159.8 |  .4837  | 2,067  |  64.79
          |    30 |  0.012000 |    144.0 |  .4359  | 2,294  |  71.90
          |       |           |          |         |        |
     29   |       |  0.011260 |  126.7   |  .3836  | 2,607  |  81.70
     30   |       |  0.010030 |  100.5   |  .3042  | 3,287  | 103.0
          |    31 |  0.010000 |  100.0   |  .3027  | 3,304  | 103.5
          |       |           |          |         |        |
          |    32 |  0.009000 |   81.0   |  .2452  | 4,078  | 127.8
     31   |       |  0.008928 |   79.70  |  .2413  | 4,145  | 129.9
          |    33 |  0.008000 |   64.0   |  .1937  | 5,162  | 161.8
          |       |           |          |         |        |
     32   |       |  0.007950 |   63.21  |  .1913  | 5,227  | 163.8
     33   |       |  0.007080 |   50.13  |  .1517  | 6,591  | 206.6
          |    34 |  0.007000 |   49.0   |  .1483  | 6,742  | 211.3
          |       |           |          |         |        |
     34   |       |  0.006305 |   39.75  |  .1203  | 8,311  | 260.5
     35   |       |  0.005615 |   31.52  |  .09543 |10,480  | 328.4
     36   |    35 |  0.005000 |   25.0   |  .07568 |13,210  | 414.2
          |       |           |          |         |        |
     37   |       |  0.004453 |   19.83  |  .06001 |16,660  | 522.2
          |    36 |  0.004000 |   16.    |  .04843 |20,650  | 647.1
     38   |       |  0.003965 |   15.72  |  .04759 |21,010  | 658.5
          |       |           |          |         |        |
     39   |       |  0.003531 |   12.47  |  .03774 |26,500  | 830.4
     40   |       |  0.003145 |    9.888 |  .02993 |33,410  |1047.
  --------------------------------------------------------------------

=Drop.=--In order to determine the drop or volts lost in the line,
the following formula may be used

drop = ((% loss × volts) / 100) × S (1)

in which the % loss is a percentage of the applied power, that is,
the power delivered to the consumer and not a percentage of the power
at the alternator. "Volts" is the pressure at the consumer's end of
the circuit.

                     =VALUE OF "S" FOR 60 CYCLES=

  -----------------+------------------------+------------------------+
                   |   .98 power factor     |    .90 power factor    |
  --------+--------+------------------------+------------------------+
  Size of | Area   |   Spacing of           | Spacing of             |
   wire   |  in    |   conductors           | conductors             |
   B.&S.  |circular|                        |                        |
   gauge  | mils.  |                        |                        |
          |        +----+----+----+----+----+----+----+----+----+----+
          |        | 1" | 3" | 6" | 12"| 24"| 1" | 3" | 6" | 12"| 24"|
  --------+--------+----+----+----+----+----+----+----+----+----+----+
  500,000 |500,000 |1.21|1.45|1.61|1.77|1.92|1.32|1.80|2.11|2.44|2.75|
  300,000 |300,000 |1.15|1.29|1.38|1.48|1.57|1.19|1.47|1.66|1.84|2.02|
    0,000 |211,600 |1.12|1.22|1.28|1.34|1.41|1.13|1.33|1.45|1.58|1.63|
      000 |167,800 |1.09|1.18|1.22|1.28|1.29|1.08|1.23|1.33|1.44|1.53|
       00 |133,100 |1.07|1.14|1.18|1.21|1.25|1.03|1.16|1.24|1.32|1.40|
        0 |105,500 |1.05|1.10|1.14|1.17|1.20|1.00|1.09|1.16|1.22|1.28|
        1 | 83,690 |1.04|1.08|1.10|1.13|1.15|1.00|1.05|1.09|1.14|1.19|
        2 | 66,370 |1.02|1.05|1.08|1.10|1.12|1.00|1.00|1.04|1.08|1.12|
        3 | 52,630 |1.02|1.04|1.06|1.07|1.09|1.00|1.00|1.00|1.03|1.06|
          |        |    |    |    |    |    |    |    |    |    |    |
        4 | 41,740}|1.00|1.02|1.03|1.04|1.07|1.00|1.00|1.00|1.00|1.00|
        5 | 33,100}|    |    |    |    |    |    |    |    |    |    |
          |        |    |    |    |    |    |    |    |    |    |    |
        6 | 26,250}|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|
        7 | 20,820}|    |    |    |    |    |    |    |    |    |    |
          |        |    |    |    |    |    |    |    |    |    |    |
        8 | 16,510}|    |    |    |    |    |    |    |    |    |    |
        9 | 13,090}|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|
       10 | 10,380}|    |    |    |    |    |    |    |    |    |    |
  --------+--------+----+----+----+----+----+----+----+----+----+----+
  --------+--------+----+----+----+----+----+----+----+----+----+----+
   Size   |        |    .80 power factor    |    .70 power factor    |
    of    |  Area  +------------------------+------------------------+
   wire   |   in   |       Spacing of       |        Spacing of      |
   B.&S.  |circular|       conductors       |        conductors      |
   gauge  |  mils. +----+----+----+----+----+----+----+----+----+----+
          |        | 1" | 3" | 6" | 12"| 24"| 1" | 3" | 6" | 12"| 24"|
  --------+--------+----+----+----+----+----+----+----+----+----+----+
  500,000 | 500,000|1.27|1.89|2.25|2.64|3.03|1.14|1.72|2.12|2.53|2.92|
  300,000 | 300,000|1.11|1.46|1.68|1.90|2.12|1.00|1.33|1.56|1.78|2.01|
    0,000 | 211,600|1.03|1.27|1.43|1.58|1.75|1.00|1.14|1.29|1.45|1.69|
      000 | 167,800|1.00|1.16|1.28|1.41|1.53|1.00|1.02|1.15|1.28|1.50|
       00 | 133,100|1.00|1.07|1.15|1.22|1.00|1.00|1.00|1.03|1.13|1.21|
        0 | 105,500|1.00|1.00|1.07|1.15|1.00|1.00|1.00|1.00|1.01|1.09|
        1 | 83,690}|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|
        2 | 66,370}|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|
        3 | 52,630}|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|
          |        |    |    |    |    |    |    |    |    |    |    |
        4 | 41,740}|    |    |    |    |    |    |    |    |    |    |
        5 | 33,100}|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|
          |        |    |    |    |    |    |    |    |    |    |    |
        6 | 26,250}|    |    |    |    |    |    |    |    |    |    |
        7 | 20,820}|    |    |    |    |    |    |    |    |    |    |
          |        |    |    |    |    |    |    |    |    |    |    |
        8 | 16,510}|    |    |    |    |    |    |    |    |    |    |
        9 | 13,090}|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|
       10 | 10,380}|    |    |    |    |    |    |    |    |    |    |
  --------+--------+----+----+----+----+----+----+----+----+----+----+
The coefficient S has various values as given in the accompanying
tables. As will be seen from the table, the value of S to be used
depends upon the size of wire, spacing, power factor and frequency.

These values are accurate enough for all practical purposes, and may
be used for distances of 20 miles or less and for voltages up to
25,000.

The capacity effect on very long high voltage lines, makes this
method of determining the drop somewhat inaccurate beyond the limits
above mentioned.

                     =VALUE OF "S" FOR 25 CYCLES=

  ---------+--------+------------------------+------------------------+
    Size   |        |    .98 power factor    |    .90 power factor    |
     of    | Area   +------------------------+------------------------+
    wire   |  in    |       Spacing of       |       Spacing of       |
    B.&S.  |circular|       conductors       |       conductors       |
    gauge  | mils.  +----+----+----+----+----+----+----+----+----+----+
           |        | 1" | 2" | 6" | 12"| 24"| 1" | 3" | 6" | 12"| 24"|
  ---------+--------+----+----+----+----+----+----+----+----+----+----+
   500,000 |500,000 |1.01|1.17|1.23|1.29|1.36|1.02|1.22|1.35|1.43|1.61|
   300,000 |300,000 |1.04|1.10|1.13|1.18|1.21|1.00|1.08|1.16|1.25|1.31|
     0,000 |211,600 |1.03|1.07|1.09|1.11|1.14|1.00|1.02|1.07|1.13|1.15|
       000 |167,800 |1.00|1.05|1.06|1.09|1.10|1.00|1.00|1.02|1.07|1.11|
        00 |133,100 |1.00|1.03|1.05|1.06|1.08|1.00|1.00|1.00|1.02|1.05|
         0 |105,500 |1.00|1.01|1.02|1.03|1.04|1.00|1.00|1.00|1.00|1.00|
           |        |    |    |    |    |    |    |    |    |    |    |
         1 | 83,690}|    |    |    |    |    |    |    |    |    |    |
         2 | 66,370}|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|
         3 | 52,630}|    |    |    |    |    |    |    |    |    |    |
           |        |    |    |    |    |    |    |    |    |    |    |
         4 | 41,740}|    |    |    |    |    |    |    |    |    |    |
         5 | 33,100}|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|
         6 | 26,250}|    |    |    |    |    |    |    |    |    |    |
           |        |    |    |    |    |    |    |    |    |    |    |
         7 | 20,820}|    |    |    |    |    |    |    |    |    |    |
         8 | 16,510}|    |    |    |    |    |    |    |    |    |    |
         9 | 13,090}|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|
        10 | 10,380}|    |    |    |    |    |    |    |    |    |    |
  ---------+--------+----+----+----+----+----+----+----+----+----+----+
    Size   |        |    .80 power factor    |    .70 power factor    |
     of    |  Area  +------------------------+------------------------+
    wire   |   in   |       Spacing of       |        Spacing of      |
    B.&S.  |circular|       conductors       |        conductors      |
    gauge  |  mils. +----+----+----+----+----+----+----+----+----+----+
           |        | 1" | 3" | 6" | 12"| 24"| 1" | 3" | 6" | 12"| 24"|
  ---------+--------+----+----+----+----+----+----+----+----+----+----+
   500,000 | 500,000|1.00|1.15|1.30|1.47|1.62|1.00|1.00|1.16|1.33|1.49|
   300,000 | 300,000|1.00|1.00|1.09|1.16|1.25|1.00|1.00|1.00|1.02|1.12|
     0,000 | 211,600|1.00|1.00|1.00|1.03|1.10|1.00|1.00|1.00|1.00|1.00|
       000 | 167,800|1.00|1.00|1.00|1.00|1.01|1.00|1.00|1.00|1.00|1.00|
        00 | 133,100|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|
         0 | 105,500|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|
           |        |    |    |    |    |    |    |    |    |    |    |
         1 | 83,690}|    |    |    |    |    |    |    |    |    |    |
         2 | 66,370}|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|
         3 | 52,630}|    |    |    |    |    |    |    |    |    |    |
           |        |    |    |    |    |    |    |    |    |    |    |
         4 | 41,740}|    |    |    |    |    |    |    |    |    |    |
         5 | 33,100}|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|
         6 | 26,250}|    |    |    |    |    |    |    |    |    |    |
           |        |    |    |    |    |    |    |    |    |    |    |
         7 | 20,820}|    |    |    |    |    |    |    |    |    |    |
         8 | 16,510}|    |    |    |    |    |    |    |    |    |    |
         9 | 13,090}|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|
        10 | 10,380}|    |    |    |    |    |    |    |    |    |    |
  ---------+--------+----+----+----+----+----+----+----+----+----+----+

     EXAMPLE.--A circuit supplying current at 440 volts, 60
   frequency, with 5% loss and .8 power factor is composed of No. 2
   B. & S. gauge wires spaced one foot apart. What is the drop in the
   line?

     According to the formula

         % loss × volts
  drop = -------------- × S
               100

     Substituting the given values, and value of S as obtained from
   the table for frequency 60

         5 × 440
  drop = ------- × 1 = 22 volts
           100


=Current=.--As has been stated, the effect of power factor less than
unity, is to increase the current; hence, in inductive circuit
calculations, the first step is to determine the current flowing in a
circuit. This is done as follows:

                          apparent load
                current = -------------              (1)
                              volts

  and

                             watts
          apparent load = ------------               (2)
                          power factor

  Substituting (2) in (1)

                 watts
              ------------
              power factor          watts
    current = ------------ = ---------------------   (3)
                 volts       power factor × volts


[Illustration: FIG. 2,704.--Rope type of stranded copper cable
which is used when a high degree of flexibility is required. The
construction of this cable is the stranding together of seven groups,
each containing seven wires and producing a total of 49 wires.
In cases when a greater carrying capacity is desired than can be
obtained through the use of the 7 × 7 or 49 wire cable, the number of
groups is increased to nineteen thereby making a total of 133 wires
(19 × 7).]

     EXAMPLE.--A 50 horse power 440 volt motor has a full load
   efficiency of .9 and power factor of .8. How much current is
   required?

     Since the brake horse power of the motor is given, it is
   necessary to obtain the electrical horse power, thus

                  brake horse power   50
         E.H.P. = ----------------- = -- = 55.5
                     efficiency       .9

  which in watts is

                    55.5 × 746 = 41,403

  which is the actual load, and from which

                        actual load    41,403
       apparent load = ------------  = ------ = 51,754
                       power factor      .8

     The current therefore at 440 volts is

  apparent load   51,754
  ------------- = ------ = 117.6 amperes
      volts        440

     EXAMPLE.--A 50 horse power single phase 440 volt motor, having
   a full load efficiency of .92 and power factor of .8, is to be
   operated at a distance of 1,000 feet from the alternator. The
   wires are to be spaced 6 inches apart and the frequency is 60, and
   % loss 5. Determine: =A=, _electrical horse power_; =B=, _watts_;
   =C=, _apparent load_; =D=, _current_; =E=, _size of wires_; =F=,
   _drop_; =G=, _voltage at the alternator_.

     =A=. _Electrical horse power_

                  brake horse power    50
       E. H. P. = ----------------- × --- = 54.3
                     efficiency       .92

  or,

               54.3 × 746 = 40,508 watts

                =TABLE OF WIRE EQUIVALENTS=
                    (Brown and Sharpe gauge)
  ------+--------+--------+--------+---------+---------+---------
   0000 | 2 #  0 | 4 #  3 | 8 #  6 | 16 #  9 | 32 # 12 | 64 # 15
    000 | 2 "  1 | 4 "  4 | 8 "  7 | 16 " 10 | 32 " 13 | 64 " 16
     00 | 2 "  2 | 4 "  5 | 8 "  8 | 16 " 11 | 32 " 14 | 64 " 17
      0 | 2 "  3 | 4 "  6 | 8 "  9 | 16 " 12 | 32 " 15 | 64 " 18
      1 | 2 "  4 | 4 "  7 | 8 " 10 | 16 " 13 | 32 " 16 | 64 " 19
      2 | 2 "  5 | 4 "  8 | 8 " 11 | 16 " 14 | 32 " 17 | 64 " 20
      3 | 2 "  6 | 4 "  9 | 8 " 12 | 16 " 15 | 32 " 18 | 64 " 21
      4 | 2 "  7 | 4 " 10 | 8 " 13 | 16 " 16 | 32 " 19 | 64 " 22
      5 | 2 "  8 | 4 " 11 | 8 " 14 | 16 " 17 | 32 " 20 | 64 " 23
      6 | 2 "  9 | 4 " 12 | 8 " 15 | 16 " 18 | 32 " 21 | 64 " 24
      7 | 2 " 10 | 4 " 13 | 8 " 16 | 16 " 19 | 32 " 22 | 64 " 25
      8 | 2 " 11 | 4 " 14 | 8 " 17 | 16 " 20 | 32 " 23 | 64 " 26
      9 | 2 " 12 | 4 " 15 | 8 " 18 | 16 " 21 | 32 " 24 | 64 " 27
     10 | 2 " 13 | 4 " 16 | 8 " 19 | 16 " 22 | 32 " 25 | 64 " 28
     11 | 2 " 14 | 4 " 17 | 8 " 20 | 16 " 23 | 32 " 26 | 64 " 29
     12 | 2 " 15 | 4 " 18 | 8 " 21 | 16 " 24 | 32 " 27 | 64 " 30
     13 | 2 " 16 | 4 " 19 | 8 " 22 | 16 " 25 | 32 " 28 |
     14 | 2 " 17 | 4 " 20 | 8 " 23 | 16 " 26 | 32 " 29 |
     15 | 2 " 18 | 4 " 21 | 8 " 24 | 16 " 27 | 32 " 30 |
     16 | 2 " 19 | 4 " 22 | 8 " 25 | 16 " 28 |         |
     17 | 2 " 20 | 4 " 23 | 8 " 26 | 16 " 29 |         |
     18 | 2 " 21 | 4 " 24 | 8 " 27 | 16 " 30 |         |
     19 | 2 " 22 | 4 " 25 | 8 " 28 |         |         |
     20 | 2 " 23 | 4 " 26 | 8 " 29 |         |         |
     21 | 2 " 24 | 4 " 27 | 8 " 30 |         |         |
  ------+--------+--------+--------+---------+---------+---------

=B.= _Watts_

  watts = E.H.P. × 746 = 54.3 × 746 = 40,508

=C.= _Apparent load_

  apparent load or kva = (actual load or watts ÷ power factor)

                       = 40,508 ÷ .8 = 50,635

=D.= _Current_

  current = (apparent load or kva ÷ volts)
          = 50,635 ÷ 440
          = 115 amperes

=E.= _Size of wires_

  cir. mils = (watts × feet × M) ÷ (% loss × volts^{2})
            = (40,508 × 1,000 × 3,380) ÷ (5 × 440^{2})
            = 141,443

From table page 1,907, nearest size _larger_ wire is No. 00 B.&S.
gauge.

=F.= _Drop_

  drop = ((% loss × volts) ÷ 100) × S
       = ((5 × 440) ÷ 100) × 1.17
       = 25.74 volts

NOTE.--Values of S are given on page 1910.

=G.= _Voltage at alternator_

  alternator pressure = (volts at motor + drop)
                      = 440 + 25.74
                      = 465.7 volts.



CHAPTER LXVI

POWER STATIONS


The term _power station_ is usually applied to any building
containing an installation of machinery for the conversion of energy
from one form into another form. There are three general classes of
station:

  1. Central stations;
  2. Sub-stations;
  3. Isolated plants.

These may also be classified with respect to their function as

  1. Generating stations;
  2. Distributing stations;
  3. Converting stations.

and with respect to the form of power used in generating the electric
current, generating stations may be classed as

  1. Steam electric;
  2. Hydro-electric;
  3. Gas electric, etc.

=Central Stations.=--It must be evident that the general type of
central station to be adapted to a given case, that is to say, the
general character of the machinery to be installed depends upon the
kind of natural energy available for conversion into electrical
energy, and the character of the electrical energy required by the
consumers.

This gives rise to a further classification, as

  1. Alternating current stations;
  2. Direct current stations;
  3. Alternating and direct current stations.

The alternators or dynamos may be driven by steam or water turbines,
reciprocating engines, or gas engines, according to the character of
the natural energy available.

[Illustration: FIG. 2,705.--Elevation of small station with direct
drive, showing arrangement of the boiler and engine, piping, etc.]

=Ques. Why is the reciprocating engine being largely replaced by the
steam turbine, especially for large units?=

Ans. Because of its higher rotative speed, and absence of a
multiplicity of bearings which in the case of a high speed,
reciprocating engine must be maintained in close adjustment for the
proper operation of the engine.

     The higher speed of rotation results in a more compact unit,
   desirable for driving high frequency alternators.

=Ques. Is the steam turbine more economical than a high duty
reciprocating engine?=

Ans. No.

=Location of Central Stations.=--As a rule, central stations should
be so located that the average loss of voltage in overcoming the
resistance of the lines is a minimum, and this point is located
at the center of gravity of the system. In fig. 2,706 is shown a
graphical method of locating this important spot.

[Illustration: Fig. 2,706.--Diagram illustrating graphical method
of determining the _center of gravity_ of a system in locating the
central station.]

     Suppose a rough canvass of prospective consumers in a district
   to be supplied with electric light or power shows the principal
   loads to be located at A, B, C, D, E, etc., and for simplicity
   assume that these loads will be approximately equal, so that each
   may be denoted by 1 for example:

The relative locations of A, B, C, D, E, etc., should be drawn to
scale (say 1 inch to the 1,000 feet) after which the problem resolves
itself into finding the location of the station with respect to this
scale.

[Illustration: FIG. 2,707.--Exterior of central station at Lewis,
Ia.; example of very small station located in the principal business
section of a town. It also illustrates the use of a direct connected
gasoline electric set. The central station is located on Main Street,
which is the principal thoroughfare, and is installed in a low one
story building for which a mere nominal rental charge is paid, the
company having the option to buy the property later at the value of
the land plus the cost of the improvements and simple interest on
the same. To the front of an old frame building about 16 feet by
28 feet has been built a neat, well lighted concrete block room,
about 16 feet by 16 feet, carrying the building to the lot line and
affording ample space for the generating set and switchboards, and
such desk room as is needed for the ordinary office business of
the company. In this room, which is finished in natural pine with
plastered walls, has been installed a standard General Electric 25
kw. gasoline electric generating set consisting of a four cylinder,
four cycle, vertical water cooled, 43-54 H.P. gasoline engine, direct
connected to a three phase, 2,300 volt, 600 R.P.M. alternator with
a 125 volt exciter mounted on the same shaft and in the same frame.
With the generating set is a slate switchboard panel equipped with
three ammeters, one voltmeter, an instrument plug switch for voltage
indication, one single pole carbon break switch, one automatic oil
circuit breaker line switch and rheostats. Instrument transformers
are mounted above and back of the board. For street lighting service
a 4 kw. constant current transformer has been installed, and with
it a gray marble switchboard panel mounted on iron frames and
carrying an ammeter and a four point plug switch. On a board near
the generator set are mounted in convenient reach suitable wrenches,
spanners, and repair parts and tools. To cool the engine cylinders
five 6 × 8 steel tanks have been installed in the old building, a
pump on engine giving forced circulation.]

     The solution consists in first finding the center of gravity
   of any two of the loads, such as those at A and B. Since each of
   these is 1, they will together have the same effect on the system
   as the resultant load of 1 and 1, or 2, located at their center of
   gravity, this point being so chosen that the product of the loads
   by their respective distances from this point will in both cases
   be equal.

     The loads being equal in this case the distances must be equal
   in order that the products be the same, so that the center of
   gravity of A + B is at G, which point is midway between A and B.

     Considering, next, the resultant load of 2 at G and the load of
   1 at C, the resultant load at the center or gravity of these will
   be 3, and this must be situated at a distance of two units from C
   and one unit from G so that the distance 2 times the load 1 at C
   equals the distance 1 times the load 2 at G. Having thus located
   the load 3 at H, the same method is followed in finding the load 4
   at I. Then in like manner the resultant load 4 and the load 1 at E
   gives a load 5 at S.

     The point S being the last to be determined represents,
   therefore, the position of the center of gravity of the entire
   system, and consequently the proper position of the plant in order
   to give the minimum loss of voltage on the lines.

=Ques. Is the center of gravity of the system, as obtained in fig.
2,706, the proper location for the central station?=

Ans. It is very rarely the best location.

=Ques. Why?=

Ans. Other conditions, such as the price of land, difficulty of
obtaining water, facilities for delivery of coal and removal of
ashes, etc., may more than offset the minimum line losses and copper
cost due to locating the station at the center of gravity of the
system.

[Illustration: FIG. 2,708.--Map of Cia Docas de Santos hydro-electric
system; an example of station location remote from the center of
distribution. In the figure A is the intake; B, flume; C, forebay;
D, penstocks; E, power house; F, narrow gauge railway; G, general
store; H, point of debarkation; I, transmission line; J, dead ends;
K, sub-station. Santos, in the republic of Brazil, is one of the
great coffee shipping ports of the world, and for the development of
its water front has required an elaborate system of quays. These have
been developed by the Santos Dock Company, which holds a concession
for the whole water front. The company, needing electric power for
its own use, has developed a system deriving its power from a point
about thirty miles from the city, where a small stream plunges
down the sea coast from the mountain range that runs along it. The
engineers have estimated that 100,000 horse power can be obtained
from this source.]

=Ques. How then should the station be located?=

Ans. The more practical experience the designer has had, and the
more common sense he possesses, the better is he equipped to handle
the problem, as the solution is generally such that it cannot be
worked out by any rule of thumb method.

[Illustration: FIG. 2,709.--Station location. The figure shows
two distribution centers as a town A and suburb B supplied with
electricity from one station. For minimum cost of copper the location
of the station would be at G, the center of gravity. However, it is
very rarely that this is the best location. For instance at C, land
is cheaper than at G, and there is room for future extension to the
station, as shown by the dotted lines, whereas at G, only enough
land is available for present requirements. Moreover C is near the
railroad where coal may be obtained without the expense of cartage,
and being located at the river, the plant may be run condensing thus
effecting considerable economy. The conditions may sometimes be such
that any one of the advantages to be secured by locating the station
at C may more than offset the additional cost of copper.]

=Ques. What are the general considerations with respect to the price
of land?=

Ans. The cost for the station site may be so high as to necessitate
building or renting room at a considerable distance from the district
to be supplied.

     If the price of land selected for the station be high, the
   running expenses will be similarly affected, inasmuch as more
   interest must then be paid on the capital invested.

     The price or rent of real estate might also in certain
   instances alter the proposed interior arrangement of the station,
   particularly so in the case of a company with small capital
   operating in a city where high prices prevail. In general,
   however, it may be stated that whatever effect the price of real
   estate would have upon the arrangement, operation and location
   of a central station it can quite readily and accurately be
   determined in advance.

=Ques. With respect to the cost of the land what should be especially
considered?=

Ans. Room for the future extension of the plant.

     Although such additional space need not be purchased at the time
   of the original installation it is well, if possible, to make
   provision whereby it can be obtained at a reasonable figure when
   desired. The preliminary canvass of consumers will aid in deciding
   the amount of space advisable to allow for future extensions; as a
   rule, however, it is wise to count on the plant enlarging to not
   less than twice its original size, as often the dimensions have to
   be increased four and even six times those found sufficient at the
   beginning.

[Illustration: FIG. 2,710.--Section of the central station or
"electricity works" at Derby, showing boiler and engine room and
arrangement of bunkers, conveyor, ash pit, grates, boilers (drum,
heating surface and superheater), economizer, flue, turbines,
condenser pumps, etc.; also location of switchboard gallery and
system of piping.]

=Ques. What trouble is likely to be encountered with an illy located
plant after it is in operation?=

Ans. It may be considered a nuisance by those residing in the
vicinity, occasioning many complaints.

[Illustration: FIG. 2,711.--View of old and new Waterside stations.
The new station at the right has an all turbine equipment of ten
units, some Curtis and some Parsons machines, two have a capacity of
14,000 kw., and the remaining eight are of 12,000 kw. each. The old
Riverside station, seen at the left is described on page 1940.]

     Thus, if the plant be placed in a residential section of the
   community the smoke, noise and vibration of the machines may
   become a nuisance to the surrounding inhabitants, and eventually
   end in suits for damage against the company responsible for the
   same. For these and the other reasons just given a company is
   sometimes forced to disregard entirely the location of a central
   station near the center of gravity of the system, and build at a
   considerable distance; such a proceeding would, if the distance be
   great, necessitate the installation of a high pressure system.

     There might, however, be certain local laws in force restricting
   the use of high pressure currents on account of the danger
   resulting to life, that would prevent this solution of the
   problem. In such cases there could undoubtedly be found some site
   where the objections previously noted would be tolerated; thus,
   there would naturally be little objection to locating next to a
   stable, a brewery, or a factory of any description.

=Ques. Why is the matter of water supply important for a central
station?=

Ans. Because, in a steam driven plant, water is used in the boilers
for the production of steam by boiling, and if the engines be of the
condensing type it is also used in them for creating a vacuum into
which the exhaust steam passes so as to increase the efficiency of
the engine above what it would be if the exhaust steam were obliged
to discharge into the comparatively high pressure of the atmosphere.

     The force of this will be apparent by considering that the
   water consumption of the engine ordinarily is from 15 to 25 lbs.
   of "feed water" per horse power per hour, and the amount of
   "circulating water" required to maintain the vacuum is about 25 to
   30 times the feed water, and in the case of turbines with their 28
   or 29 inch vacuum, much more. For instance, a 1,000 horse power
   plant running on 15 lbs. of feed water and 30 to 1 circulating
   water would require (1,000 × 15) × (30 + 1) = 465,000 lbs. or
   55,822 gals. per hour at full capacity.

=Ques. Besides price what other considerations are important with
respect to water?=

Ans. Its quality and the possibility of a scarcity of supply.

It is quite necessary that the water used in the boilers should be
as free as possible from impurities, so as to prevent the deposition
within them of any scale or sediments. The quality of the water used
for condensing purposes, however, is not quite so important, although
the purer it is the better.

If the plant is to be located in a city, the matter of water supply
need not generally be considered, because, as a rule, it can be
obtained from the waterworks; there will then, of course, be a water
tax to consider and this, if large, may warrant an effort being
made to obtain the water in some other way. In any event, however,
the possibility of a scarcity in the supply should be reduced to a
minimum.

If the plant be located in the country, some natural source of water
would be utilized unless the place be supplied with waterworks, which
is not generally the case. It is usual, however, to find a stream,
lake or pond in the vicinity, but if none such be conveniently near,
an artesian or other form of well must be sunk.

If abundance of water exist in the vicinity of the proposed
installation, not only would the location of the plant be governed
thereby, but the kind of power to be used for its operation would
depend thereon. Thus, if the quantity of the water were sufficient
throughout the entire year to supply the necessary power, water
wheels might be installed and used in place of boilers and steam
engines for driving the generators. The station would then, of
course, be situated close to the waterfall, regardless of the center
of gravity of the system.

[Illustration: FIG. 2,712.--View illustrating the location of a
station as governed by the presence of a water falls. In such cases
the natural water power may be at a considerable distance from the
center of gravity of the distribution system because of the saving
in generation. In the case of long distance transmission very
high pressure may be used and a transformer step down sub-station
be located at or near the center of gravity of the system, thus
considerably reducing the cost of copper for the transmission line.]

=Ques. What should be noted with respect to the coal supply?=

Ans. The facility for transporting the coal from the supply point to
the boiler room.

     In this connection, an admirable location, other conditions
   permitting, is adjacent to a railway line or water front so that
   coal delivered by car or boat may be unloaded directly into the
   bins supplying the boilers.

     If the coal be brought by train, a side or branch track will
   usually be found convenient, and this will usually render any
   carting of the fuel entirely unnecessary.

     In whatever way the coal is to be supplied, the liability of a
   shortage due to traffic or navigation being closed at any time of
   the year should be well looked into, as should also the facility
   for the removal of ashes, before deciding upon the final location
   for the plant.

[Illustration: FIG. 2,713.--View of a station admirably located with
respect to transportation of the coal supply. As shown, the coal may
be obtained either by boat or rail, and with modern machinery for
conveying the coal to the interior of the station, the transportation
cost is reduced to a minimum.]

[Illustration: FIG. 2,714.--Floor plan of part of the turbine central
station erected by the Boston Edison Co., showing two 5,000 kw.
Curtis steam turbines in place. The complete installation contains
twelve 5,000 kw. Curtis steam turbines, a sectional elevation being
shown in fig. 2,758, page 1,971.]

=Choice of System.=--The chief considerations in the design of a
central station are economy and capacity. When the current has to be
transmitted long distances for either lighting or power purposes,
economy is attainable only by reducing the weight of the copper
conductors. This can be accomplished only by the use of the high
voltage currents obtainable from alternators.

Again, where the consumers are located within a radius of two miles
from the central station, thereby requiring a transmission voltage of
550 volts or less, dynamos may be employed with greater economy.

Alternating current possesses serious disadvantages for certain
important applications.

For instance, in operating electric railways and for lighting it is
often necessary to transmit direct current at 500 volts a distance
of five or ten miles. In such cases, the excessive drop cannot be
economically reduced by increasing the sizes of the line wire, while
a sufficient increase of the voltage would cause serious variations
under changes of load. Hence, it is common practice to employ some
form of auxiliary generator or booster, which when connected in
series with the feeder, automatically maintains the required pressure
in the most remote districts so long as the main generators continue
to furnish the normal or working voltage.

The advantage of a direct current installation in such cases over a
similar plant supplying alternating current line is the fact that a
storage battery may be used in connection with the former for taking
up the fluctuations of the current, thereby permitting the dynamo to
run with a less variable load, and consequently at higher efficiency.

=Ques. Name some services requiring direct current.=

Ans. Direct current is required for certain kinds of electrolytic
work, such as electro-plating, the electrical separation of
metals, etc., also the charging of storage batteries for electric
automobiles.

[Illustration: FIG. 2,715.--Example of central station located
remote from the distributing center and furnishing alternating
current at high pressure to a sub-station where the current is passed
through step down transformers and supplied at moderate pressure
to the distribution system. In some cases the sub-station contains
also converters supplying direct current for battery charging,
electro-plating, etc.]

=Ques. How is direct current supplied?=

Ans. Sometimes the central station is equipped with suitable
apparatus for supplying both direct and alternating current. This may
be accomplished in several different ways: By installing both direct
and alternating current generators in the central station; by the use
of double current generators or dynamotors, from which direct current
may be taken from one side and alternating current from the other
side; or by installing, in the sub-station of an alternating current
central station, in addition to the transformers usually placed
therein, a rotary converter for changing or converting alternating
current into direct current.

     Thus, it is evident that the character of a central station
   will be governed to a great extent by the class of services to be
   supplied.

     An exception to this is where the entire output has to be
   transmitted a long distance to the point of utilization.

     In such cases a copper economy demands the use of high tension
   alternating current, and its distribution to consumers may be made
   directly by means of step down transformers mounted near by or
   within the consumers' premises, or it may be transformed into low
   voltage alternating current by a conveniently located sub-station.

     Where the current is to be used chiefly for lighting and there
   are only a few or no motors to be supplied, the choice between
   direct current and alternating current will depend greatly upon
   the size of the installation, direct current being preferable
   for small installations and alternating current for large
   installations.

     If the current is to be used primarily for operating machinery,
   such as elevators, travelling cranes, machine tools and other
   devices of a similar character, which have to be operated
   intermittently and at varying speeds and loads, direct current is
   the more suitable; but if the motors performing such work can be
   operated continuously for many hours at a time under practically
   constant loads, as, for instance in the general work of a pumping
   station, alternating current may be employed with advantage.

[Illustration: FIG. 2,716.--Diagram illustrating diversity factor.
By definition _diversity factor = combined actual maximum demand of
a group of customers divided by the sum of their individual maximum
demands_. Example, a customer has fifty (50) watt lamps and, of
course, the sum of the individual maximum demands of the lamps is 2.5
kw. watts ("connected load"). The customer's maximum demand, however,
is 1.5 kw. Hence, the diversity factor[A] of the customer's group of
lamps is 1.5 ÷ 2.5 = .6. In the diagram the ordinates of the curves
show the ratio _maximum demand_ to _connected load_ for various kinds
of electric lighting service in Chicago.]

[A] NOTE.--The diversity factor of a customer's group of lamps,
namely, the ratio of maximum demand to connected load is usually
called the _demand factor_ of the customer.

=Size of Plant.=--Before any definite calculation can be made, or
plans drawn, the engineer must determine the probable load. This is
usually ascertained in terms of the number and distances of lamps
that will be required, by making a thorough canvass of the city or
town, or that portion for which electrical energy is to be supplied.
The probable load that the station is to carry when it begins
operation, the nature of this load, and the probable rate of increase
are matters upon which the design and construction chiefly depend.

[Illustration: FIG. 2,717.--Load curve for one day.]

=Ques. What is the nature of the load carried by a central station?=

Ans. It fluctuates with the time of day and also with the time of
year.

=Ques. How is a fluctuating load best represented?=

Ans. Graphically, that is to say by means of a curve plotted on
coordinate paper of which ordinates represent load values and the
corresponding abscissæ time values, as in the accompanying curves.

=What is the nature of a power load?=

Ans. Where electricity is supplied for power purposes to a number of
factories, the load is fairly steady, dropping, of course, during
meal hours. In the case of traction, the average value of the load is
fairly steady but there are momentarily violent fluctuations due to
starting cars or trains.

[Illustration: FIG. 2,718.--Load curve for one year.]

=Ques. What is the peak load?=

Ans. The maximum load which has to be carried by the station at any
time of day or night as shown by the highest point of the load curve.

=Ques. Define the load factor.=

Ans. The machinery of the station evidently must be large enough to
carry the peak load, and therefore considerably in excess of that
required for the average demand. The ratio of the average to the
maximum load is called the load factor.

     There are two kinds of load factor: the annual, and the daily.

     The annual load factor is obtained as a percentage by
   multiplying the number of units sold (per year) by 100, and
   dividing by the product of the maximum load and the number of
   hours in the year. The daily load factor is obtained by taking the
   figures for 24 hours instead of a year.

[Illustration: FIG. 2,719.--Load curve of plant supplying power for
the operation of motors in a manufacturing district. The horizontal
dotted lines show suitable power ratings. A properly designed steam
plant has a large overload capacity, a hydraulic plant has a small
overload capacity, and a gasoline engine plant has no overload
capacity. Accordingly, the peak of the load (maximum load) may be 25
or 30 per cent. in excess of the rated capacity of a steam plant,
not more than 5 or 10 per cent. in excess of the rated capacity of a
hydraulic plant, not at all in excess of the rated capacity of a gas
engine plant.]

=Ques. What must be provided in addition to the machinery required to
supply the peak load?=

Ans. Additional units must be installed for use in case of repairs or
break down of some of the other units.

     EXAMPLE.--What would be the boiler horse power required to
   generate 5,000 kw. under the following conditions: Efficiency of
   generators 85%; efficiency of engines 90%; feed water of engines
   and auxiliaries 15 lbs. per I. H. P.; boiler pressure 175 lbs.;
   temperature of feed water 150° Fahr? With a rate of combustion of
   15 lbs. of coal per sq. foot of grate per hour and an evaporation
   (from and at 212°) of 8 lbs. of water per lb. of coal, what area
   of grate would be required and how much heating surface?

           5,000 kw. = 5,000 ÷ .746 = 6,702= electrical horse power

     To obtain this electrical horse power with alternators whose
   efficiency is 85% requires

           6,702 ÷ .85 = 7,885 brake horse power at the engine

     This, with mechanical efficiency of 90% is equivalent to

           7,885 ÷ .9 = 8,761 indicated horse power

     Since 15 lbs. of feed water are required for the engines and
   auxiliaries per indicated horse power per hour, the total feed
   water or evaporation required to generate 5,000 kw. is

           15 × 8,761 = 131,415 lbs. per hour.

     that is to say, the boilers must be of sufficient capacity
   to generate 131,415 lbs. of steam per hour from water at a
   temperature of 150° Fahr. This must be multiplied by the _factor
   of evaporation_ for steam at 175 lbs. pressure from feed water at
   a temperature of 150°, in order to get the equivalent evaporation
   "_from and at 212_°."

     The formula for the factor of evaporation is

                           H - _h_
           factor of evaporation = -------    (1)
                           965.7

     in which

         H = total heat of steam at the observed pressure;
       _h_ = total heat of feed water of the observed temperature;
     965.7 = latent heat, of steam at atmospheric pressure.

     Substituting in (1) values for the observed pressure and
   temperature as obtained from the steam table

                                    1,197 - 118
           factor of evaporation = ------------ = 1.117
                                       965.7

     for which the equivalent evaporation "_from and at 212_°" is

           131,415 × 1.117 = 146,791 lbs.= per hour


                         =FACTORS OF EVAPORATION=

  -------------+-----------------------------------------------------+
   Temp of     |        STEAM PRESSURE BY GAUGE             |
   feed water. +-----+-----+-----+-----+-----+-----+-----+-----+-----+
   Deg. Fahr.  |  50 |  60 |  70 |  80 |  90 | 100 | 110 | 120 | 130 |
  -------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+
        32     |1.214|1.216|1.220|1.222|1.225|1.227|1.229|1.231|1.232|
        40     |1.206|1.209|1.212|1.214|1.216|1.219|1.220|1.222|1.224|
        50     |1.195|1.197|1.201|1.204|1.206|1.208|1.210|1.212|1.214|
        60     |1.185|1.188|1.191|1.193|1.196|1.198|1.200|1.202|1.203|
        70     |1.175|1.178|1.180|1.183|1.185|1.187|1.189|1.191|1.193|
        80     |1.164|1.167|1.170|1.173|1.175|1.177|1.179|1.181|1.183|
        90     |1.154|1.157|1.160|1.162|1.165|1.167|1.169|1.170|1.172|
       100     |1.144|1.147|1.150|1.152|1.154|1.156|1.158|1.160|1.162|
       110     |1.133|1.136|1.139|1.142|1.144|1.146|1.148|1.150|1.152|
       120     |1.123|1.126|1.129|1.131|1.133|1.136|1.138|1.140|1.141|
       130     |1.113|1.116|1.118|1.121|1.123|1.125|1.127|1.129|1.130|
       140     |1.102|1.105|1.108|1.110|1.113|1.115|1.117|1.119|1.120|
       150     |1.091|1.095|1.098|1.100|1.102|1.104|1.106|1.108|1.110|
       160     |1.081|1.084|1.087|1.090|1.092|1.094|1.096|1.098|1.100|
       170     |1.070|1.074|1.077|1.079|1.081|1.083|1.085|1.087|1.089|
       180     |1.060|1.063|1.066|1.069|1.071|1.073|1.075|1.077|1.079|
       190     |1.050|1.053|1.056|1.058|1.060|1.063|1.065|1.066|1.068|
       200     |1.039|1.043|1.045|1.048|1.050|1.052|1.054|1.056|1.058|
       210     |1.029|1.032|1.035|1.037|1.040|1.042|1.044|1.046|1.047|
  -------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+
   Temp of     |        STEAM PRESSURE BY GAUGE             |
   feed water. +-----+-----+-----+-----+-----+-----+-----+-----+-----+
   Deg. Fahr.  | 140 | 150 | 160 | 170 | 180 | 190 | 200 | 210 | 220 |
  -------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+
        32     |1.234|1.236|1.237|1.239|1.240|1.241|1.243|1.244|1.245|
        40     |1.226|1.227|1.229|1.230|1.232|1.233|1.234|1.236|1.237|
        50     |1.215|1.217|1.218|1.220|1.221|1.223|1.224|1.225|1.226|
        60     |1.205|1.207|1.208|1.210|1.211|1.212|1.214|1.215|1.216|
        70     |1.194|1.196|1.197|1.199|1.200|1.202|1.203|1.205|1.206|
        80     |1.184|1.186|1.187|1.189|1.190|1.192|1.193|1.194|1.195|
        90     |1.174|1.176|1.177|1.179|1.180|1.181|1.183|1.184|1.185|
       100     |1.164|1.165|1.167|1.168|1.170|1.171|1.172|1.174|1.175|
       110     |1.153|1.155|1.156|1.158|1.159|1.160|1.162|1.163|1.164|
       120     |1.143|1.145|1.146|1.147|1.149|1.150|1.151|1.153|1.154|
       130     |1.132|1.134|1.136|1.137|1.138|1.140|1.141|1.142|1.144|
       140     |1.122|1.124|1.125|1.127|1.128|1.129|1.131|1.132|1.133|
       150     |1.111|1.113|1.115|1.116|1.118|1.119|1.120|1.121|1.123|
       160     |1.101|1.103|1.104|1.106|1.107|1.108|1.110|1.111|1.112|
       170     |1.091|1.092|1.094|1.095|1.097|1.098|1.099|1.101|1.102|
       180     |1.080|1.082|1.083|1.085|1.086|1.088|1.089|1.090|1.091|
       190     |1.070|1.071|1.073|1.074|1.076|1.077|1.078|1.080|1.081|
       200     |1.059|1.061|1.063|1.064|1.065|1.067|1.068|1.069|1.071|
       210     |1.049|1.051|1.052|1.053|1.055|1.056|1.057|1.059|1.060|
  -------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+
   Temp. of    |        STEAM PRESSURE BY GAUGE             |
   feed water. +-----+-----+-----+-----+-----+-----+-----+-----+-----+
   Deg. Fahr.  | 230 | 240 | 250 | 260 | 270 | 280 | 290 | 300 |     |
  -------------+-----+-----+-----+-----+-----+-----+-----+----+------+
        32     |1.246|1.247|1.248|1.250|1.251|1.252|1.253|1.254|
        40     |1.238|1.239|1.240|1.241|1.242|1.243|1.244|1.245|
        50     |1.228|1.229|1.230|1.231|1.232|1.233|1.234|1.235|
        60     |1.217|1.218|1.219|1.220|1.221|1.222|1.223|1.224|
        70     |1.207|1.208|1.209|1.210|1.211|1.212|1.213|1.214|
        80     |1.196|1.198|1.199|1.200|1.201|1.202|1.203|1.204|
        90     |1.186|1.187|1.188|1.189|1.190|1.191|1.192|1.193|
       100     |1.176|1.177|1.178|1.179|1.180|1.181|1.182|1.183|
       110     |1.166|1.167|1.168|1.169|1.170|1.171|1.172|1.173|
       120     |1.155|1.156|1.157|1.158|1.159|1.160|1.161|1.162|
       130     |1.145|1.146|1.147|1.148|1.149|1.150|1.151|1.152|
       140     |1.134|1.135|1.136|1.137|1.138|1.139|1.140|1.141|
       150     |1.124|1.125|1.126|1.127|1.128|1.129|1.130|1.131|
       160     |1.113|1.115|1.116|1.117|1.118|1.119|1.120|1.121|
       170     |1.103|1.104|1.105|1.106|1.107|1.108|1.109|1.110|
       180     |1.093|1.094|1.095|1.096|1.097|1.098|1.099|1.100|
       190     |1.082|1.083|1.084|1.085|1.086|1.087|1.088|1.089|
       200     |1.072|1.073|1.074|1.075|1.076|1.077|1.078|1.079|
       210     |1.061|1.062|1.063|1.064|1.065|1.066|1.067|1.068|
  -------------+-----+-----+-----+-----+-----+-----+-----+-----+

     One boiler horse power being equal to _an evaporation of_ 34½
   _lbs. of water from a feed water temperature of 212° Fahr., into
   steam at the same temperature_, the boiler capacity is accordingly

           148,105 ÷ 34.5 = 4,293 boiler horse power.

     The rate of evaporation is given at 8 lbs. of water (from and at
   212° Fahr.), for which the fuel required is

           148,105 ÷ 8 = 18,513 lbs. of coal per hour.

     For a rate of combustion of 15 lbs. of coal per hour per square
   foot of grate,

           grate area = 18,513 ÷ 15 = 1,234 sq. ft.

     For stationary boilers the usual ratio of heating surface to
   grate area is 35:1, accordingly the heating surface corresponding
   to this ratio is

           1,234 × 35 = 43,190 sq.ft.

     The above calculation is based on a rate of evaporation of 8
   lbs. of water per lb. of coal and a rate of combustion of 15 lbs.
   of coal per sq. ft. of grate. For other rates the required grate
   area may be obtained from the following table:

  ----------------------------------------------------------------------
                  GRATE SURFACE  PER HORSE  POWER  (KENT)
  ------------+------+-----+--------------------------------------------
              |Pounds|     |
              | of   | Lbs.|  Pounds of coal burned per square foot of
              |water |  of |              grate per hour
              | from | coal+----+----+----+----+----+----+----+----+----
              |and at| per |    |    |    |    |    |    |    |    |
              | 212° | h.p.|  8 | 10 | 12 | 15 | 20 | 25 | 30 | 35 | 40
              | per  | per |    |    |    |    |    |    |    |    |
              |pound | hour+----+----+----+----+----+----+----+----+----
              | of   |     |      Square feet grate per horse power
              | coal |     |
  ------------+------+-----+----+----+----+----+----+----+----+----+----
   Good coal  | }10  | 3.45| .43|.35 | .28| .23| .17| .14| .11| .10| .09
   and boiler | } 9  | 3.83| .48| .38| .32| .25| .19| .15| .13| .11| .10
              |      |     |    |    |    |    |    |    |    |    |
   Fair coal  |{8.61 | 4.  | .50| .40| .33| .26| .20| .16| .13| .12| .10
   or boiler  |{8    | 4.31| .54| .43| .36| .29| .22| .17| .14| .13| .11
              |{7    | 4.93| .62| .49| .41| .33| .24| .20| .17| .14| .12
              |      |     |    |    |    |    |    |    |    |    |
   Poor coal  |{6.9  | 5.  | .63| .50| .42| .34| .25| .20| .17| .15| .13
   or boiler  |{6    | 5.75| .72| .58| .48| .38| .29| .23| .19| .17| .14
              |{5    | 6.9 | .86| .69| .58| .46| .35| .28| .23| .22| .17
              |      |     |    |    |    |    |    |    |    |    |
   Lignite and|}3.45 |10.  |1.25|1.00| .83| .67| .50| .40| .33| .29| .25
   poor boiler|}     |     |    |    |    |    |    |    |    |    |
  ------------+------+-----+----+----+----+----+----+----+----+----+----

=General Arrangement of Station.=--In designing an electrical
station, it is preferable that whatever rooms or divisions of the
interior space are desired should determine the total outside
dimensions of the plant in the original plans of the building than
that these latter dimensions be fixed and the rooms, etc., be fitted
in afterward.

              =SAVING DUE TO HEATING THE FEED WATER=

 Table showing the percentage of saving for each degree of increase in
         temperature of feed water heated by waste steam.

  ----------------------------------------------------------------------
  Init| Pressure of steam in boiler, lbs. per sq. inch above atmosphere
  temp|-----------------------------------------------------------------
   of |
  feed|  0  |  20 |  40 |  60 |  80 | 100 | 120 | 140 | 160 | 180 | 200
  ----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----
   32°|.0872|.0861|.0855|.0851|.0847|.0844|.0841|.0839|.0837|.0835|.0833
   40 |.0878|.0867|.0861|.0856|.0853|.0850|.0847|.0845|.0843|.0841|.0839
   50 |.0886|.0875|.0868|.0864|.0860|.0857|.0854|.0852|.0850|.0848|.0846
   60 |.0894|.0883|.0876|.0872|.0867|.0864|.0862|.0859|.0856|.0855|.0853
   70 |.0902|.0890|.0884|.0879|.0875|.0872|.0869|.0867|.0864|.0862|.0860
   80 |.0910|.0898|.0891|.0887|.0883|.0879|.0877|.0874|.0872|.0870|.0868
   90 |.0919|.0907|.0900|.0895|.0888|.0887|.0884|.0883|.0879|.0877|.0875
  100 |.0927|.0915|.0908|.0903|.0899|.0895|.0892|.0890|.0887|.0885|.0883
  110 |.0936|.0923|.0916|.0911|.0907|.0903|.0900|.0898|.0895|.0893|.0891
  120 |.0945|.0932|.0925|.0919|.0915|.0911|.0908|.0906|.0903|.0901|.0899
  130 |.0954|.0941|.0934|.0928|.0924|.0920|.0917|.0914|.0912|.0909|.0907
  140 |.0963|.0950|.0943|.0937|.0932|.0929|.0925|.0923|.0920|.0918|.0916
  150 |.0973|.0959|.0951|.0946|.0941|.0937|.0934|.0931|.0929|.0926|.0924
  160 |.0982|.0968|.0961|.0955|.0950|.0946|.0943|.0940|.0937|.0935|.0933
  170 |.0992|.0978|.0970|.0964|.0959|.0955|.0952|.0949|.0946|.0944|.0941
  180 |.1002|.0988|.0981|.0973|.0969|.0965|.0961|.0958|.0955|.0953|.0951
  190 |.1012|.0998|.0989|.0983|.0978|.0974|.0971|.0968|.0964|.0062|.0960
  200 |.1022|.1008|.0999|.0993|.0988|.0984|.0980|.0977|.0974|.0972|.0969
  210 |.1033|.1018|.1010|.1003|.0998|.0994|.0990|.0987|.0984|.0981|.0979
  220 |  -- |.1029|.1019|.1013|.1008|.1004|.1000|.0997|.0994|.0991|.0989
  230 |  -- |.1039|.1031|.1024|.1018|.1012|.1010|.1007|.1003|.1001|.0999
  240 |  -- |.1050|.1041|.1034|.1029|.1024|.1020|.1017|.1014|.1011|.1009
  250 |  -- |.1062|.1052|.1045|.1040|.1035|.1031|.1027|.1025|.1022|.1019
  ----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----

     NOTE.--An approximate rule for the conditions of ordinary
   practice is a saving of 1 per cent. made by each increase of
   11° in the temperature of the feed water. This corresponds to
   .0909 per cent. per degree. The calculation of saving is made as
   follows: Boiler pressure, 100 lbs. gauge; total heat in steam
   above 32° = 1,185 B.T.U. feed water, original temperature 60°,
   final temperature 209°F. Increase in heat units, 150. Heat units
   above 32° in feed water of original temperature = 28. Heat units
   in steam above that in cold feed water, 1,185-28 = 1,157. Saving
   by the feed water heater = 150 ÷ 1,157 = 12.96 per cent. The
   same result is obtained by the use of the table. Increase in
   temperature 150° × tabular figure .0864 = 12.96 per cent. Let
   total heat of 1 lb. of steam at the boiler pressure = H; total
   heat of 1 lb. of feed water before entering the heater = _h'_, and
   after passing through the heater = _h''_; then the saving made by
   the heater is (_h''_-_h'_) ÷ (H-_h'_).

Under usual conditions the plans of an electrical station are readily
drawn, as they are generally of a simple nature. The engines and
generators will occupy the majority of the space, and these are
usually placed in one large room; in some stations, however, they are
located respectively in two adjacent rooms. The boilers are generally
located in a room apart from the engines and dynamos, and in some
cases a separate building is provided for them; the pumps, etc., must
be installed not far from the boilers, and space must also be allowed
near the boilers for coal and ashes.

[Illustration: FIG. 2,720.--Floor plan of an electrical station
having a belted drive with counter shaft.]

     Fig. 2,720 shows the floor plan of an electrical station, in
   which a countershaft and belted connections are used between
   the engines and generators. Referring first to the plan of the
   building itself, A represents the engine and dynamo room, B
   denotes the boiler room, C the office, D the store room, and E the
   chimney connected with the boilers by means of the uptake _w_.
   Referring next to the apparatus installed, S, S, S, S represents
   a battery of four boilers; these are connected by steam piping
   VV to the two steam engines, M and M, which are belted to the
   countershaft O. Belted to the countershaft are the generators,
   T, T, T, T, the circuits from which are controlled on the
   switchboard, H.

=Ques. What are the objections to the arrangement shown in
fig. 2,720.=?

Ans. The large space required by the belt drive especially in
locations where land is expensive. Another objection is the
frictional loss due to the belt drive with its countershaft, etc.

[Illustration: FIG. 2,721.--Elevation of station having a belted
drive with countershaft, as shown in plan in fig. 2,720.]

=Ques. What are the desirable features of the belt drive?=

Ans. High speed generators may be used, thus reducing the first
cost, and the multiplicity of speeds and flexibility of the system
resulting from the use of a friction clutch.

     Thus in fig. 2,720, each pulley may be mounted on the counter
   shaft O with a friction clutch. A jaw clutch may also be provided
   at Z, thus permitting the shaft O to be divided into two sections.
   It is therefore possible by this arrangement to cause either of
   the engines to drive any one of the generators, or all of them, or
   both of the engines to drive all of the generators simultaneously.

=Ques. Under what condition is the counter shaft belt drive
particularly valuable?=

Ans. In case of a break down of any one of the engines or generators,
and also when it becomes necessary to clean them without interrupting
the service.

[Illustration: FIG. 2,722.--Plan of station arranged for extension.
The space required for a central station depends upon the number and
kind of lights to be supplied, and upon the character and arrangement
of the machinery. In calculating the size of building required, two
things must be carefully considered: first, the building must be
adapted to the plant to be installed in the beginning; and second, it
must be arranged so that enlargement can be made without disarranging
or interfering with the plant already in existence. This is usually
best secured by providing for expansion in one or two definite
directions, the building being made large enough to accommodate
additional units that will be necessary at some future time because
of the growth of the community and consequent increased demand for
electric current.]

=Ques. How may the design in fig. 2,720 be modified for the
installation of a storage battery?=

Ans. If a storage battery be necessary, a partition may be
constructed across the room A, as indicated by the dotted lines, and
the battery installed in the room thus formed.

[Illustration: FIG. 2,723.--Interior of old Riverside station
showing at the right, seven 6,000 horse power alternators driven by
reciprocating engines, and at the left, a number of turbine units
aggregating 90,000 horse power.]

=Ques. Mention a few details in the general arrangement of the
building fig. 2,720.=

Ans. Two doors to the room A may conveniently be provided at K and L,
the former connecting with the boiler room B, and the latter serving
as the main entrance to the station. There is little that need be
added to what has already been stated regarding the boiler room B.
The door at F provides for the entrance of coal and the removal of
ashes, while at P, the pump and heaters may conveniently be located.
In the office C, visitors may be received, the station reports made
out, bulletins issued from time to time, and whatever engineering
problems arise may here be solved on paper by the engineer in
charge of the plant. The store room D will be found convenient for
various supplies, tools and appliances needed in the operation of
the station. These may here be kept under lock and key and the daily
waste and loss resulting from carelessness avoided.

=Ques. What important point should be noted in locating the engines
and boilers?=

Ans. They should be so placed that the piping between them will be as
short and direct as possible.

=Ques. Why?=

Ans. The steam pipe should be short to reduce the loss of heat
between engine and boiler to a minimum, and both short and direct to
avoid undue friction and consequent drop in pressure of the steam in
passing through the pipe to the engine.

     Entirely too little attention is given to this matter on the
   part of designers and it cannot be too strongly emphasized that,
   for economy, the steam pipe between an engine and boiler should
   be as short and direct as possible, having regard of course, for
   proper piping methods.

=Ques. What should be provided for the steam pipe?=

Ans. A heavy covering of approved material should be placed around
the pipe to reduce the loss of heat by radiation. For this purpose
hair felt, mineral wool and asbestos are used.

[Illustration: FIG. 2,724.--View of engine and condenser, showing how
to arrange the piping to secure good vacuum. _Locate the condenser as
near the engine as possible_; =use easy bends= _instead of elbows;
place the pump_ =below= _bottom of condenser so the water will
drain to pump_. At A is a relief valve, for protection in case the
condenser become flooded through failure of the pump, and at B is
a gate valve to shut off condenser in case atmospheric exhaust is
desired to permit repairs to be made to condenser during operation.
=A water seal= should be maintained on the relief valve and =special
attention= _should be given to the stuffing box_ of the gate valve
=to prevent air leakage=. _The discharge valve of the pump should be
water sealed._]

=Ques. How should the piping be arranged between the engine and
condenser, and why?=

Ans. It should be as short and direct as possible; especially should
elbows be avoided so that the back pressure on the engine piston will
be reduced as near as can be to that of the condenser.

     That is to say, in order to get nearly the full effect of the
   vacuum in the condenser the frictional resistance of the piping
   should be reduced to a minimum.

     Where 90° turns are necessary, easy bends should be used instead
   of sharp elbows. The force of this argument must be apparent by
   noting the practice of steam turbine builders of placing the
   turbine right up against the condenser, and remembering that a
   high vacuum is necessary to the economical working of a turbine.
   See fig. 1,445, page 1,182.

=Ques. What are the considerations respecting the number and type of
engine to be used?=

Ans. In the illustration fig. 2,720, two engines M and M' are
employed, one belted to each end of the countershaft O. These engines
should be of similar or identical pattern; for a small output
they may be either simple or compound, as the conditions of fuel
expenditure may dictate, but if the output be large, triple expansion
engines or turbines are advisable.

[Illustration: FIG. 2,725.--"Dry pipe" for horizontal boiler: it is
connected to the main outlet and its upper surface is perforated with
small holes, the far end being closed. With this arrangement steam is
taken from the boiler over a large area, so that it will contain very
little moisture. _All horizontal boilers without a dome should be
fitted with a dry pipe;_ most engineers do not realize the importance
of obtaining dry steam for engine operation.]

     Corliss or similar slow speed engines may advantageously be used
   in either case. In all cases the engine should be run condensing
   unless the cost for circulating water is prohibitive; even in such
   cases cooling towers may be installed and effect a saving.

     In operation, during the greater part of the day, one engine
   running two or perhaps three of the generators, will carry the
   load, but when the load is particularly heavy, as in the morning
   and evening, both engines and all the generators may be required
   to meet the demands.

[Illustration: FIG. 2,726.--Method of connecting a header to a
battery of boilers. Where two or more boilers are connected to a
single header, the use of a reliable non-return boiler stop valve is
necessary, and in some countries their installation is compulsory. A
non-return boiler stop valve will instantly close should the pressure
in the boiler to which it is attached suddenly decrease below that
in the header, and thereby prevent the entrance of steam from the
other boilers of the battery. This sudden decrease in pressure may be
caused by a ruptured fitting or the blowing out of a tube, in which
event an ordinary stop valve taking the place of a non-return boiler
stop valve would be inadequate, as the loss of steam from the other
boilers of the battery would be tremendous before an ordinary valve
could be reached and closed, assuming that it would be possible to do
so, which in the majority of cases it is not. Should it be desired
to cut out a boiler for cleaning or repairs, the non-return boiler
stop valve will not permit steam to enter the boiler from the header,
even should the handwheel be operated for this purpose, as it cannot
be opened by hand, but can, however, be closed. A non-return boiler
stop valve should be attached to each boiler and connected to an
angle valve on the header. A pipe bend should be used for connecting
the valves, as this will allow for expansion and contraction. The
pipe should slope a trifle downward toward the header and a suitable
drain provided. This drain should be opened and all water permitted
to escape before the angle valve is opened, thereby preventing any
damage due to water hammer.]

     By exercising a little ingenuity in shifting the load on
   different machines at different times, both engines and dynamos,
   may readily be cleaned and repaired without interrupting the
   service.

=Ques. For economy what kind of steam should be used?=

Ans. Super-heated steam.

     The saving due to the use of superheated steam is about 1% for
   every ten degrees Fahr. of super-heat. It should be used in all
   cases.

=Ques. How should the machines be located?=

Ans. Sufficient space should be allowed between them that cleaning
and repairing may be done easily, quickly and effectually.

[Illustration: FIGS. 2,727 and 2,728.--Method of preventing vibration
and of supporting pipes. The figures show top and side views of
a main header carried in suitable frames fitted with adjustable
roller. While the pipe is illustrated as resting on the adjustable
rollers, nevertheless the rollers may also be placed at the sides
or on top of the pipe to prevent vibration, or in cases where the
thrust from a horizontal or vertical branch has to be provided for.
This arrangement will take care of the vibration without in any way
preventing the free expansion and contraction of the pipe.]

=Ques. How should the switchboard be located?=

Ans. In fig. 2,720, the switchboard H is mounted against the wall
dividing the room A from the room B, and is in line with the machines.

     The advantages arising from a switchboard thus installed are,
   that the switchboard attendant working thereon can obtain at any
   time an unobstructed view of the performance of each individual
   machine, and he has in consequence a much better control of them;
   then, too, while he is engaged at the engines or generators he
   can also see the measuring instruments on the switchboard, and
   ascertain approximately the readings upon them.

     In cases of emergency it is sometimes necessary for the
   engineer in charge of a plant to be in several places at the same
   time in order to prevent an accident, and that this seemingly
   impossibility may be approximated as nearly as possible, it is
   essential that the controlling devices be located as closely
   together as is consistent, and that no moving belt or pulley
   intervene between them.

     These conditions are well satisfied in fig. 2,720, and owing to
   the short distances between the generators and the switchboard the
   drop of voltage in each of the conducting wires between them will
   be low.

     This latter advantage is worthy of notice in a station
   generating large currents at a low pressure. To offset the
   advantages just mentioned, the location of the switchboard in
   line with the machines introduces an element of danger to the
   switchboard, its apparatus, and the attendant, on account of the
   possible bursting of a flywheel or other parts of the machines
   from centrifugal force.

[Illustration: FIGS. 2,729 and 2,730.--Points on placing stop valves.
The first and most important feature is to ascertain whether the
valve will act as a water trap for condensed steam. Fig. 2,729
illustrates a common error in the placing of valves, as this
arrangement permits of an accumulation of condensed steam above the
valve when closed, and should the engineer be careless and open the
valve suddenly, serious results might follow owing to water-hammer.
Fig. 2,730 illustrates the correct method of placing the valve. It
sometimes occurs, however, that it is not convenient to place the
valve as shown in fig. 2,730 and that fig. 2,729 is the only manner
in which the valve can be placed. In such cases, the valve should
have a drain, and this drain should always be opened before the large
valve is opened.]

     If the switchboard be placed in the dotted position at H', or,
   in fact, at the opposite end of the room A, the damage to life
   and property that might result from the effects of centrifugal
   force would be eliminated, but in place thereof would be the
   disadvantages of an obstructed view of the machines from the
   switchboard, an obstructed view of the switchboard from the
   machines, inaccessibility between these two, and a greater drop
   of voltage in the majority of the conducting wires between the
   generators and the switchboard.

=Ques. Describe a second arrangement of station with belt drive and
compare it with the design shown in fig. 2,720.=

[Illustration: FIG. 2,731.--Plan of electrical station with belt
drive without counter shaft. The installation here represented
consists of two boilers, S, etc., and three sets of engines and
generators, T, M, etc. Sufficient allowance has been made in the
plans, however, for future increase of business, as additional space
has been provided for an extra engine and generator set, as indicated
by the dotted lines.]

Ans. A floor plan somewhat different from that presented in fig.
2,720 is shown in fig. 2,731. Here a belt drive is employed, but no
countershaft is used. Each generator, therefore, is dependent upon
its respective engine, and in consequence the flexibility obtained by
the use of a countershaft is lost. On the other hand, there is less
loss of mechanical power between the engines and generators in the
driving of the latter, and less floor space is necessary in the room
A. If, however, the floor area of this room be made the same as in
the previous arrangement and the same number of machines are to be
installed, they may be spaced further apart, affording in consequence
considerably more room for cleaning and repairing them.

     In operation, the normal conditions should be such that any two
   of the engine and generator sets may readily carry the average
   load, the third set to be used only as a reserve either to aid the
   other two when the load is unusually heavy or to replace one of
   the other sets when it becomes necessary to clean or repair the
   latter.

     The switchboard may perhaps be best located at H, as a similar
   position on the opposite side of the room A would bring it beneath
   one or more of the steam pipes and thus endanger it should a
   possible leakage occur from these pipes. If located at H, however,
   it will be in line with the machines, and therefore will be
   subject to the disadvantages previously mentioned for such cases;
   consequently it might be as well to place it at the further end
   of the room, either against the partition (shown dotted) of the
   storage battery room if this be built, or else (if no storage
   battery is to be installed), against the end wall itself. The
   nearer end of the room A would not be very desirable for the
   switchboard installation on account of being so far removed from
   the machines, and therefore more or less inaccessible from them.
   Outside of what has now been mentioned, the division of the floor
   plan and the arrangement therein is practically the same as in
   fig. 2,720, accordingly what has already been stated regarding the
   former installation applies, therefore, with equal force to the
   present installation.

=Ques. Describe a plant with direct drive.=

Ans. This type of drive is shown in fig. 2,732. Each engine is
directly connected to a generator, that is, the main shafts of both
are joined together in line so that the generator is driven without
the aid of a belt.

=Ques. What is the advantage of direct drive?=

Ans. The great saving in floor space, which is plainly shown in fig.
2,732, the portion A' representing the saving which results over the
installations previously illustrated in figs. 2,720 and 2,731.

=Ques. How could the floor space be further reduced?=

Ans. By employing vertical instead of horizontal engines.

=Ques. What should be done before drawing the plans for the station?=

Ans. The types of the various machines and apparatus to be installed
should, as nearly as possible, be selected in advance so that their
approximate dimensions may serve as a guide in drawing up the plans
of the building.

[Illustration: FIG. 2,732.--Plan of electrical station containing
direct connected units. As shown, space is provided for an extra
boiler and engine and generator set, as indicated by the dotted
lines. Space also exists for a storage battery room if necessary, and
the partition dividing this room from the engine and dynamo room is
shown by a dotted line as in previous cases.]

     Owing to the great difference in these dimensions for the
   various types, and in fact for the same types as manufactured by
   different concerns, no definite rules regarding the necessary
   space required can here be given. In a general way, however, the
   author has endeavoured to indicate by the drawings the relative
   amounts of space that ordinarily would be considered sufficient.

=Ques. What is the disadvantage of direct drive?=

Ans. A more expensive generator is required because it must run at
the same speed as the engine, which is relatively low as compared
with that of a belted generator.

=Station Construction.=--The construction or rearrangement of the
building intended for the plant is a problem that under ordinary
conditions would be solved by an architect, or at least by an
architect with the assistance of an electrical or mechanical
engineer, still there are many installations where the electrical
engineer has been compelled to design the building.

In such instances he should be equipped with a general knowledge of
the construction of buildings.

=Foundations.=--The foundation may be either natural or artificial;
that is, it may be composed of rock or soil sufficiently solid
to serve the purpose unaided, or it may be such as to require
strengthening by means of wood or iron beams, etc. In either case any
tendency toward a considerable settling or shifting of the foundation
due to the action of water, frost, etc., after the station has been
completed must be well guarded against. To this end special attention
should be given to the matter of drainage.

=Ques. How should the foundation be constructed for the machines?=

Ans. The foundations constructed for the machines should be entirely
separate from that built for the walls of the building, so that the
vibrations of the former will not affect the latter.

     If there be several engines and dynamos to be installed, it is
   best to construct two foundations, one for the engines and one for
   the dynamos. If, however, there be considerable distance between
   the units, it may be advisable to build a separate foundation
   for each engine and for each dynamo. The material of which these
   foundations are composed should if the machines be of 20 horse
   power or over, possess considerable strength and be impervious to
   moisture. Brick, stone and concrete are desirable for the purpose,
   and only the best quality of cement mortar should be employed.
   Care must be taken that lime mortar is not used in place of
   cement mortar, as the former is not well adapted to withstand the
   vibrations of the machines without crumbling.

[Illustration: FIG. 2,733.--Angle for foundation footing. In ordinary
practice the footing courses upon which the walls of the building
proper rest, consist of blocks or slabs of stone as large as are
available and convenient to handle. Footings of brick or concrete are
also used in very soft soils; footings consisting of timber grillage
are often employed. A grillage of iron or steel beams has also
been used successfully. The inclination of the angle φ, of footing
should be about as follows: for metal footings 75°; for stone, 60°;
for concrete, 45°; for brick, 30°. Damp proof courses of slate, or
layer of asphalt are laid in or on the foundations or lower walls to
prevent moisture arising or penetrating by capillary attraction.]

=Ques. Describe a method of constructing foundations.=

Ans. An excavation is made to the desired depth and a form inserted
corresponding to the desired dimensions for the foundation. A
template is placed on top locating all the centers, with iron
pipes suspended from these centers, two or three sizes larger than
the anchor bolts. At the lower end of the pipes are core boxes.
Concrete is poured into the mould thus formed, and when hard, the
forms are removed thus leaving the solid foundation. The anchor
bolts are inserted through the pipes and passed through iron plates
at the lower end as shown in fig. 2,734, being secured by nuts. By
using pipe of two or three bolt diameters a margin is provided for
adjustment so the bolts will pass through the holes in the frame of
the machine thus allowing for any slight errors in laying out the
centers on the template.

[Illustration: FIG. 2,734.--Concrete foundation showing method of
installing the anchor bolts.]

=Ques. What is the object of the openings in the bottom of the
foundation?=

Ans. In case of a defective bolt, it may be replaced by a new one
without injury to the foundation.

=Walls.=--Regarding the material for the walls of the station iron,
stone, brick and wood may be considered. Of these, iron in the form
of sheets or plates would be entirely fireproof, but being itself
a conductor would introduce difficulties in maintaining a high
insulation resistance of the current carrying circuits; it would
also make the building difficult to heat in winter and to keep cool
in summer. Stone in the form of limestone, granite or sandstone, as
a building material is desirable for solidity and attractiveness;
it is also fireproof and an insulator, but the high cost of such a
structure for an electrical station usually prohibits its use except
in private plants or in electrical stations located in large cities.

[Illustration: FIG. 2,735.--View showing part of template for
locating anchor bolt centers, pipes through which the bolts pass
and bolt boxes at lower end of bolts. The completed foundation is
shown in fig. 2,734, with template removed. The template is made of
plain boards upon which the center lines are drawn, and bolt center
located. Holes are bored at the bolt centers to permit insertion of
the pipes as shown.]

Brick is a good material and is readily obtained in nearly all parts
of the country; it is comparatively cheap, and is also an insulating
and fireproof material. The bricks selected for this purpose should
possess true sharp edges, and be hard burned.

=Ques. What are the features of wood?=

Ans. Wood forms the cheapest material that can be used for the walls
of electrical stations, and it usually affords satisfaction, but has
the disadvantage of high fire risk.

=Roofs=.--In fig. 2,736 is shown one form of construction for the
roof of an electrical station. The end view here presented shows
the upper portion of the walls at B and D; these support the iron
trusses C, and the roof proper MN. In many stations there is provided
throughout the length of the building, a monitor or raised structure
on the peak of the roof for ventilation and light. The end view of
the monitor is shown at S in the figure; its sides should be fitted
with windows adjustable from the floor.

[Illustration: FIG. 2,736.--One form of roof construction.]

=Floors.=--The floor of the station should be so designed that
it will be capable of supporting a reasonable weight, but as the
weights of the machines are borne entirely by their respective
foundations the normal weight upon the floor will not be great; for
short periods, however, it may be called upon to support one or two
machines while they are being placed in position or interchanged,
and due allowance must be made for such occurrences.

Station floors for engine and dynamo rooms are, as a rule,
constructed of wood. Where very high currents are generated, however,
insulated floors of special construction mounted on glass are
necessary as a protection from injurious shocks. Brick, concrete,
cement, and other substances of a similar nature are objectionable
as a floor material for engine and dynamo rooms on account of the
grit from them, caused by constant wear, being liable to get into the
bearings of the machines.

Where there are no moving parts, however, as in the boiler room, the
materials just mentioned possess no disadvantages and are preferable
to wood on account of being fireproof.

           =THEORETICAL DRAFT PRESSURE IN INCHES OF WATER IN=
                    =A CHIMNEY 100 FEET HIGH=

       (For other heights the draft varies directly as the height)

   Temp. in       TEMP. OF EXTERNAL AIR. (BAROMETER 30 INCHES)
  Chimney, °F.   0°  10°  20°  30°  40°  50°  60°  70°  80°  90° 100°
      200°     .453 .419 .384 .353 .321 .292 .263 .234 .209 .182 .157
      220      .488 .453 .419 .388 .355 .326 .298 .269 .244 .217 .192
      240      .520 .488 .451 .421 .388 .359 .330 .301 .276 .250 .225
      260      .555 .528 .484 .453 .420 .392 .363 .334 .309 .282 .257
      280      .584 .549 .515 .482 .451 .422 .394 .365 .340 .313 .288
      300      .611 .576 .541 .511 .478 .449 .420 .392 .367 .340 .315
      320      .637 .603 .568 .538 .505 .476 .447 .419 .394 .367 .342
      340      .662 .638 .593 .563 .530 .501 .472 .443 .419 .392 .367
      360      .687 .653 .618 .588 .555 .526 .497 .468 .444 .417 .392
      380      .710 .676 .641 .611 .578 .549 .520 .492 .467 .440 .415
      400      .732 .697 .662 .632 .598 .570 .541 .513 .488 .461 .436
      420      .753 .718 .684 .653 .620 .591 .563 .534 .509 .482 .457
      440      .774 .739 .705 .674 .641 .612 .584 .555 .530 .503 .478
      460      .793 .758 .724 .694 .660 .632 .603 .574 .549 .522 .497
      480      .810 .776 .741 .710 .678 .649 .620 .591 .566 .540 .515
      500      .829 .791 .760 .730 .697 .669 .639 .610 .586 .559 .534

=Chimneys.=--These are generally constructed of brick and iron,
sometimes of concrete. Iron chimneys cost less than brick chimneys,
necessitate less substantial foundations, and are free from the
liability of cracking. They must be painted to prevent corrosion, are
less substantial, and lose considerably more heat by radiation than
do brick chimneys.

[Illustration: FIG. 2,737.--An example of direct connected unit with
gas engine power. The view shows a Westinghouse 200 kva., 4,000 volt,
three phase, 60 cycle alternator direct connected to a gas engine.]

[Illustration: FIG. 2,738.--Curves showing comparative costs of
chimney and mechanical draft. In certain of these, the cost of the
existing chimney is known, and that of the complete mechanical draft
plant is estimated, while in others, the cost of mechanical draft
installation is determined from the contract price, and the expense
of a chimney to produce equivalent results is calculated. Costs are
shown for both single, forced and induced engine driven fans and
for duplex engine driven plants, in which either fan may serve as a
relay. An apparatus of the latter type is the most expensive, and
finds its greatest use where economizers are employed.]

Both brick and iron chimneys, require an inner wall or lining of
brick, which forms the flue proper, and in order that this wall be
not cracked by sudden cooling an air space is left between it and
the outer wall. In a brick chimney the inner wall need not extend
much beyond half the height of the chimney, but when iron is used it
should reach to the top.

=Ques. Upon what does the force of natural draught in a chimney
depend?=

Ans. It depends upon the difference between the weight of the column
of hot gases inside the chimney and the weight of a like column of
the cold external air.

[Illustration: FIGS. 2,739 and 2,740.--Substituting mechanical
draught in place of chimney. The relative proportions of a brick
chimney, and of the smoke pipe required when mechanical draft is
introduced are forcibly shown in the illustrations, which show the
works of the B.F. Sturtevant Co., at Jamaica Plain, Mass. The removal
of the boilers to a position too far distant from the existing
chimney to permit of its longer fulfilling its office, led to the
substitution of an induced draft fan and the subsequent removal of
the chimney. The present stack or smoke pipe, barely visible in fig.
2,740, extends only 31 feet above the ground, and no trouble is
experienced from smoke.]

=Ques. How is the intensity of the draught expressed?=

Ans. In terms of the number of inches of a water column sustained by
the pressure produced.

=Ques. Are high chimneys necessary?=

Ans. No.

     _Chimneys above 150 feet in height are very costly, and their
   increased cost is not justified by increased efficiency._

[Illustrations: FIGS. 2,741 to 2,744.--Installation of forced draft
system to old boiler plant. The figures illustrate the simplest
method. The fan which is of steel plate with direct connected double
cylinder engine, is placed immediately over the end of a brick duct
into which the air is discharged. This duct is carried under ground
across the front of the boilers, to the ash pits of each of which
connection is made through branch ducts. Each branch duct opening
is provided with special ash pit damper, operated by notched handle
bar, as illustrated in the detail. This method of introduction
serves to distribute the air within the ash pit, and to secure even
flow through the fuel upon the grate above. Of course, the ash pit
doors must remain closed in order to bring about this result. A
chimney of sufficient height to merely discharge the gases above
objectionable level is all that is absolutely necessary with this
arrangement. Although the introduction of a fan in an old plant is
usually evidence of the insufficiency of the existing chimney to meet
the requirements, such a chimney, will, however, usually serve as a
discharge pipe for the gases when the fan is employed. The fan thus
becomes more than a mere auxiliary to the chimney; it practically
supplants it so far as the method of draught production is concerned.]

     The latest chimney practice is to build two or more small
   chimneys instead of one large one. A notable example is the
   Spreckels Sugar Refinery in Philadelphia, where three separate
   chimneys are used for one boiler plant of 7,500 horse power. The
   three chimneys are said to have cost several thousand dollars less
   than an equivalent single chimney.

     =Very tall chimneys= have been characterized by one writer as
   "_monuments to the folly of their builders._"

[Illustration: FIGS. 2,745 and 2,746.--Comparison of chimney draft
and mechanical draft. The illustrations show a plant of 2,400 H.P. of
modern water tube boilers, 12 in number, set in pairs and equipped
with economizers. Fig. 2,745 indicates the location of a chimney, 9
feet in internal diameter by 180 feet high, designed to furnish the
necessary draft; fig. 2,746 represents the same plant with a complete
duplex induced draught apparatus substituted for the chimney, and
placed above the economizer connections. Each of the two fans is
driven by a special engine, direct connected to the fan shaft, and
each is capable of producing draft for the entire plant. A short
steel plate stack unites the two fan outlets and discharges the gases
just above the boiler house roof. All of the room necessary for the
chimney is saved, and no valuable space is required for the fans.]

=Ques. How is mechanical draft secured?=

Ans. In two ways, known respectively as _induced draught_ and _forced
draught_.

=Ques. Describe the method of induced draft.=

Ans. A fan is located in the smoke flue, and which in operation
draws the gases through the furnace and discharges them into a
_short_ chimney.

=Ques. Describe the method of forced draft.=

Ans. In this method, air is forced into the furnace underneath the
grate bars by means of a fan or a steam jet blower.

[Illustration: FIG. 2,747.--Forced draft plant with hollow bridge
wall at the Crystal Water Co., Buffalo, N. Y. The air is delivered to
the ash pit via the hollow bridge wall, being supplied under pressure
by the blower seen at the side of the boiler setting. As shown, the
blower is operated by a small reciprocating engine; however, compact
blowing units with steam turbine drive can be had and which are
designed to be placed in the boiler setting.]

=Ques. What is the application of the two systems?=

Ans. Induced draft is installed mostly in new plants, while forced
draft is better adapted to old plants.

=Steam Turbines=.--It is not the author's intention to discuss at
length the steam end of the electric plant, because too much space
would be required, and also because the subject belongs properly
to the field of mechanical engineering rather than electrical
engineering. However, because of the recent introduction of the steam
turbine for the direct driving of large generators, and the fact
that it is now almost universally used in large central stations, a
detailed explanation of its principles and construction may not be
out of place.

[Illustration: FIG. 2,748.--Longitudinal section of elementary
Parsons type steam turbine. The turbine consists essentially of a
fixed casing, or cylinder, and a revolving spindle or drum. The ends
of the spindle are extended in the form of a shaft, carried in two
bearings A and B, and, excepting the small parts of the governing
mechanism and the oil pump, these bearings are the only rubbing
parts in the entire turbine. Steam enters from the steam pipe at C
and passes through the main throttle or regulating valve D, which,
as actually constructed, is a balanced valve. This valve is operated
by the governor through suitable controlling mechanism. The steam
enters the cylinder through the passage E and, turning to the left
passes through alternate stationary and revolving rows of blades,
finally emerging from them at F and flowing through the connection
G to the condenser or to the atmosphere, depending upon whether the
turbine is condensing or non-condensing. Each row of blades, both
stationary and revolving, extends completely around the turbine and
the steam flows through the full annulus between the spindle and
the cylinder. In an ideal turbine the lengths of the blades and the
diameter of the spindle which carries them would continuously and
gradually increase from the steam inlet to the exhaust. Practically,
however, the desired effect is produced by making the spindle in
steps, there being generally three such steps or stages, H, J and K.
The blades in each step are arranged in groups of increasing length.
At the beginning of each of the larger steps, the blades are usually
shorter than at the end of the preceding smaller step, the change
being made in such a way that the correct relation of blade length
to spindle diameter is secured. The steam, acting as previously
described, produces a thrust tending to force the spindle toward
the left, as seen in the cut. This thrust, however, is counteracted
by the "balance pistons," L, M and N, which are of the necessary
diameter to neutralize the thrust on the spindle steps, H, J and K,
respectively. These elements are called "pistons" for convenience,
although they do not come in contact with the cylinder, but both
the pistons and the cylinder are provided with alternate rings
which form a labyrinth packing to retard the leakage of steam. In
order that each balance piston may have the proper pressure on both
sides, equalizing passages O, P and Q are provided connecting the
balance pistons with the corresponding stages of the blading. The end
thrust being thus practically neutralized by means of the balance
pistons, the spindle "floats" so that it can be easily moved in one
direction or the other. In order to definitely fix the position of
the spindle, a small adjustable collar bearing is provided at R,
inside the housing of the main bearing B. This collar bearing is
adjustable so as to locate and hold the spindle in such position so
that there will be such a clearance between the rings of the balance
piston and those of the cylinder, that the leakage of steam will be
reduced to a minimum and, at the same time, prevent actual contact
under varying conditions of temperature. Where the shaft passes out
of the cylinder, at S and T, it is necessary to provide against
in-leakage of air or out-leakage of steam by means of glands. These
glands are made tight by water packing without metallic contact. The
shaft of the turbine is extended at U and coupled to the shaft of
the alternator by means of a flexible coupling. The high pressure
turbines are so proportioned that, when using steam as previously
described, they have enough capacity to take care of the ordinary
fluctuations of load when controlled by the governor through the
valve D, thus insuring maximum economy of steam consumption at
approximately the rated load. To provide for overloads, the valve V
is supplied to admit steam to an intermediate stage of the turbine.
This valve shown diagrammatically in the illustration, is arranged
to be operated by the governor and is, according to circumstances,
located either as shown by the illustration, or at another stage of
the turbine.]

[Illustration: FIG. 2,749.--Arrangement of blading in Parsons type
turbine, consisting of alternate moving and stationary blades. The
path taken by the steam is indicated by the arrows.]

A turbine is a machine in which a rotary motion is obtained by
transference of the _momentum_ of a fluid or gas. In general the
fluid is guided by fixed blades, attached to a casing, and, impinging
on other blades mounted on a drum or shaft, causing the latter to
revolve.

Turbines are classed in various ways as: 1, _radial flow_, when the
steam enters near the center and escapes toward the circumference;
and 2, _parallel flow_, when the steam travels _axially_ or parallel
to the length of the turning body.

Turbines are commonly, yet erroneously classed as:

  1. Impulse;
  2. Reaction.

=Ques. What is the distinction between these two types?=

Ans. In the so called impulse type, _steam enters and leaves the
passages between the vanes at the same pressure_. In the so called
reaction type, _the pressure is less on the exit side of the vanes
than on the entrance side_.

     Fig. 2,750 is a sectional view of the Parsons-Westinghouse
   parallel flow turbine. Steam from the boiler enters first a
   receiver in which are the governor controlled admission valves.
   These valves are actuated by a centrifugal governor.

[Illustration: FIG. 2,750.--Sectional view of Parsons-Westinghouse
turbine, showing rotor and governor.]

     _Steam does not enter the turbine in a continuous blast, but
   intermittently, or in puffs._ The speed regulation is therefore
   accomplished by proportioning the duration of these puffs to the
   load of the engine, this being effected by the governor, fig.
   2,752.

     The governor of the turbine has only to move a small pilot
   valve, or slide, E, which admits steam under the piston F, and
   lifts the throttle valve proper off its seat.

     As soon as the pilot valve closes, the spring shifts the main
   throttle valve. Thus, at light loads, the main throttle or
   admission valve is continually opening and shutting at uniform
   intervals, the length of time during which it remains open
   depending upon the load.

     As the load increases, the duration of the valve opening also
   increases, until at full load the valve does not reach its seat at
   all and the steam flows steadily through the turbine. The steam
   thus admitted flows into the annular passage A, fig. 2,750, by the
   opening S, and then past the blades, revolving the rotor.

     When the load increases above the normal rated amount a
   secondary pilot valve is moved by the same means, this in turn
   admitting steam to a piston, similar to F, which lifts another
   throttle valve. This admits steam into the annular space I, so
   that it acts upon the larger diameter of the drum or rotor, giving
   largely increased power for the time being.

     The levers or arms of the governor are mounted upon knife edges
   instead of pins, making it extremely sensitive. The tension spring
   may be adjusted by hand while the turbine is running.

[Illustration: FIG. 2,751.--Sectional view of a combination impulse
and reaction single flow turbine. This is a modification of the
single flow type, in which the smallest barrel of reaction blading is
replaced by an impulse wheel. Steam is admitted to the nozzle block
A, is expanded in the nozzles and discharged against a portion of the
periphery of the impulse wheel. The intermediate and low pressure
stages are identical with the corresponding stages in the single flow
type. The substitution of the impulse element for the high pressure
section of reaction blading has no influence one way or another on
the efficiency. That is to say the efficiency of an impulse wheel is
about the same at the least efficient section of reaction blading.
This design is attractive, however, in that it shortens the machine
materially, and gives a stiffer design of rotor. The entering steam
is confined in the nozzle chamber until its pressure and temperature
have been materially reduced by expanding through the nozzles.
As the nozzle chamber is cast separately from the main cylinder,
the temperature and pressure differences to which the cylinder is
subjected are correspondingly lessened. However, probably on account
of its small diameter at the high pressure section, the straight
Parsons type has always shown itself to be adequate for all of the
steam pressures and temperatures encountered in ordinary practice.]

     The governor does not actually move the pilot valve, but shifts
   the point L in fig. 2,752. A reciprocating motion is given to the
   rod I by a small eccentric on the governor shaft; this is driven
   by worm gearing shown near O in fig. 2,750, so that the eccentric
   makes one revolution to about eight of the turbine. Thus, with a
   turbine running 1,200 revolutions, the rod I would be moved up and
   down 150 times per minute. As the points A and H are fixed, the
   motion is conveyed to the small pilot valve E, thus giving 150
   puffs a minute. The governor in shifting the point L brings the
   edge of the pilot valve nearer the port and so cuts off the steam
   earlier.

     The annular diameter or space between the rotor and the stator
   is gradually increased from inlet to exhaust, the blades being
   made longer in each ring. When the mechanical limit is reached,
   the diameter of the rotor is increased as at I and D so as to
   keep the length of blade within bound.

     Balance pistons as at B, C, F are attached to the rotor,
   their office being to oppose end thrust upon those blades in
   corresponding diameter of the rotor. Communication is established
   through the passage V and pipe M between the eduction pipe and the
   back of these pistons, thus increasing the efficiency of their
   balancing and also taking care of any leakage past them.

     A small thrust bearing T prevents end play of the rotor, and is
   adjustable to maintain the proper clearance between the rings of
   blades; this varies from ⅛ inch at the admission to 1 inch at the
   exhaust. This bearing also takes up any extra unbalanced thrust. A
   turbine should operate with a high vacuum, because without this it
   does not compare favorably with an ordinary reciprocating engine
   from the point of economy.

[Illustration: FIG. 2,752.--Sectional view of governor of the
Parsons-Westinghouse turbine.]

     _Separate air pumps are provided to create the vacuum._

     Where the ordinary type of vertical air pump is employed, a
   booster or _vacuum increaser_ is added, as nothing below 26 inches
   is advisable, 28 and 29 inches being always striven for. It is
   also preferable to use a certain amount of _super-heat_ with steam
   turbines.

     To assist in producing the high vacuum, exhaust passages are
   made large, the eduction passage E in fig. 2,750 being nearly
   twenty-three times the area of the steam pipe.

     Among other details, a noteworthy feature is a small oil pump K,
   which circulates oil through bearings of the machinery, the oil
   being drawn from the tank under the governor shaft and gravitating
   there after use. No pressure of oil is employed. Stuffing rings
   prevent leakage; these consist of alternate grooves and collars in
   shaft and bearing, like the grooves in an indicator piston.

=Ques. Why is a high vacuum desirable?=

Ans. Because the turbine is capable of expanding the steam to a very
low terminal pressure, and this is necessary for economy.

=Ques. What may be said of the working pressures for turbines?=

Ans. To meet the varied conditions of service, turbines are designed
to operate with: 1, high pressure, 2, low pressure, or 3, mixed
pressure.

[Illustration: FIG. 2,753.--Sectional view of a double flow turbine.
The maximum economical capacity of a single flow turbine is limited
by the rotative speed. The economical velocity at which the steam may
pass through the blades of the turbine depends on the velocity of
the moving blades. The capacity of the turbine depends on the weight
of the steam passed per unit of time, which in turn depends on the
mean velocity and the height of the blades. For a given rotative
speed, the mean diameter of blade ring practicable is limited by
the allowable stresses due to centrifugal force, and there is a
practical limit for the height of the blades. Now if the rotative
speed be taken only half as great, the maximum diameter of the rotor
may be doubled and, without increasing the height of the blades, the
capacity of the turbine will be doubled. So with the single flow
steam turbine as well as with the single crank reciprocating engine,
there is a practical limiting economical capacity for any given
speed. If this limit be reached with a single crank reciprocating
engine, a unit of double the power may be produced at the same speed
by coupling two single crank engines to one shaft. Similar results
are secured making a double flow turbine which is in effect, as will
be seen from the figure, two single flow turbines made up in a single
rotor in a single casing with a common inlet and two exhausts. Steam
enters the nozzle block, acts on the impulse element, and then the
current divides, one-half of the steam going through the reaction
blading at the left of the impulse wheel; the remainder passes over
the top of the impulse wheel and through the impulse blading at the
right.]

     High pressure turbines operate at about the same initial
   pressure as triple expansion engines.

     Low pressure, as here applied, means the exhaust pressure of the
   reciprocating engine from which the exhaust steam passes through
   the turbine before entering the condenser.

     Mixed pressure implies that the exhaust steam is supplemented,
   for heavy loads, by the admission of live steam.

=Ques. What determines the working pressure?=

Ans. When all the power is furnished by the turbine, it is designed
for high pressure; when operated in combination with a reciprocating
engine, low pressure is used for constant load, and mixed pressure
for variable load.

[Illustration: FIG. 2,754.--Sectional view of a semi-double flow
turbine. This is a modification in which the intermediate section
of reaction blading is single flow, and the low pressure section
only is double flow. This would be analogous to a four cylinder
triple expansion engine, that is, one with one high pressure, one
intermediate pressure and two low pressure cylinders--a design not at
all uncommon in very large engines in which the required dimensions
of a single low pressure cylinder would be prohibitive. Such turbines
are useful for capacities greater than is desirable for a single
flow turbine, and which are still below the maximum possibilities of
a double flow turbine of the same speed. In such machines the best
efficiency is secured by making the intermediate blading in a single
section large enough to pass the entire quantity of steam. A "dummy"
similar to those used on the single flow Parsons type, shown at the
right of the impulse wheel, compels all of the steam to pass through
the single intermediate section of the reaction blading, and balances
the end thrust due to this section. When the steam issues from the
intermediate section, the current is divided, one-half passing
directly to the adjacent low pressure section, while the other half
passes through the holes shown in the periphery of the hollow rotor
and through the rotor itself, beyond the dummy ring, into the other
low pressure section at the left hand end of the turbine.]

     NOTE.--There are logical engineering reasons for the existence
   of the several types of turbine, viz., single flow, double flow,
   and semi-double flow. The double flow turbine is not inherently
   superior to the single flow design, but is used under conditions
   for which the single flow machine is unsuitable. Similarly, the
   semi-double flow is recommended only for conditions which it can
   meet more satisfactorily than either of the other types.

     NOTE.--Low pressure turbines use exhaust steam from
   non-condensing engines and are valuable as an adjunct to existing
   plants for the purpose of increasing economy and capacity with a
   minimum outlay for new equipment.

     NOTE.--Bleeder turbines are for use in plants which are required
   to furnish, not only power, but also considerable and varying
   quantities of low pressure steam for heating purposes. In these
   turbines a part of the steam after it has done work in the high
   pressure stages may be diverted to the heating system, and the
   remainder expanded through the low pressure blading and exhausted
   into the condenser. In this way none of the energy of the heating
   steam, due to the difference of pressure between the boiler and
   the heating system is wasted. On the other hand if no steam is
   required for heating purposes, the turbine operates just as
   efficiently as though the bleeder feature were absent.

[Illustration: FIG. 2,755.--Westinghouse valve gear with steam relay.
In the smaller turbines, the governor acts directly on the steam
admission valves, opening first the primary valve, and then, if
necessary, the secondary valve, after the primary is fully open. In
turbines of the single flow Parsons type, the governor actuates two
small valves controlling ports leading to steam relay cylinders which
operate the admission valves. The little valve controlling the relay
cylinder for the secondary valve has more lap than the other and
consequently does not come into action until the primary valve has
attained its maximum effective opening. The figure shows the general
design of this type of valve gear.]

     _The De Laval steam turbine_ is termed by its builders a high
   speed rotary steam engine. It has but a single wheel, fitted with
   vanes or buckets of such curvature as has been found to be best
   adapted for receiving the impulse of the steam jet. There are no
   stationary or guide blades, the angular position of the nozzles
   giving direction to the jet. The nozzles are placed at an angle
   of 20 degrees to the plane of motion of the buckets. The best
   energy in the steam is practically devoted to the production of
   velocity in the expanding or divergent nozzle, and the velocity
   thus attained by the issuing jet of steam is about 4,000 feet per
   second. To attain the maximum efficiency, the buckets attached to
   the periphery of the wheel against which this jet impinges should
   have a speed of about 1,900 feet per second, but, owing to the
   difficulty of producing a material for the wheel strong enough to
   withstand the strains induced by such a high speed, it has been
   found necessary to limit the peripheral speed to 1,200 or 1,300
   feet per second.

     It is well known that in a correctly designed nozzle the
   adiabatic expansion of the steam from maximum to minimum pressure
   will convert the entire static energy of the steam into kinetic
   energy. Theoretically this is what occurs in the De Laval nozzle.
   The expanding steam acquires great velocity, and the energy
   of the jet of steam issuing from the nozzle is equal to the
   amount of energy that would be developed if an equal volume of
   steam were allowed to adiabatically expand behind the piston
   of a reciprocating engine, a condition, however, which for
   obvious reasons has never yet been attained in practice with the
   reciprocating engine. But with the divergent nozzle the conditions
   are different.

     _The Curtis turbine_ is built by the General Electric Company at
   their works in Schenectady, N. Y., and Lynn, Mass. They are of the
   horizontal and vertical types. In the vertical type the revolving
   parts are set upon a vertical shaft, the diameter of the shaft
   corresponding to the size of the machine.

     The shaft is supported by and runs upon a step bearing at the
   bottom. This step bearing consists of two cylindrical cast iron
   plates bearing upon each other and having a central recess between
   them into which lubricating oil is forced under pressure by a
   steam or electrically driven pump, the oil passing up from beneath.

[Illustration: FIGS. 2,756 and 2,757.--Westinghouse valve gear with
oil relay. Governors for the larger turbines, particularly those of
the combination impulse and reaction double, or single double flow
type, employ an oil relay mechanism, as shown in the figure, for
operating the steam valves. In these turbines the lubricating oil
circulating pump, maintains a higher pressure than is required for
the lubricating system. The governor controls a small relay valve
A which admits pressure oil to, or exhausts it from the operating
cylinder. When oil is admitted to the operating cylinder raising the
piston, the lever C lifts the primary valve E. The lever D moves
simultaneously with C, but on account of the slotted connection
with the stem of the secondary valve F, the latter does not begin
to lift until the primary valve is raised to the point at which its
effective opening ceases to be increased by further upward travel.
In the Westinghouse designs, the operating valve, A is connected not
only to the governor, but also to a vibrator, which gives it a slight
but continuous reciprocating motion, while the governor controls its
mean position. The effect of this is manifested in a slight pulsation
throughout the entire relay system, which, so to speak, keeps it
"alive" and ready to respond instantly, to the smallest change in
the position of the governor. The oil relay can be made sufficiently
powerful to operate valves of any size, and it is also in effect
a safety device in that any failure of the lubricating oil supply
will automatically and immediately shut off the steam and stop the
turbine.]

     A weighted accumulator is sometimes installed in connection with
   the oil pipe as a convenient device for governing the step bearing
   pumps, and also as a safety device in case the pumps should fail,
   but it is seldom required for the latter purpose, as the step
   bearing pumps have proven after a long service in a number of
   cases, to be reliable. The vertical shaft is also held in place
   and kept steady by three sleeve bearings one just above the step,
   one between the turbine and generator, and the other near the top.

[Illustration: FIG. 2,758.--Elevation of new turbine central station
erected by the Boston Edison Co. The turbine room is 68 feet, 4
inches wide and 650 feet long from outside to outside of the walls.
The boiler room is 149 feet, 6 inches by 640 feet and equipped with
twelve groups of boiler, one group consisting of eight 512 H.P.
boilers for each turbine. The switching arrangements are located in
a separate building as shown in the elevation. The total floor space
covered by boiler room, turbine room and switchboard room is 2.64
square feet per kw. The boilers are all on the ground floor. See fig.
2,714 for plan.]

     These guide bearings are lubricated by a standard gravity feed
   system. It is apparent that the amount of friction in the machine
   is very small, and as there is no end thrust caused by the action
   of the steam, the relation between the revolving and stationary
   blades may be maintained accurately. As a consequence, therefore,
   the clearances are reduced to the minimum.

     The Curtis turbine is divided into two or more stages, and each
   stage has one, two or more sets of revolving blades bolted upon
   the peripheries of wheels keyed to the shaft. There are also the
   corresponding sets of stationary blades bolted to the inner walls
   of the cylinder or casing.

     The governing of speed is accomplished in the first set of
   nozzles and the control of the admission valves here is effected
   by means of a centrifugal governor attached to the top end of the
   shaft. This governor, by a very slight movement, imparts motion
   to levers, which in turn work the valve mechanism.

     The admission of steam to the nozzles is controlled by piston
   valves which are actuated by steam from small pilot valves which
   are in turn under the control of the governor.

[Illustration: FIG. 2,759.--Illustration of a weir. To make a weir,
place a board across the stream at some point which will allow a
pond to form above. The board should have a notch cut in it with
both side edges and the bottom sharply beveled toward the intake,
as shown in the above cut. The bottom of the notch, which is called
the "crest" of the weir, should be perfectly level and the sides
vertical. In the pond back of the weir, at a distance not less than
the length of the notch, drive a stake near the bank, with its top
precisely level with the crest. By means of a rule, or a graduated
stake as shown, measure the depth of water over the top of stake,
making allowance for capillary attraction of the water against the
sides of the weir. For extreme accuracy this depth may be measured
to thousandths of a foot by means of a "hook gauge," familiar to all
engineers. Having ascertained the depth of water over the stake,
refer to the accompanying table, from which may be calculated the
amount of water flowing over the weir. There are certain proportions
which must be observed in the dimensions of this notch. Its length,
or width, should be between four and eight times the depth of water
flowing over the crest of the weir. The pond back of the weir should
be at least fifty per cent. wider than the notch and of sufficient
width and depth that the velocity of flow or approach be not over one
foot per second. In order to obtain these results it is advisable to
experiment to some extent.]

     Speed regulation is effected by varying the number of nozzles
   in flow, that is, for light loads fewer nozzles are open and a
   smaller volume of steam is admitted to the turbine wheel, but the
   steam that is admitted impinges against the moving blades with the
   same velocity always, no matter whether the volume be large or
   small. With a full load and all the nozzle sections in flow, the
   steam passes to the wheel in a broad belt and steady flow.

                           WEIR TABLE
    giving cubic feet of water per minute that will flow over a weir
             one inch wide and from ⅛ to 20⅞ inches deep.

  --------+------+------+------+------+------+------+------+------
   Depth  |      |      |      |      |      |      |      |
   inches |      |   ⅛  |   ¼  |   ⅜  |   ½  |   ⅝  |  ¾   |  ⅞
  --------+------+------+------+------+------+------+------+------
     =0=  |  .00 |  .01 |  .05 |  .09 |  .14 |  .19 |  .26 |  .32
     =1=  |  .40 |  .47 |  .55 |  .64 |  .73 |  .82 |  .92 | 1.02
     =2=  | 1.13 | 1.23 | 1.35 | 1.36 | 1.58 | 1.70 | 1.82 | 1.95
     =3=  | 2.07 | 2.21 | 2.34 | 2.48 | 2.61 | 2.76 | 2.90 | 3.05
     =4=  | 3.20 | 3.35 | 3.50 | 3.66 | 3.81 | 3.97 | 4.14 | 4.30
     =5=  | 4.47 | 4.64 | 4.81 | 4.98 | 5.15 | 5.33 | 5.51 | 5.69
     =6=  | 5.87 | 6.06 | 6.25 | 6.44 | 6.62 | 6.82 | 7.01 | 7.21
     =7=  | 7.40 | 7.60 | 7.80 | 8.01 | 8.21 | 8.42 | 8.63 | 8.83
     =8=  | 9.05 | 9.26 | 9.47 | 9.69 | 9.91 |10.13 |10.35 |10.57
     =9=  |10.80 |11.02 |11.25 |11.48 |11.71 |11.94 |12.17 |12.41
    =10=  |12.64 |12.88 |13.12 |13.36 |13.60 |13.85 |14.09 |14.34
    =11=  |14.59 |14.84 |15.09 |15.34 |15.59 |15.85 |16.11 |16.36
    =12=  |16.62 |16.88 |17.15 |17.41 |17.67 |17.94 |18.21 |18.47
    =13=  |18.74 |19.01 |19.29 |19.56 |19.84 |20.11 |20.39 |20.67
    =14=  |20.95 |21.23 |21.51 |21.80 |22.08 |22.37 |22.65 |22.94
    =15=  |23.23 |23.52 |23.82 |24.11 |24.40 |24.70 |25.00 |25.30
    =16=  |25.60 |25.90 |26.20 |26.50 |26.80 |27.11 |27.42 |27.72
    =17=  |28.03 |28.34 |28.65 |28.97 |29.28 |29.59 |29.91 |30.22
    =18=  |30.54 |30.86 |31.18 |31.50 |31.82 |32.15 |32.47 |32.80
    =19=  |33.12 |33.45 |33.78 |34.11 |34.44 |34.77 |35.10 |35.44
    =20=  |35.77 |36.11 |36.45 |36.78 |37.12 |37.46 |37.80 |38.15
  --------+------+------+------+------+------+------+------+------

            NOTE.--The weir table on this page contains
          figures 1, 2, 3, etc., in the first vertical
          column which indicates the inches depth of water
          running over weir board notches. Frequently the
          depths measured represent also fractional inches,
          between 1 and 2, 2 and 3, etc. The horizontal
          line of fraction at the top represents these
          fractional parts, and can be applied between any
          of the numbers of inches depth, from 1 to 25. The
          body of the table shows the cubic feet, and the
          fractional parts of a cubic foot, which will pass
          each minute for each inch in depth, and for each
          fractional part of an inch by eighths for all
          depths from 1 to 25 inches. Each of these results
          is for only one inch width of weir. To estimate
          for any width of weir the result obtained for one
          inch width must be multiplied by the number of
          inches constituting the whole horizontal length
          of weir.

[Illustration: FIGS. 2,760 and 2,761.--Samson vertical runner and
shaft, and complete Samson vertical turbine. The runner is composed
of two separate and distinct types of wheel, having thereby also
two diameters. Each wheel or set of buckets receives its separate
quantity of water from one and the same set of guides, but each set
acts only once and singly upon the water used, and the water does not
act twice upon the combined wheel, as some suppose. In construction=,
the lower or main set of buckets is made of flanged plate steel, and
cast solidly into a heavy ring surrounding the outer and lower edges,
and into a heavy diaphragm, separating the two sets of buckets.]

[Illustration: FIG. 2,762.--Water discharging from a needle nozzle
due to a pressure of 169 lbs. per sq. in.]

=Hydro-Electric Plants.=--The economy with which electricity can be
transmitted long distances by high tension alternating currents, has
led to the development of a large number of water powers in more or
less remote regions.

[Illustration: FIG. 2,763.--Photograph of an operating tangential
water wheel equipped with Pelton buckets.]

     This economy is possible by the facility with which alternating
   current can be transformed up and down. Thus at the hydro-electro
   plant, the current generated by the water wheel driven alternator
   is transformed to very high pressure and transmitted with economy
   a long distance to the distributing point where it is transformed
   down to the proper pressure for distribution.

     A water wheel or turbine is a machine in which a rotary motion
   is obtained by transference of the momentum of water; broadly
   speaking, the fluid is guided by fixed blades, attached with a
   casing, and impinging on other blades mounted on a drum or shaft,
   causing the latter to revolve.

     There are two general classes of turbine:
        1. Impulse turbines;
        2. Reaction turbines.


[Illustration: FIG. 2,764.--Sectional elevation of one of the 5,000
horse power vertical Pelton-Francis turbines directly connected to
generator, as installed for the Schenectady Power Co.]

=Ques. What is an impulse turbine?=

Ans. One in which the fluid is directed by means of a series of
nozzles against vanes which it drives.

=Ques. What is a reaction turbine?=

Ans. One in which the pressure or head of the water is employed
rather than its velocity. The current is deflected upon the wheel by
the action of suitably disposed guide blades, the passages being full
of water. Rotary motion is obtained by the change in the direction
and momentum of the fluid.

[Illustration: Figs. 2,765 to 2,768.--Cross sections of Lowel dam
power house, and wheel pits containing sixteen Samson turbines: The
section C-D gives an end view of the generator room showing the
locations of the generators below the head level water. They are
secure against flood water, or leakage, by well constructed stuffing
boxes in the iron bulkheads, through which the turbine wheel shafts
pass and connect to the generators. Section E-F gives an end view of
one of these wheel rooms or penstocks, and shows the extension of the
draft tube from wheel case into tail water. The section A-B shows the
sub-structure of gravel and macadam under the controlling gates, this
forming also a portion or extension of the dam proper. These gates
turn on an axis made of two 15 inch I beams securely riveted together
with plates and angle irons to which the wooden frame is attached.
The radius of the gates is 14 feet. They are designed to allow the
water to pass underneath the gate, thus controlling any height of
head water. They are intended to take care of an excess of water at
unusual stages of the river. The whole affair has been well designed
and executed. This plant furnishes a good example of a secure, and
level foundation, since the wheel houses and generator room are
immediately on the rock. It is necessary in all tandem plants to
provide a very secure, substantial super-structure so that the long
line of turbines and shaft will always remain straight and in proper
alignment with the generator and the turbine cases. Users cannot be
reminded of this too often.]

=Ques. Name three classes of reaction turbines.=

Ans. Parallel flow, inward flow, and outward flow.

     Parallel flow turbines have an efficiency of about 70% and are
   suited for low falls not over 30 feet. Inward and outward flow
   turbines have an efficiency of about 85%. Impulse turbines are
   suitable for high heads.

[Illustration: FIGS. 2,769 and 2,770.--Exterior and interior of
hydro-electric plant at Harrisburg, Va. It is located on the south
fork of the Shenandoah River, twelve and one-half miles distant. A
dam 720 feet long and 15 feet high was built on a limestone ledge
running across the river; which with a fall of 5 feet from the dam to
the power house, a quarter of a mile distant, secured an effective
head pressure of 20 feet. The power house, comprising the generator
room and the wheel room, also the machinery room, are here shown. The
wheel room, which is 20 × 40 feet, extends across the head race, and
rests upon solid concrete walls, forming the sides and ends of the
wheel pits. The end wall is 6 feet thick at the bottom, and 4½ feet
at the top. It has three arched openings, each 8 feet wide and 9 feet
high, through which the water escapes after leaving the turbines.
The intake is protected by a wrought iron rack 40 feet long. The
power is obtained by three 50 inch vertical shaft Samson turbines,
with a 20 inch Samson for an exciter. The three large turbines
have a rating of 1,350 horse power; and are connected to the main
horizontal line shaft by bevel mortise gears 7 feet diameter and 15
inches face. The couplings on the main shaft have 48 inch friction
clutch hubs, permitting either or each turbine being operated, or
shut down independently of the others. The main shaft is 85 feet long
and 6 inches diameter; making 280 revolutions. This shaft carries
two pulleys 70 inches diameter and 38 inches face for driving the
generators. The accompanying illustration shows the harness work,
gears, pulleys, etc., furnished with the turbines. The 20 inch
horizontal shaft Samson turbine of 72 horse power is direct connected
to an exciter generator of 20 kw., running 700 rev. per min. The
two large generators are driven 450 revolutions per minute by belts
producing a three phase current of 60 cycles of 11,500 volts for the
twelve and one-half miles transmission. The line consists of three
strands of No. 4 bare copper wire. This current is used for lighting
and power purposes, and the plant is of the latest improved design
and construction.]

=Isolated Plants.=--When electric power transmission from central
stations first came into commercial use, the distance from the
station at which current could be obtained at a reasonable cost was
exceedingly limited.

[Illustration: FIG. 2,769a.--Triumph direct current generator set with
upright slide valve engine.]

[Illustration: FIG. 2,770a.--Murray alternating current direct
connected unit with high speed Corliss engine and belt driven
exciter, 50, 75 and 100 kva. alternator and 150 R.P.M. engine.]

[Illustration: FIG. 2,771.--Direct connected direct current unit with
Ridgway high speed four valve engine.]

[Illustration: FIG. 2,772.--Buckeye mobile, or self contained unit
consisting of compound condensing engine, boiler, superheater,
reheater, feed and air pumps; it produces one horse power on 1½ lbs.
of coal, built in sizes from 75 to 600 horse power.]

[Illustration: FIG. 2,773.--Westinghouse three cylinder gas engine,
direct connected to dynamo, showing application of gas engine drive
for small direct connected units.]

     Consequently, persons desiring electrical power were in the
   majority of cases forced to install their own apparatus for
   producing it, this being the origin of isolated plants.

     From the nature of the case it is evident that an isolated
   plant is as a rule smaller and more simple in construction than
   a central station, and in consequence much more readily operated
   and managed. It is generally owned by a private individual or a
   corporation and operated in conjunction with other affairs of a
   similar character. A basement or other portion of a building is
   usually set aside in which the necessary apparatus is installed.

[Illustration: FIG. 2,774.--General Electric 25 kw., gasoline
electric generating set for lighting and power. The engine has
four cylinders 7¼ × 7½, and runs at a speed of 560 revolutions per
minute. The total candle power capacity in Mazda lamps is 20,000. The
ignition is by low tension magneto, coil and battery. Carburetter is
of the constant level type to which gasoline is delivered by a pump
driven by the engine. Forced lubrication; five crank shaft bearings
babbitted; valves in side; overall dimensions 96 × 34 × 60 high;
weight 5,000.]

     Although electricity is now transmitted economically to great
   distances from central stations, there is still a field for the
   isolated plant.

     The average type of isolated plant has enlarged from a small
   dynamo driven by a little slide valve engine located in an out
   of the way corner to direct connected generators and engines of
   hundreds and even thousands of horse power assembled in a large
   room specially adapted to the purpose.

     In the more modern of these, the electrical outputs are each
   frequently equal to that of a town central station of respectable
   size, and the auxiliary equipments are similar in every
   particular. As a matter of fact, in certain modern isolated plants
   the only feature that distinguishes them from central stations
   is that in the former case the owner of the plant represents the
   sole consumer and conducts other business in connection with it,
   whereas in the latter case there are a large number of consumers
   uninterested financially in the enterprise, which is itself
   generally owned and operated by a company conducting no other
   business.

[Illustration: FIG. 2,775.--Plan of sub-station with air blast
transformers and motor operated oil switches and underground 11,000
or 13,200 volt high tension lines.]

=Sub-Stations.=--According to the usual meaning of the term, a
sub-station is a building provided with apparatus for changing high
pressure alternating current received from the central station into
direct current of the requisite pressure, which in the case of
railways is 550 to 600 volts.

Where traffic is heavy and the railway system of considerable
distance, sub-stations are provided at intervals along the line,
each receiving high pressure current from one large central station
and converting it into moderate pressure direct current for their
districts.

=Ques. Upon what does the arrangement of the sub-station depend?=

Ans. Upon the character of the work and the type of apparatus
employed for converting the high pressure alternating current into
direct current.

[Illustration: FIG. 2,776.--Plan of small sub-station with single
phase oil insulated self-cooling transformers and hand operated oil
switches 11,000 or 13,200 volts, overhead high tension lines.]

     In general it should be substantial, convenient to install or
   replace the heavy machines, and the layout arranged so that the
   apparatus can be readily operated by those in attendance.

     An overhead traveling crane is the most convenient method of
   handling the heavy machinery, and is frequently used in large
   sub-stations.

     Fig. 2,776 shows a sectional view, and fig. 2,777, a plan for
   a small sub-station containing two rotary converters and two
   banks of three single phase static transformers operating on a
   three phase system at 11,000 or 13,200 volts, together with the
   auxiliary apparatus.

[Illustration: FIG. 2,777.--Elevation of small sub-station, as shown
in plan in Fig. 2,776.]

=Ques. For three phase installations, what are the merits of
separate and combined transformers?=

Ans. With separate transformer for each phase, repairs are more
readily made in case of accident or burnouts in the coils. The three
phase units have the advantage of low first cost.

     Sub-station transformers produce considerable heat, due to the
   hysteresis and eddy currents, and it is necessary to get rid of it.

     Small transformers radiate the heat from the shell and the
   medium sizes have corrugated shells which increase the surface and
   provide more rapid radiation.

     Large transformers are cooled by an air blast supplied by motor
   driven blowers or by water pumped through a coil of pipe which is
   immersed in the insulating oil of the transformer. The large size
   oil insulated, water cooled transformers are used on circuits of
   33,000 volts or more. In water turbine plants, the water may be
   piped to the transformer under pressure and the pump omitted which
   cuts down the cost of operating. Air blast transformers usually
   have a damper or shutter for air control.

[Illustration: FIG. 2,778.--Marine portable transformer station on
Los Angeles Aqueduct. The view shows three 20 kva. Westinghouse out
door transformers installed on a float, 33,000 volts high pressure;
440 volts low pressure; 50 cycles.]

=Ques. Explain the use of reactance coils in sub-stations.=

Ans. In order that the direct current voltage of the ordinary rotary
may be regulated by a field rheostat, which calls for a corresponding
change in the alternating current voltage, a reactance coil is
provided between the low tension winding and the converter.

     Without such a reactance the maintenance of the same voltage at
   full load as at no load involves excessive leading and lagging
   currents and consequently excessive heating in the armature
   inductors, unless the resistance drop from the source of constant
   pressure is small, or the natural reactance of the circuit high.

=Ques. What is the effect of weakening the converter field?=

Ans. A lagging current is set up which causes a drop in the reactance
coil.

[Illustration: FIG. 2,779.--Sectional elevation of portable outdoor
transformer type sub-station. The high voltage switching and
protective apparatus is mounted, out of the way, on the roof of the
car, but is operated from the switchboard with a standard remote
control handle. The transformer is carried directly over the truck at
the uncovered end of the car and the low-tension leads from it run in
conduit beneath the floor and up into the cab, (which contains the
converter and switchboard) to the converter. The positive lead runs
through a conduit and ends in a terminal on the roof. The energy thus
makes a complete circuit of the car leaving at a point close to that
at which it entered. The low pressure alternating current as well as
the direct current positive leads are carried below the car floor
in iron conduit supported from the channel frame. The field wires
are carried through this conduit to the rheostat. Wiring for the
lights is arranged to supply two, 5 light clusters. One is fed with
the 600 volt direct current and the other with 420 volt alternating
current. All lighting conductors are carried in metal moulding
carried between the flanges of the channel iron ribs. High wiring
is carried entirely on the roof of the car where it is entirely out
of the way and where the operator cannot come in contact with it.
The switchboard should be of the utmost simplicity. Usually the
negative and equalizer switches, and the field break-up switch are
mounted on the frame of the converter. The double throw switch for
starting and running the converter can be mounted under the floor
of the car and operated by handle at the switchboard. The rheostat
can be mounted back of the switchboard on brackets bolted to the car
super-structure. The switchboard need only carry the positive knife
switch and circuit breaker, and the alternating current ammeter,
voltmeter and power factor meter. Sometimes a watthour meter is
added. The positive lead is brought out through a conduit on the
roof of the car and is arranged for bolting to the positive feeder.
The negative and equalizer terminals are located at the cab end of
the car and are arranged so that connection can be easily made from
them to the ground and, if necessary, to an equalizer circuit. There
is usually a sliding door at each end of the cab and two windows on
each side. Above the doors, transoms, extending the width of the cab,
are arranged to drop so that a current of air will circulate through
the cab under the roof, carrying out the heated air. There are also
several ventilating holes beneath the converter in the floor of the
car. These provisions insure a constant circulation of air through
the car which carries away all heated air.]

=Ques. State the effect of strengthening converter field.=

Ans. A leading current is set up which gives a rise of voltage in the
reactance coil.

     Hence when a heavy current passes through the series coil of a
   compound wound converter and tends to produce a leading current,
   the reactance coil will balance it, and improve the power factor
   of the whole line.

[Illustration: FIG. 2,780.--Westinghouse 300 kw. converter in
portable sub-station.]

=Portable Sub-Stations.=--A portable sub-station constitutes a spare
equipment for practically any number of permanent sub-stations and
renders unnecessary the installation of spare equipment in each.

     It can be used to increase the capacity of a permanent
   sub-station when the load is unusually heavy, or to provide
   service while a permanent sub-station is being overhauled or
   rebuilt.

     The transformer can be used for emergency lighting, the primary
   being connected to a high pressure line and the secondary to the
   load, if special provision be made at the time the transformer is
   built to adapt it for these applications.

[Illustration: FIG. 2,781.--Switchboard end of Westinghouse portable
sub-station.]

When an electric railway has a portable sub-station, direct current
can be provided at any point on the system where there is track at
the high pressure line. The direct current can be made available
very quickly as its production involves only the transferring of the
sub-station, and its connection to the high pressure line.

     Portable sub-stations range in capacity from 200 to 500 kw., and
   for all alternating current voltages up to 66,000, and frequencies
   of 25 and 60 cycles.

     Although portable sub-stations usually must be of more or
   less special design to adapt them to the conditions under which
   they must operate, there are certain general features that are
   common to all. All members are readily accessible and there are
   no unnecessary parts. The weight and dimensions are a minimum
   insuring ease of transportation. Live parts are so protected that
   the danger of accidental contact with them is minimized.

[Illustration: FIGS. 2,782 and 2,783.--Views of levelling device for
Westinghouse converter.]

=Ques. What are the advantages of using outdoor transformers on
portable sub-stations?=

Ans. All high pressure wiring is kept out of the car. The transformer
is more effectively cooled and the heat dissipated by the transformer
does not warm the interior of the cab. The transformer is much more
accessible. The car can be run under a crane and the transformer
coils pulled out with a hoist.

     Taps for different high and low pressure voltages can be readily
   provided at the time the transformer is being built.



CHAPTER LXVII

MANAGEMENT


The term "management," broadly speaking, includes not only the
actual skilled attention necessary for the proper operation of the
machines, after the plant is built, but also other duties which must
be performed from its inception to completion, and which may be
classified as

  1. Selection;
  2. Location;
  3. Erection;
  4. Testing;
  5. Running;
  6. Care;
  7. Repair.

That is to say, someone must select the machinery, determine where
each machine is to be located, install them, and then attend to the
running of the machines and make any necessary repairs due to the
ordinary mishaps likely to occur in operation.

These various duties are usually entrusted to more than one
individual; thus, the selection and location of the machinery is done
by the designer of the plant, and requires for its proper execution
the services of an electrical engineer, or one possessing more than
simply a practical knowledge of power plants.

The erection of the machines is best accomplished by those making a
specialty of this line of work, who by the nature of the undertaking
acquire proficiency in methods of precision and an appreciation of
the value of accuracy which is so essential in the work of aligning
the machines, and which if poorly done will prove a constant source
of annoyance afterward.

The attention required for the operation of the machines, embracing
the running care and repair, is left to the "man in charge," who
in most cases of small and medium size plants is the chief steam
engineer. He must therefore, not only understand the steam apparatus,
but possess sufficient knowledge of electrical machinery to operate
and maintain it in proper working order.

The present chapter deals chiefly with alternating current machinery,
the management of direct current machines having been fully explained
in Guide No. 3, however, some of the matter here presented is common
to both classes of apparatus.

       *       *       *       *       *

=Selection.=--In order to intelligently select a machine so that it
will properly harmonize with the conditions under which it is to
operate, there are several things to be considered.

  1. Type;
  2. Capacity;
  3. Efficiency;
  4. Construction.

The general type of machine to be used is, of course, dependent on
the system employed, that is, whether it be direct or alternating,
single or polyphase.

     Thus, the voltage in most cases is fixed except on transformer
   systems where a choice of voltage may be had by selecting a
   transformer to suit.

In alternating current constant pressure transmission circuits, an
average voltage of 2,200 volts with step down transformer ratios of
1/10 and 1/20 is in general use, and is recommended.

     For long distance, the following average voltages are
   recommended 6,000; 11,000; 22,000; 33,000; 44,000; 66,000; 88,000;
   and higher, depending on the length of the line and degree of
   economy desired.

In alternating circuits the standard frequencies are 25, and 60
cycles. These frequencies are already in extensive use and it is
recommended to adhere to them as closely as possible.

[Illustration: FIG. 2,784.--Diagram of connections for testing to
obtain the saturation curve of an alternator. The saturation curve
shows the relation between the volts generated in the armature and
the amperes of field current (or ampere turns of the field) for a
constant armature current. The armature current may be zero, in which
case the curve is called _no load saturation curve_, or sometimes the
_open circuit characteristic curve_. A saturation curve may be taken
with full load current in the armature; but this is rarely done,
except in alternators of comparatively small output. If a full load
saturation curve be desired, it can be approximately calculated from
the no load saturation curve. The figure shows the connections. If
the voltage generated is greater than the capacity of the voltmeter,
a multiplying coil or a step down pressure transformer may be used,
as shown. A series of observations of the voltage between the
terminals of one of the phases, is made for different values of the
field current. Eight or nine points along the curve are usually
sufficient, the series extending from zero to about fifty per cent.
above normal rated voltage. The points should be taken more closely
together in the vicinity of normal voltage than at other portions of
the curve. Care must be taken that the alternator is run at its rated
speed, and this speed must be kept constant. Deviations from constant
speed may be most easily detected by the use of a tachometer. If the
machine be two phase or three phase, the voltmeter may be connected
to any one phase throughout a complete series of observations. The
voltage of all the phases should be observed for normal full load
excitation by connecting the voltmeter to each phase successively,
keeping the field current constant at normal voltage. This is done in
order to see how closely the voltage of the different phases agree.]

     In fixing the capacity of a machine, _careful consideration
   should be given to the conditions of operation both_ =present=
   _and_ =future= in order that the resultant efficiency may be
   maximum.

     Most machines show the best efficiency at or near full load.
   If the load be always constant, as for instance, a pump forcing
   water to a given head, it would be a simple matter to specify the
   proper size of machine, but in nearly all cases, and especially
   in electrical plants, the load varies widely, not only the daily
   and hourly fluctuations, but the varying demands depending on
   the season of the year and growth of the plant's business. All
   of these conditions tend to complicate the matter, so that
   intelligent selection of capacity of a machine requires not only
   calculation but mature judgment, which is only obtained by long
   experience.

[Illustration: FIG. 2,785.--Saturation curve taken from a 2,000 kw.,
three phase alternator of the revolving field type, having 16 poles,
and generating 2,000 volts, and 576 amperes per phase when run at 300
R.P.M.]

In selecting a machine, or in fact any item connected with the plant
_its construction should be carefully considered_.

     Standard construction should be insisted upon so that in the
   event of damage a new part can be obtained with the least possible
   delay.

     The parts of most machines are _interchangeable_, that is to
   say, with the refined methods of machinery a duplicate part
   (usually carried in stock) may be obtained at once to replace a
   defective or broken part, and made with such precision that little
   or no fitting will be required.

The importance of standard construction cannot be better illustrated
than in the matter of steam piping, that is, the kind of fittings
selected for a given installation.

With the exception of the exhaust line from engine to condenser,
where other than standard construction may sometimes be used to
reduce the frictional resistance to the steam, the author would
adhere to standard construction except in very exceptional cases.
Those who have had practical experience in pipe fitting will
appreciate the wisdom of this.

For installations in places remote from large supply houses, the more
usual forms of standard fittings should be employed, such as ordinary
T's, 45° and 90° elbows, etc.

In such locations, where designers specify the less usual forms of
standard fittings such as union fittings, offset reducers, etc.,
or special fittings made to sketch, it simply means, in the first
instance that they usually cannot be obtained of the local dealer,
making it necessary to order from some large supply house and
resulting in vexatious delays.

As a rule, those who specify special fittings have found that their
making requires an unreasonable length of time, and the cost to be
several times that of the equivalent in standard fittings.

An examination of a few installations will usually show numerous
special and odd shape fittings, which are entirely unnecessary.

Moreover, a standard design, in general, is better than a special
design, because the former has been tried out, and any imperfection
or weakness remedied, and where thousands of castings of a kind are
turned out, a better article is usually the result as compared with a
special casting.

In the matter of construction, in addition to the items just
mentioned, it should be considered with respect to

  1. Quality;
  2. Range;
  3. Accessibility;
  4. Proportion;
  5. Lubrication;
  6. Adjustment.

It is poor policy, excepting in very rare instances, to buy a "cheap"
article, as, especially in these days of commercial greed, the best
is none too good.

[Illustration: FIGS. 2,786 and 2,787.--Wheel and roller pipe cutters
illustrating =range=. The illustrations show the comparative
movements necessary with the two types of cutter to perform their
function. The wheel cutter requiring only a small arc of movement
will cut a pipe in an inaccessible place as shown, which with a
roller cutter would be impossible. Accordingly, the wheel cutter is
said to have a greater _range_ than the roller cutter.]

Perhaps next in importance to quality, at least in most cases,
is _range_. This may be defined as _scope of operation_,
_effectiveness_, or _adaptability_. The importance of range is
perhaps most pronounced in the selection of tools, especially for
plants remote from repair shops.

     For instance, in selecting a pipe cutter, there are two general
   classes: wheel cutters, and roller cutters. A wheel cutter has
   three wheels and a roller cutter one wheel and two rollers, the
   object of the rollers being to keep the wheel perpendicular to
   the pipe in starting the cut and to reduce burning. It must be
   evident that in operation, a roller cutter requires sufficient
   room around the pipe to permit making a complete revolution of
   the cutter, whereas, with a wheel cutter, the work may be done
   by moving the cutter back and forth through a small arc, as
   illustrated in figs. 2,786 and 2,787. Thus a wheel cutter has a
   _greater range_ than a roll cutter.

     Range relates not only to ability to operate in inaccessible
   places but to the various operations that may be performed by one
   tool.

       PROPERTIES OF STANDARD WROUGHT IRON PIPE

  --------------------------+------+-----------------+
                            |      |                 |
                            |      |                 |
                            |      |                 |
                            |      |                 |
           Diameter         |Thick-|  Circumference. |
                            | ness.|                 |
  --------+--------+--------+      +--------+--------+
   Nominal| Actual | Actual |      |External|Internal|
  internal|external|internal|      |        |        |
  --------+--------+--------+------+--------+--------+
   Inches | Inches | Inches |Inches| Inches | Inches |
  --------+--------+--------+------+--------+--------+
       ⅛  |   .405 |   .27  | .068 |  1.272 |   .848 |
       ¼  |   .54  |   .364 | .088 |  1.696 |  1.144 |
       ⅜  |   .675 |   .494 | .91  |  2.121 |  1.552 |
       ½  |   .84  |   .623 | .109 |  2.639 |  1.957 |
       ¾  |  1.05  |   .824 | .113 |  3.299 |  2.589 |
      1   |  1.315 |  1.048 | .134 |  4.131 |  3.292 |
      1¼  |  1.66  |  1.38  | .14  |  5.215 |  4.335 |
      1½  |  1.9   |  1.611 | .145 |  5.969 |  5.061 |
      2   |  2.375 |  2.067 | .154 |  7.461 |  6.494 |
      2½  |  2.875 |  2.468 | .204 |  9.032 |  7.753 |
      3   |  3.5   |  3.067 | .217 | 10.996 |  9.636 |
      3½  |  4.    |  3.548 | .226 | 12.566 | 11.146 |
      4   |  4.5   |  4.026 | .237 | 14.137 | 12.648 |
      4½  |  5.    |  4.508 | .246 | 15.708 | 14.162 |
      5   |  5.563 |  5.045 | .259 | 17.477 | 15.849 |
      6   |  6.625 |  6.065 | .28  | 20.813 | 19.054 |
      7   |  7.625 |  7.023 | .301 | 23.955 | 22.063 |
      8   |  8.625 |  7.982 | .322 | 27.096 | 25.076 |
      9   |  9.625 |  8.937 | .344 | 30.238 | 28.076 |
     10   | 10.75  | 10.019 | .366 | 33.772 | 31.477 |
     11   | 12.    | 11.25  | .375 | 37.699 | 35.343 |
     12   | 12.75  | 12.    | .375 | 40.055 | 37.7   |
  --------+--------+--------+------+--------+--------+
------+-------------------------+---------------+--------+-------+------
      |                         |               |        |       |
      |                         |               |        |       |
      |                         |               | Length |       |
      |                         |Length of pipe |of pipe |Nominal|
 Diam.|     Transverse areas.   |  per square   |contain-|weight |Number
      |                         |    foot of    |ing one | per   |  of
------+--------+--------+-------+-------+-------+ cubic  | foot. |thread
 Nom. |External|Internal| Metal |Ext'nal|Int'nal|  foot. |       | per
intern|        |        |       |surface|surface|        |       | inch
------+--------+--------+-------+-------+-------+--------+-------+ of
Inches|Sq. ins.|Sq. ins.|Sq.ins.|  Feet |  Feet |  Feet  |Pounds |screw
------+--------+--------+-------+-------+-------+--------+-------+-----
    ⅛ |   .129 |   .0573|  .0717| 9.44  |14.15  |2513.   |  .241 | 27
    ¼ |   .229 |   .1041|  .1249| 7.075 |10.49  |1383.3  |  .42  | 18
    ⅜ |   .358 |   .1917|  .1663| 5.657 | 7.73  | 751.2  |  .559 | 18
    ½ |   .554 |   .3048|  .2492| 4.547 | 6.13  | 472.4  |  .837 | 14
    ¾ |   .866 |   .5333|  .3327| 3.637 | 4.635 | 270.   | 1.115 | 14
   1  |  1.358 |   .8626|  .4954| 2.904 | 3.645 | 166.9  | 1.668 | 11½
   1¼ |  2.164 |  1.496 |  .668 | 2.301 | 2.768 |  96.25 | 2.244 | 11½
   1½ |  2.835 |  2.038 |  .797 | 2.01  | 2.371 |  70.66 | 2.678 | 11½
   2  |  4.43  |  3.356 | 1.074 | 1.608 | 1.848 |  42.91 | 3.609 | 11½
   2½ |  6.492 |  4.784 | 1.708 | 1.328 | 1.547 |  30.1  | 5.739 |  8
   3  |  9.621 |  7.388 | 2.243 | 1.091 | 1.245 |  19.5  | 7.536 |  8
   3½ | 12.566 |  9.887 | 2.679 |  .955 | 1.077 |  14.57 | 9.001 |  8
   4  | 15.904 | 12.73  | 3.174 |  .849 |  .949 |  11.31 |10.665 |  8
   4½ | 19.635 | 15.961 | 3.674 |  .764 |  .848 |   9.02 |12.34  |  8
   5  | 24.306 | 19.99  | 4.316 |  .687 |  .757 |   7.2  |14.502 |  8
   6  | 34.472 | 28.888 | 5.584 |  .577 |  .63  |   4.98 |18.762 |  8
   7  | 45.664 | 38.738 | 6.926 |  .501 |  .544 |   3.72 |23.271 |  8
   8  | 58.426 | 50.04  | 8.386 |  .443 |  .478 |   2.88 |28.177 |  8
   9  | 72.76  | 62.73  |10.03  |  .397 |  .427 |   2.29 |33.701 |  8
  10  | 90.763 | 78.839 |11.924 |  .355 |  .382 |   1.82 |40.065 |  8
  11  |113.098 | 99.402 |13.696 |  .318 |  .339 |   1.450|45.95  |  8
  12  |127.677 |113.098 |14.579 |  .299 |  .319 |   1.27 |48.985 |  8
------+--------+--------+-------+-------+-------+--------+-------+----

Open construction should be employed, wherever possible, so that
all parts of a machine that require attention, or that may become
deranged in operation, may be accessible for adjustment or repair.

     The design should be such that there is ample strength, and the
   bearings for moving parts should be of liberal proportions to
   avoid heating with minimum attention.

     A comparison of the proportions used by different manufacturers
   for a machine of given size might profitably be made before a
   selection is made.

The matter of lubrication is important.

     Fast running machines, such as generators and motors, should be
   provided with ring oilers and oil reservoirs of ample capacity, as
   shown in figs. 2,788 to 2,794.

[Illustration: FIG. 2,788.--Sectional view showing a ring oiler or
self oiling bearing. As shown the pedestal or bearing standard is
cored out to form a reservoir for the oil. The rings are in rolling
contact with the shaft, and dip at their lower part into the oil.
In operation, oil is brought up by the rings which revolve because
of the frictional contacts with the shaft. The oil is in this way
brought up to the top of the bearing and distributed along the shaft
gradually descending by gravity to the reservoir, being thus used
over and over. A drain cock, is provided in the base so that the oil
may be periodically removed from the reservoir and strained to remove
the accumulation of foreign matter. This should be frequently done to
minimize the wear of the bearing.]

All bearings subject to appreciable wear should be made adjustable so
that lost motion may be taken up from time to time and thus keep the
vibration and noise of operation within proper limits.

=Selection of Generators.=--This is governed by the class of work
to be done and by certain local conditions which are liable to vary
considerably for different stations.

These variable factors determine whether the generators must be of
the direct or alternating current type, whether they must be wound
to develop a high or a low voltage, and whether their outputs in
amperes must be large or small. Sufficient information has already
been given to cover these various cases; there are, however, certain
general rules that may advantageously be observed in the selection of
generators designed to fill any of the aforementioned conditions, and
it is well to possess certain facts regarding their construction.

[Illustration: FIGS. 2,789 to 2,794.--Self oiling self aligning
bearing open. Views showing oil grooves, rings, bolts etc.]

=Ques. Name an important point to be considered in selecting a
generator.=

Ans. Its efficiency.

=Ques. What are the important points with respect to efficiency?=

Ans. A generator possessing a high efficiency at the average load is
more desirable than a generator showing a high efficiency at full
load.

=Ques. Why?=

Ans. The reason is that in station practice the full load limit is
seldom reached, the usual load carried by a generator ordinarily
lying between the one-half and three-quarter load points.

=Ques. How do the efficiencies of large and small generators compare?=

Ans. There is little difference.

[Illustration: FIG. 2,795.--Rotor of Westinghouse type T turbine
dynamo set. The dynamo is of the commutating pole type either shunt
or compound wound. The turbine is of the single wheel impulse type.
The wheel is mounted directly on the end of the shaft as shown. Steam
is used two or more times on the wheel to secure efficiency. A fly
ball governor is provided with weights hung on hardened steel knife
edges. In case of over speeding, an automatic safety stop throttle
valve is tapped shutting off the steam supply. This type of turbine
dynamo set is especially applicable for exciter service in modern,
superheated steam generating stations where the steam pressure
exceeds 125 pounds. Westinghouse Type T turbines operate directly
(that is, without a reducing valve) on pressures up to 200 pounds per
square inch with steam superheated to 150 degrees Fahrenheit.]

=Ques. How are the sizes and number of generator determined?=

Ans. The sizes and number of generator to be installed should be
such as to permit the engines operating them being worked at nearly
full load, because the efficiencies of the latter machines decrease
rapidly when carrying less than this amount.

=Ques. What is understood by regulation?=

Ans. The accuracy and reliability with which the pressure or current
developed in a machine may be controlled.

     It is generally possible if purchasing of a reputable concern,
   to obtain access to record sheets on which may be found results
   of tests conducted on the generator in question, and as these are
   really the only means of ascertaining the values of efficiency and
   regulation, the purchaser has a right to inspect them. If, for
   some reason or other, he has not been afforded this privilege, he
   should order the machine installed in the station on approval, and
   test its efficiency and regulation before making the purchase.

[Illustration: FIG. 2,796.--Cross section of electrical station
showing small traveling crane.]

=Installation.=--The installation of machines and apparatus in an
electrical station is a task which increases in difficulty with
the size of the plant. When the parts are small and comparatively
light they may readily be placed in position, either by hand, by
erecting temporary supports which may be moved from place to place
as desired, or by rolling the parts along on the floor upon pieces
of iron pipe. If, however, the parts be large and heavy, a traveling
crane such as shown in fig. 2,797, becomes necessary.

=Ques. What precaution should be taken in moving the parts of
machines?=

Ans. Care should be taken not to injure the bearings and shafts, the
joints in magnetic circuits such as those between frame and pole
pieces, and the windings on the field and armature.

[Illustration: FIG. 2,797.--Cross section of electrical station
showing a traveling crane for the installation or removal of large
and heavy machine parts. A traveling crane consists of an iron beam
which, being supplied with wheels at the ends, can be made to move
either mechanically or electrically upon a track running the entire
length of the station. This track is not supported by the walls
of the building, but rests upon beams specially provided for the
purpose. In addition to the horizontal motion thus obtained, another
horizontal motion at right angles to the former is afforded by means
of the carriage which, being also mounted on wheels, runs upon a
track on the top of the beam. Electrical power is generally used to
move the carriage and also the revolving drums contained thereon,
the latter of which give a vertical motion to the main hoist or the
auxiliary hoist, these hoists being used respectively for raising
or lowering heavy or light loads. In the larger sizes of electric
traveling crane, a cage is attached to the beam for the operator,
who, by means of three controllers mounted in the cage, can move a
load on either the main or auxiliary hoist in any direction.]

     The insulations of the windings are perhaps the most vital parts
   of a generator, and the most readily injured. The prick of a pin
   or tack, a bruise, or a bending of the wires by resting their
   weight upon them or by their coming in contact with some hard
   substance, will often render a field coil or an armature useless.

     Owing to its costly construction, it is advisable when
   transporting armatures by means of cranes to use a wooden
   spreader, as shown in fig. 2,798 to prevent the supporting rope
   bruising the winding.

[Illustration: FIG. 2,798.--View of armature in transit showing use
of a wooden spreader as a protection. If a chain be used in place of
the rope, a padding of cloth should be placed around the armature
shaft and special care taken that the chain does not scratch the
commutator.]

=Ques. If an armature cannot be placed at once in its final position
what should be done?=

Ans. It may be laid temporarily upon the floor, if a sheet of
cardboard or cloth be placed underneath the armature as a protection
for the windings; in case the armature is not to be used for some
time, it is better practice to place it in a horizontal position on
two wooden supports near the shaft ends.

=Ques. What kind of base should be used with a belt driven generator
or motor?=

Ans. The base should be provided with V ways and adjusting screws
for moving the machine horizontally to take up slack in the belt, as
shown in fig. 2,799.

     Owing to the normal tension on the belt, there is a moment
   exerted equal in amount to the distance from the center of gravity
   of the machine to the center of the belt, multiplied by the
   effective pull on the belt. This force tends to turn the machine
   about its center of gravity. By placing the screws as shown, any
   turning moment, as just mentioned, is prevented.

[Illustration: FIG. 2,799.--Plan of belt drive machine showing V ways
and adjusting screws for moving the machine forward from the engine
or counter shaft to take up slack in the belt.]

=Ques. How should a machine be assembled?=

Ans. The assembling should progress by the aid of a blue print, or by
the information obtained from a photograph of the complete machine
as it appears when ready for service. Each part should be perfectly
clean when placed in position, especially those parts between which
there is friction when the machine is in operation, or across which
pass lines of magnetic force; in both cases the surfaces in contact
must be true and slightly oiled before placing in position.

     Contact surfaces forming part of electrical circuits must also
   be clean and tightly screwed together. An important point to bear
   in mind when assembling a machine is, to so place the parts that
   it will not be necessary to remove any one of them in order to get
   some other part in its proper position. By remembering this simple
   rule much time will be saved, and in the majority of instances the
   parts will finally be better fitted together than if the task has
   to be repeated a number of times.

     When there are two or more parts of the machine similarly
   shaped, it is often difficult to properly locate them, but in such
   cases notice should be taken of the factory marks usually stamped
   upon such pieces and their proper places determined from the
   instructions sent with the machine.

[Illustration: FIGS. 2,800 to 2,802.--Starrett's improved speed
indicator. In construction, the working parts are enclosed like a
watch. The graduations show every revolution, and with two rows of
figures read both right and left as the shaft may run. While looking
at the watch, each hundred revolutions may be counted by allowing
the oval headed pin on the revolving disc to pass under the thumb as
the instrument is pressed to its work. A late improvement in this
indicator consists in the rotating disc, which, being carried by
friction may be moved to the starting point where the raised knobs
coincide. When the spindle is placed in connection with the revolving
shaft, pressing the raised knob with the thumb will prevent the disc
rotating, while the hand of the watch gets to the right position to
take the time. By releasing the pressure the disc is liberated for
counting the revolutions of the shaft when every 100 may be noted by
feeling the knob pass under the thumb lightly pressed against it,
thus relieving the eye, which has only to look on the watch to note
the time.]

=Ques. What should be noted with respect to speed of generator?=

Ans. Each generator is designed to be run at a certain speed in
order to develop the voltage at which the machine is rated. The
speed, in revolutions per minute, the pressure in volts, and the
capacity or output in watts (volts × amperes) or in kilowatts
(thousands of watts) are generally stamped on a nameplate screwed to
the machine.

     This requirement frequently requires calculations to be made by
   the erectors to determine the proper size pulleys to employ to
   obtain the desired speed.

[Illustration: FIG. 2,803.--Home made belt clamp. It is made with
four pieces of oak of ample size to firmly grip the belt ends where
the bolts are tightened. The figure shows the clamp complete and
in position on the belt and clearly illustrates the details of
construction. In making the long bolts the thread should be cut about
three-quarter length of bolt and deep enough so that the nuts will
easily screw on.]

     =Example.=--What diameter of engine pulley is required to run
   a dynamo at a speed of 1,450 revolutions per minute the dynamo
   pulley being 10 inches in diameter and the speed of engine, 275
   revolutions per minute?

The diameter of pulley required on engine is 10 × (1,450 ÷ 275) = 53
inches, nearly.

     =Rule.=--To find the diameter of the driving pulley, _multiply
   the speed of the driven pulley by its diameter, divide the product
   by the speed of the driver and the answer will be the size of the
   driver required_.

     _Example._--If the speed of an engine be 325 revolutions per
   minute, diameter of engine pulley 42 inches, and the speed of
   the dynamo 1,400 revolutions per minute, how large a pulley is
   required on dynamo?

     The size of the dynamo pulley is

42 × (325 ÷ 1,400) = 9¾ inches.

     =Rule.=--To find the size of dynamo pulley, _multiply the speed
   of engine by the diameter of engine wheel and divide the product
   by the speed of the dynamo_.

[Illustration: FIGS. 2,804 and 2,805.--A good method of lacing a
belt. The view at the left shows outer side of belt, and at the
right, inner or pulley side.]

     _Example._--If a steam engine, running 300 revolutions per
   minute, have a belt wheel 48 inches in diameter, and be belted
   to a dynamo having a pulley 12 inches in diameter, how many
   revolutions per minute will the dynamo make?

     The speed of dynamo will be 300 × (48 ÷ 12) = 1,200 rev. per min.

     =Rule.=--When the speed of the driving pulley and its diameter
   are known, and the diameter of the driven pulley is known, the
   speed of the driven pulley is found by _multiplying the speed of
   the driver by its diameter in inches and dividing the product by
   the diameter of the driven pulley_.

     =Example.=--What will be the required speed of an engine
   having a belt wheel 46 inches in diameter to run a dynamo 1,500
   revolutions per minute, the dynamo pulley being 11 inches in
   diameter?

     The speed of the engine is 1,500 × (11 ÷ 46) = 359 rev. per min.
   nearly.

[Illustration: FIG. 2,806.--Wiring diagram and directions for
operating Holzer-Cabot single phase self-starting motor. =Location:=
The motor should be placed in as clear and dry a location as
possible, away from acid or other fumes which would attack the
metal parts or insulation, and should be located where it is easily
accessible for cleaning and oiling. =Erection:= The motor should be
set so that the shaft is level and parallel with the shaft it is
to drive so that the belt will run in the middle of the pulleys.
Do not use a belt which is too heavy or too tight for the work it
has to do, as it will materially reduce the output of the motor.
The belt should be from one-half to one inch narrower than the
pulley. =Rotation:= In order to reverse the direction of rotation,
interchange leads A and B. =Suspended Motors:= Motors with ring oil
bearings may be used on the wall or ceiling by taking off end caps
and revolving 90 or 180 degrees until the oil wells come directly
below the bearings. =Starting:= Motors are provided with link across
two terminals on the upper right hand bracket at the front of the
motor and with this connection should start considerable overloads.
If the starting current be too great with this connection, it may be
reduced by removing the link. =Temperatures:= At full load the motor
will feel hot to the hand, but this is far below the danger point. If
too hot for touch, measure temperature with a thermometer by placing
bulb against field winding for 10 minutes, covering thermometer
with cloth or waste. The temperature should not exceed 75 degrees
Fahr. above the surrounding air. =Oiling:= Fill the oil wells to the
overflow before starting and keep them full. See that the oil rings
turn freely with shaft. =Care:= The motor must be kept clean. Smooth
collector rings with sandpaper and see that the brushes make good
contact. When brushes become worn they may be reversed. When fitting
new brushes or changing them always sandpaper them down until they
make good contact with the collector rings, by passing a strip of
sandpaper beneath the brush.]

     =Rule.=--To find the speed of engine when diameter of both
   pulleys, and speed of dynamo are given, _multiply the dynamo speed
   by the diameter of its pulley and divide by the diameter of engine
   pulley_.

=Ques. How are the diameters and speeds of gear wheels figured?=

Ans. The same as belted wheels, using either the pitch circle
diameters or number of teeth in each gear wheel.

[Illustration: FIGS. 2,807 to 2,809.--Wiring diagrams and directions
for operating Holzer-Cabot slow speed alternating current motors.
=Erecting:= In installing the motor, be sure the transformer and
wiring to the motor are large enough to permit the proper voltage
at the terminals. If too small, the voltage will drop and reduce
the capacity of the motor. =Oiling:= Maintain oil in wells to the
overflow. =Starting: Single phase= motors are started by first
throwing the starting switch down into the starting position, and
when the motor is up to speed, throwing it up into the running
position. _Do not hold the switch in starting position over 10
seconds._ Starter for single phase motors above ½ H.P. are arranged
with an adjusting link at the bottom of the panel. The link is shown
in the position of least starting torque and current. Connect from
W to 2 or W to 3 for starting heavier loads. _Two or three phase_
motors are started simply by closing the switch. These motors start
full load without starters. The motor should start promptly on
closing the switch. It should be started the first time without
being coupled to the line shaft. If the motor start free, but will
not start loaded, it shows either that the load upon the motor is
too great, the line voltage too low, or the frequency too high. The
voltage and frequency with the motor running should be within 5% of
the name plate rating and the voltage with 10 to 15% while starting.
If the motor do not start free, either it is getting no current or
something is wrong with the motor. In either case an electrician
should be consulted. =Solution:= To reverse the direction of rotation
interchange the leads marked "XX" in the diagrams. =Temperature:= At
full load the motor should not heat over 75 degrees Fahr. above the
temperature of the surrounding air; if run in a small enclosed space
with no ventilation, the temperature will be somewhat higher.]

=Ques. What should be noted with respect to generator pulleys?=

Ans. A pulley of certain size is usually supplied with each generator
by its manufacturer, and it is not generally advisable to depart much
from the dimensions of this pulley. Accordingly, the solution of the
pulley problem usually consists in finding the necessary diameter of
the driving pulley relative to that of the pulley on the generator in
order to furnish the required speed.

=Ques. What is the chief objection to belt drive?=

Ans. The large amount of floor space required.

[Illustration: FIG. 2,810.--Tandem drive for economizing floor space
with belt transmission. Belts of different lengths are used, as
shown, each of which passes over the driving wheel _d_ of the engine,
and then over the pulley wheel of one of the generators. In such
an arrangement the belts would be run lengthwise through the room
in which the machines are placed, and it is obvious that since the
width of the room would be governed by the width of the machines thus
installed, this method is a very efficient one for accomplishing the
end in view.]

=Ques. How may the amount of space that would ordinarily be required
for belt drive, be reduced?=

Ans. By driving machines in tandem as in fig. 2,810, or by the double
pulley drive as in fig. 2,811.

=Ques. What is the objection to the tandem method?=

Ans. The most economical distance between centers cannot be employed
for all machines.

=Ques. What is the objectionable tendency in resorting to floor
economy methods with belt transmission?=

Ans. The tendency to place the machines too closely together. This is
poor economy as it makes the cleaning of the machines a difficult and
dangerous task; it is therefore advisable to allow sufficient room
for this purpose regardless of the method of belting employed.

[Illustration: FIG. 2,811.--Double pulley drive for economizing floor
space with belt transmission. Where a center crank engine is used
both pulleys may be employed by belting a machine to each as shown.
Although considerable floor space would be saved by the use of this
scheme if the generators thus belted were placed at M and G yet still
more floor space would be saved by having them occupy the positions
indicated at M and S.]

=Ques. What is the approved location for an alternator exciter?=

Ans. To economize floor space the exciter may be placed between the
alternator and engine at S in fig. 2,811.

=Belts.=--In the selection of a belt, the quality of the leather
should be first under consideration. The leather must be firm, yet
pliable, free from wrinkles on the grain or hair side, and of an even
thickness throughout.

[Illustration: FIG. 2,812.--Separately excited belt driven alternator
showing approved location of exciter. In an electrical station where
alternating current is generated, the alternators for producing
the current generally require separate excitation for their field
windings; that is, it is usually necessary to install in conjunction
with an alternator a small dynamo for supplying current to the
alternator field. The exciter is a comparatively small machine; in
fact, it requires only about 1 per cent. of the capacity of the
alternator which it excites, and so being small is often belted to
an auxiliary pulley mounted on the alternator shaft. Considerable
floor space would be occupied by an installation of this nature if
the exciter be placed at M, and belted to the alternator as indicated
by the dotted lines. By locating the exciter at S, between the
alternator and the engine, much floor space will be saved and the
general appearance of the installation improved.]

If the belt be well selected and properly handled, it should do
service for twenty years, and even then if the worn part be cut off,
the remaining portion may be remade and used again as a narrower and
shorter belt.

     Besides leather belts, there are those made of rubber which
   withstand moisture much better than leather belts, and which also
   possess an excellent grip on the pulley; they are, however, more
   costly and much less durable under normal conditions.

     In addition to leather and rubber belts, there are belts
   composed of cotton, of a combination of cotton and leather, and
   of rope. The leather belt, however, is the standard and is to be
   recommended.

Equally important with the quality of a belt is its size in order to
transmit the necessary power.

     The average strain under which leather will break has been found
   by many experiments to be 3,200 pounds per square inch of cross
   section. A good quality of leather will sustain a somewhat greater
   strain. In use on the pulleys, belts should not be subjected to a
   greater strain than one eleventh their tensile strength, or about
   290 pounds to the square inch or cross section. This will be about
   55 pounds average strain for every inch in width of single belt
   three-sixteenths inch thick. The strain allowed for all widths
   of belting--single, light double, and heavy double--is in direct
   proportion to the thickness of the belt.

=Ques. How much horse power will a belt transmit?=

Ans. The capacity of a belt depends on, its width, speed, and
thickness. _A single belt one inch wide and travelling 1,000 feet per
minute will transmit one horse power; a double belt under the same
conditions, will transmit two horse power._

[Illustration: FIG. 2,813.--One horse power transmitted by belt to
illustrate the rule given above. A pulley is driven by a belt by
means of the friction between the surfaces in contact. Let T be the
tension on the driving side of the belt, and T', the tension on the
loose side; then the driving force = T-T'. In the figure T is taken
at 34 lbs. and T' at 1 lb.; hence driving force = 34-1 = 33 lbs.
Since the belt is travelling at a velocity of 1,000 feet per minute
the power transmitted = 33 lbs. × 1,000 ft. = 33,000 ft. lbs. per
minute = 1 horse power.]

     This corresponds to a working pull of 33 and 66 lbs. per inch of
   width respectively.

     =Example.=--What width double belt will be required to transmit
   50 horse power travelling at a speed of 3,000 feet per minute?

     The horse power transmitted by each inch width of double belt
   travelling at the stated speed is

                3,000
           1 ×  -----  × 2 = 6,
                1,000

hence the width of belt required to transmit 50 horse power is

           50 ÷ 6 = 8.33, say 8 inches.

=Ques. At what velocity should a belt be run?=

Ans. At from 3,000 to 5,000 feet per minute.

=Ques. How may the greatest amount of power transmitting capacity be
obtained from belts?=

Ans. By covering the pulleys with leather.

=Ques. How should belts be run?=

Ans. With the tight side underneath as in fig. 2,814.

[Illustration: FIGS. 2,814 and 2,815.--Right and wrong way to run a
belt. The tight side should be underneath so as to increase the arc
of contact and consequently the adhesion, that is to say, a _better
grip_, is in this way obtained.]

=Ques. What is a good indication of the capacity of a belt in
operation?=

Ans. Its appearance after a few days' run.

     If the side of the belt coming in contact with the pulley assume
   a mottled appearance, it is an indication that the capacity of
   the belt is considerably in excess of the power which it is
   transmitting, inasmuch as the spotted portions of the belt do not
   touch the pulley; and in consequence of this there is liable to be
   more or less slipping.

     Small quantities of a mixture of tallow and fish oil which
   have previously been melted together in the proportion of two of
   the former to one of the latter, will, if applied to the belt
   at frequent intervals, do much toward softening it, and thus
   by permitting its entire surface to come in contact with the
   pulley, prevent any tendency toward slipping. The best results
   are obtained when the smooth side of the belt is used next to the
   pulley, since tests conducted in the past prove that more power is
   thus transmitted, and that the belt lasts longer when used in this
   way.

[Illustration: FIG. 2,816.--The Hill friction clutch pulley for power
control. The clutch mechanism will start a load equivalent to the
double belt capacity of the pulley to which the clutch is attached.]

=Ques. What is the comparison between the so called endless belts and
laced belts?=

Ans. With an endless belt there is no uneven or noisy action as with
laced belts, when the laced joint passes over the pulleys, and the
former is free from the liability of breakage at the joint.

=Ques. How should a belt be placed on the pulleys?=

Ans. The belt should first be placed on the pulley at rest, and then
run on the other pulley while the latter is in motion.

     The best results are obtained, and the strain on the belt is
   less, when the speed at which the moving pulley revolves is
   comparatively low. With heavy belts, particular care should be
   taken to prevent any portion of the clothing being caught either
   by the moving belt or pulleys, as many serious accidents have
   resulted in the past from carelessness in regard to this important
   detail. The person handling the belt should, therefore, be sure of
   a firm footing, and when it is impossible to secure this, it is
   advisable to stop the engine and fit the belt around the engine
   pulley as well as possible by the aid of a rope looped around the
   belt.

[Illustration: FIG. 2,817--Sectional view of Hill clutch mechanism.
In every case the mechanism hub A, and in a clutch coupling the
ring W, is permanently and rigidly secured to the shaft and need
not be disturbed when removing the wearing parts. When erected, the
adjustment should be verified, and always with the clutch and ring
engaged and at rest. If the jaws do not press equally on the ring, or
if the pressure required on the cone be abnormal, loosen the upper
adjusting nuts T´ on eye bolts and set up the lower adjusting nuts
T´´ until each set of jaws is under the same pressure. Should the
clutch then slip when started it is evident that the jaw pressure is
insufficient and a further adjustment will be necessary. All clutches
are equipped throughout with split lock washers. Vibration or shock
will not loosen the nuts if properly set up. The jaws can be removed
parallel to the shaft as follows: Remove the gibs V, and withdraw the
jaw pins P, then pull out the levers D. Do not disturb the eye bolt
nuts T´ and T´´. The outside jaws B can now be taken out. Remove the
bolt nuts I allowing the fulcrum plates R to be taken off. On the
separable hub pattern the clamping bolts must be taken out before
fulcrum plate is removed. The inside jaws C may now be withdrawn.
Always set the clutch operating lever in the position as shown in
fig. 2,816 to avoid interference with mechanism parts. Oil the moving
parts of the clutch. Keep it clean. Examine at regular intervals.]

=Ques. Under what conditions does a belt drive give the best results?=

Ans. When the two pulleys are at the same level.

     If the belt must occupy an inclined position it should not form
   a greater angle than 45 degrees with the horizontal.

=Ques. What is a characteristic feature in the operation of belts,
and why?=

Ans. Belts in motion will always run to the highest side of a
pulley; this is due partially to the greater speed in feet per minute
developed at that point owing to the greater circumference of the
pulley, and also to the effects of centrifugal force.

     If, therefore, the highest sides of both pulleys be in line with
   each other, and the shafts of the respective pulleys be parallel
   to each other, there will be no tendency for the belt to leave
   the pulleys when once in its proper position. In order that these
   conditions be maintained, the belt should be no more than tight
   enough to prevent slipping, and the distance between the centers
   of the pulleys should be approximately 3.5 times the diameter of
   the larger one.

[Illustration: FIG. 2,818.--Hill clutch mechanism Smith type. The
friction surfaces are wood to iron, the wood shoes being made from
maple. All parts of the toggle gear are of steel and forgings with
the exception of the connection lever which is of cast iron.]

=Ques. What minor appurtenances should be provided in a station?=

Ans. Apparatus should be installed as a prevention against accidents,
such as fire, and protection of attendants from danger.

     In every electrical station there should be a pump, pipes
   and hose; the pump may be either directly connected to a small
   electric motor or belted to a countershaft, while the pipes
   and hose should be so placed that no water can accidentally
   reach the generators and electrical circuits. A number of fire
   bucket filled with water should be placed on brackets around the
   station, and with these there should be an equal number of bucket
   containing dry sand, the water being used for extinguishing fire
   occurring at a distance from the machines and conductors, and the
   sand for extinguishing fire in current carrying circuits where
   water would cause more harm than benefit. To prevent the sand
   being blown about the station, each sand bucket, when not in use,
   should be provided with a cover.

     Neat cans and boxes should be mounted in convenient places for
   greasy rags, waste, nuts, screws, etc., which are used continually
   and which therefore cannot be kept in the storeroom.

     While it is important to guard against fire in the station,
   it is equally necessary to provide for personal safety. All
   passages and dark pits should therefore be thoroughly lighted
   both day and night, and obstacles of any nature that are not
   absolutely necessary in the operation of the station, should be
   removed. Moving belts, and especially those passing through the
   floor, should be enclosed in iron railings. If high voltages be
   generated, it is well to place a railing about the switchboard to
   prevent accidental contact with current carrying circuits, and in
   such cases it is also advisable to construct an insulated platform
   on the floor in front of the switchboard.

[Illustration: FIG. 2,819.--Method of joining adjacent switchboard
panels.]

=Switchboards.=--The plan of switchboard wiring for alternating
current work depends upon the system in use and this latter may be
either of the single phase, two phase, three phase, or monocyclic
types. The general principles in all these cases, however, are
practically identical.

     Fig. 2,820 shows the switchboard wiring for a single phase
   alternator. As an aid in reading the diagram, the conductors
   carrying alternating current are represented by solid lines, and
   those carrying direct current, by dotted lines.

[Illustration: FIG. 2,820.--Switchboard wiring for a single phase
separately excited alternator. The direct current circuits are
represented by dotted lines, and the alternating current circuit, by
solid lines.]

     The exciter shown at the right is a shunt wound machine. By
   means of the exciter rheostat, the voltage for exciting the field
   winding of the alternator is varied; this, in turn, varies the
   voltage developed in the alternator since the main leads of the
   exciter are connected through a double pole switch G to the field
   winding of the alternator.

[Illustration: FIGS. 2,821 to 2,825.--General Electric diagrams of
connections. A, ammeter; C.B, circuit breaker; C.P, candle power;
C.T, current transformer; D.R, discharge resistance; F, fuse; F.S,
field switch; L, lamp; O.C, overload coil; P.P, pressure plug;
P.R, pressure receptacle; R.C, reactance; rheo, rheostat; R.P,
synchronizing plug, running; R.S, resistance; S, switch; S.I,
synchronism indicator; S.P, synchronizing plug, starting; S.R,
synchronizing receptacle; V, voltmeter.]

     A rheostat is also introduced in the alternator field winding
   circuit to adjust the alternator pressure. It may seem unnecessary
   to employ a rheostat in each of two separate field circuits to
   regulate the voltage of the alternator, but these rheostats are
   not both used to produce the same result. When a considerable
   variation of pressure is required, the exciter rheostat is
   manipulated, whereas for a fine adjustment of voltage the
   alternator rheostat is preferably employed.

     Sometimes a direct current ammeter is introduced in the
   alternator's field circuit to aid in the adjustment.

     The main circuit of alternator after being protected on both
   sides by fuses, runs to the double pole switch K. These fuses
   serve as a protection to the alternator in case of a short circuit
   at the main switch. It will be noticed the fuses are of the single
   pole type and are mounted a considerable distance apart; this is
   to prevent any liability of a short circuit between them in case
   of action. Enclosed fuses are now used entirely for such work,
   since in these there is no danger of heated metal being thrown
   about and causing damage when the fuse wire is melted. Enclosed
   fuses are also more readily and quickly replaced than open fuses,
   the containing tube of each being easy to adjust in circuit, and
   when the fuse wire within is once melted the tube is discarded for
   a new one.

     The main circuit after passing through the main switch is
   further protected on both sides by circuit breakers. Leaving these
   protective devices, the left hand side of the circuit includes
   the alternating current ammeter, and then connects with one of
   the bus bars. The right hand side of the circuit runs from the
   circuit breaker to the other bus bar. As many feeder circuits
   may be connected to the bus bars and supplied with current by
   the alternator as the capacity of this machine will permit. If,
   however, there be more than one feeder circuit, each must be wired
   through a double pole switch.

     In alternating current work the pressures dealt with are much
   greater than those in direct current installations, so that
   proportionate care must be taken in the wiring to remove all
   possibility of grounds.

     To locate such troubles, however, should they occur, a ground
   detector is provided. For this class of work the ground detector
   must be an instrument especially designed for high pressure
   circuits. Two of its terminals should be connected to the line
   wires and the third, to ground; in case of a leak on the line, a
   current will then flow through the detector and by the position of
   the pointer the location and seriousness of the leak may be judged.

     A step down transformer is also rendered necessary for the
   voltmeter and the pilot lamps, owing to the high voltage in use.
   The primary winding of the transformer is connected across the
   main circuit of the alternator. This connection should never be
   made so that it will be cut out of circuit when the main switch is
   open, for it is always advisable to consult the voltmeter before
   throwing on the load by closing this switch.

[Illustration: FIGS. 2,826 to 2,829.--General Electric diagrams of
connections. A, ammeter; C.B, circuit breaker; C.P, candle power;
C.T, current transformer; D.R, discharge resistance; F, fuse; F.S,
field switch; L, lamp; O.C, overload coil; P.P, pressure plug;
P.R, pressure receptacle; R.C, reactance; rheo, rheostat; R.P,
synchronizing plug, running; R.S, resistance; S, switch; S.I,
synchronous indicator: S.P, synchronizing plug, starting; S.R,
synchronizing receptacle: V, voltmeter.]

=Ques. How does the switchboard wiring for a two phase system differ
from the single phase arrangement shown in fig. 2,820?=

Ans. It is practically the same, except for the introduction of an
extra ammeter and a compensator in each of the outside wires, and in
the use of a four pole switch in place of the two pole main switch.

     The ammeters, of course, are for measuring the alternating
   currents in each of the two phases or legs of the system, and the
   compensators are two transformers with their primary coils in
   series with the outside wires and their secondary coils in series
   with each other across the outside wires. The transformers thus
   connected are known as compensators or pressure regulators, and
   as such compensate for the drop in pressure on either side of the
   system.

=Ques. How is the four pole main switch wired?=

Ans. Its two central terminals which connect directly with the line
wires, are joined together by a conductor, and from this point one
wire is led off. This wire, together with the two outside wires, form
the feeders of the system.

=Ques. How many voltmeters are required for the two phase system?=

Ans. One voltmeter is sufficient on the board if a proper switching
device be employed to shift its connections across either of the two
circuits; otherwise, two voltmeters will be necessary, one bridged
across each of these respective circuits.

     The same reasoning holds true in regard to ground detectors,
   so that one or two of these will be required, depending upon the
   aforementioned conditions.

=Ques. What are the essential points of difference between the single
phase switchboard wiring as shown in fig. 2,820, and that required
for a three wire three phase system?=

Ans. The three phase system requires the use of a three pole switch
in place of the two pole switch; the insertion of an ammeter, a
circuit breaker, and a compensator in each of the three wires of the
system; the presence of two ground detectors instead of one, and the
addition of a voltmeter switch if but one voltmeter be provided, or
else the installation of two voltmeters, connected the one between
the middle wire and outer right hand wire, and the other between the
middle wire and outer left hand wire.

[Illustration: FIG. 2,830.--Diagram of switchboard connections for
General Electric automatic voltage regulator with two exciters and
two alternators.]

=Ques. Mention a few points relating to lightning arresters.=

Ans. In most cases where direct current is used they are mounted
on the walls of the station near the place at which the line wires
enter. If they be mounted outside the station at this point, special
precautions should be taken to keep them free from moisture by
enclosing them in iron cases, but no matter where they are located it
is necessary that they be dry in order to work properly.

[Illustration: FIGS. 2,831 and 2,832.--Garton-Daniels alternating
current lightning arrester; diagram showing connections. A lightning
discharge takes the path indicated by the dotted line, across the
upper air gap A, through resistance rod B, C, D, across copper strip
R on the base, thence flowing to ground through the movable plunger
M, lower on gap N, and ground binding post L. The discharge path is
practically straight, contains an air gap, distance of but 3/32 inch,
a series resistance averaging but 225 ohms. The lightning discharge
does not flow through the flexible lead connecting band D on the
lower end of the resistance rod with the top of the movable plunger.
These two points are electrically connected by the heavy copper
strip R, and lightning discharges generally, if not always, take the
path across this copper strip in preference to flowing through the
inductance of the one turn of flexible cable. When a discharge occurs
from line to ground through any lightning arrester, the air gaps arc
over, and so there is offered a path from line to ground for the line
current. This flow of line current following the lightning discharge
to ground may vary anywhere from a small capacity current where
the arrester is installed on an ungrounded circuit, a moderately
heavy flow on a partially grounded circuit, to a very heavy flow on
a grounded circuit--either a circuit operated as a dead grounded
circuit, or a circuit which has become accidentally grounded during
a storm. The path taken by this flow of line current from line to
ground may be traced by following the path shown by the dashed line.
It, as seen, crosses upper air gap A, flows through section B of the
resistance rod to band C. Leaving band C it flows through the magnet
winding H, thence to band D on the resistance rod, through flexible
lead to upper end of movable plunger, through movable plunger, across
lower air gap N, to ground binding post L, thence to ground. The
function of the short length of resistance rod CD is as follows: It
has an ohmic resistance of about 30 ohms but is _non-inductive_.
Magnet winding H, connected to bands C and D on the ends of this
short length of rod has an ohmic resistance of 3 ohms, but is _highly
inductive_. Lightning discharges being of _high frequency_ take the
higher resistance _but non-inductive_ path CD in their passage from
line to ground. The flow of normal current from line to ground being
of a very low frequency, 25 or 60 cycles in ordinary alternating
current circuits, zero in direct current circuits--takes the _low
resistance_ path through coil H in its path to ground. Section CD of
the rod is used therefore simply to shunt the inductance of winding
H to high frequency lightning discharges, leaving the lightning
discharge path in the arrester a _non-inductive_ highly efficient
path. In all Garton-Daniels A. C. lightning arresters operating on
non-grounded or partially grounded circuits, the action of the air
gaps and series resistance are together sufficient to extinguish the
flow of normal current to ground at the zero point of the generator
voltage wave. If, however, as frequently happens, the line grounds
accidentally during a storm, then the arrester does not have to
depend for its proper operation on the arc extinguishing properties
of the air gaps and resistance, but the heavier flow of line current
through the arrester energizes the movable plunger, which raises
upward in the coil, opening the circuit between the discharge point M
and the lower end of the plunger. To limit the flow of line current
to ground the resistance rod B is provided, there being approximately
225 ohms between the discharge point A and clamp C in the 2,500 volt
arrester. This feature is particularly effective where the circuit is
temporarily or accidentally grounded. The series resistance prevents
a heavy short circuit through the arrester and limits the current to
a value that is readily broken by the cut out and is not enough to
impede the passage of the discharge.]


[Illustration: FIG. 2,833.--Diagram of switchboard connections for
General Electric automatic voltage regulator with three exciters and
three alternators.]

     If possible, one place should be set aside for them and a marble
   or slate panel provided on which they may be mounted.

     Wooden supports are undesirable for lightning arresters on
   account of the fire risk incurred; this, however, may be reduced
   to a minimum by employing skeleton boards and using sheets of
   asbestos between the arresters and the wood.

     In parts of the country where lightning is of common occurrence
   and where overhead circuits are installed which carry high
   pressures, heavy currents, and extend over considerable territory,
   it is advisable to have the station well equipped with lightning
   arresters of the most improved types.

     In each side of the main circuit, between the lightning arrester
   connections and the switchboard apparatus there should be
   connected a choke coil or else each of the main conductors at this
   point should be tightly coiled up part of its length to answer the
   same purpose.

     A quick and effective way of coiling up a wire consists in
   wrapping around a cylindrical piece of iron or wood that part
   of the conductor in which it is desired to have the coils, the
   desired number of times, and then withdrawing the cylindrical
   piece. The coils, each of which may contain 50 or 200 turns,
   thus inserted in the main circuit introduce a high resistance or
   reluctance to a lightning current, and thus prevent it passing
   to the generator; there will, however, be an easy path to earth
   afforded it through the lightning arrester, and so no damage will
   be done. Coils of the nature just mentioned may advantageously be
   introduced between the generator and switchboard to take up the
   reactive current developed upon the opening of the circuit, and in
   the case of suspended conductors, the coils may be used to take up
   the slack by the spring-like effect produced by them.

     The safety of the operator should be especially considered in
   the design of high pressure alternating current switchboards.

     Such protection may be secured by screening all the exposed
   terminals, or preferably by mounting all the switch mechanism on
   the back of the board with simply the switch handle projecting
   through to the front; by pushing or pulling the switch handle, the
   connections can thus be shifted either to one side of the system
   or to the other.

=Ques. Upon what does the work of assembling a switchboard depend?=

Ans. It depends almost entirely upon the size of the plant, varying
from the simple task of mounting a single panel in the case of an
isolated plant, to the more difficult problem of supporting a large
number of panels in a central station.

=Ques. When the material chosen for a switchboard must be shipped a
considerable distance, what form of board should be used?=

Ans. The board units or "slabs" should be of small dimensions, to
avoid the liability of breakage and expense of renewal when a unit
becomes cracked or machine injured.

[Illustration: FIGS. 2,834 and 2,835.--Front and rear views showing
General Electric automatic voltage regulator mounted on switchboard
panel.]

     Ordinarily, switchboards vary from five to eight feet in
   height and the widths of the panels vary from five to six feet.
   In some boards the seams between the slabs run vertically, and
   in others horizontally. In order to render the assembling of
   the switchboard as simple as possible, and its appearance when
   finished the most artistic, these seams should run horizontally
   rather than vertically. The edges of each of the slabs should also
   be chamfered so that there will be less danger of their breaking
   out when being mounted on the framework.

=Ques. In assembling a switchboard, how should the lower slabs be
placed, and why?=

Ans. They should be suspended a little distance from the floor to
prevent contact with any oil, dirt, water or rubbish that might be on
the floor.

=Ques. How are the slabs or panels supported?=

Ans. They are carried on an iron or wooden framework with braces to
give stability.

     The braces should be securely fastened at one end to the wall of
   the station, and at the other end to the framework of the board,
   as shown in fig. 2,836.

     To fasten the switchboard end of the brace directly to the
   slate, marble or other material composing the board is poor
   practice and should never be attempted.

     If the station be constructed of iron, these switchboard braces
   must be such that they will thoroughly insulate the board and its
   contents from the adjoining wall.

[Illustration: FIG. 2,836.--Method of supporting the framework of a
switchboard.]

=Ques. What is the usual equipment of a switchboard?=

Ans. It comprises switching devices, current or pressure limiting
devices, indicating devices, and fuses for protecting the apparatus
and circuits.

[Illustration: FIG. 2,837.--Diagram showing elementary connections of
General Electric automatic regulator for direct current. It consists
essentially of a main control magnet with two independent windings
and a differentially wound relay magnet. One winding, known as the
pressure winding, of the main control magnet is connected across the
dynamo terminals, the other across a shunt in one of the load mains.
The latter is the "compensating winding" and it opposes the action
of the pressure winding so that as the load increases, a higher
pressure at the dynamo is necessary to "over compound" for line drop.
In ordinary practice, the voltage terminals are connected to the bus
bars, and the compensating shunt inserted in one of the principal
feeders of the system. In operation the shunt circuit across the
dynamo field rheostat is first opened by means of a switch provided
for that purpose on the base of the regulator and the rheostat turned
to a point that will reduce the generator voltage 35 per cent below
normal. The main control magnet is at once weakened and allows the
spring to pull out the movable core until the main contacts are
closed. This closes the second circuit of the differential relay,
thus neutralizing its windings. The relay spring then lifts the
armature and closes the relay contacts. The switch in the shunt
circuit across the dynamo field rheostat is now closed, practically
short circuiting the rheostat, and the dynamo voltage at once rises.
As soon as it reaches the point for which the regulator has been
adjusted, the main control magnet is strengthened, which causes the
main contacts to open, which in turn open the relay contacts across
the rheostat. The rheostat is now in the field circuit, the voltage
at once falls off, the main contacts are closed, and relay armature
released, and shunt circuit across the rheostat again completed. The
voltage then starts to rise and this cycle of operation is continued
at a high rate of vibration, maintaining not a constant but a steady
voltage at the bus bars. When neither the compensating winding nor
pressure wires are used, there will be no "over compounding" effect
due to increase of load and a constant voltage will be maintained at
the bus bars. The compensating winding on the control magnet, which
opposes the pressure winding is connected across an adjustable shunt
in the principal feeder circuit. As the load increases the voltage
drop across the shunt increases and the effect of the compensating
winding becomes greater. This will require a higher voltage on the
pressure winding to open the main contacts and the regulator will
therefore cause the dynamo to compensate for line drop, maintaining
at the bus bars a steady voltage without fluctuations, which rises
and falls with a load on the feeders, giving a constant voltage at
the lamps or center of distribution. The compensating shunt may be
adjusted so as to compensate for any desired line drop up to 15 per
cent; it is preferably placed in the principal lighting feeder, but
may be connected to the bus bars so that the total current will pass
through it. The latter method, however, is sometimes desirable, as
large fluctuating power loads on separate feeders might disturb the
regulation of the lighting feeders. Adjustment is made by sliding
the movable contact at the center of the shunt. This contact may be
clamped at any desired point and determines the pressure across the
compensating winding of the regulator's main control magnet. Where
pressure wires are run back to the central station from the center
of distribution they may be connected directly to the pressure
winding of the main control magnet, and it is unnecessary to use the
compensating shunt. The pressure wires take the place of the leads
from the control magnet to the bus bars and maintain a constant
voltage at the center of distribution.]

     On some switchboards are also mounted small transformers for
   raising or lowering the voltages, and lightning arresters as a
   protection from lightning. In addition to the apparatus previously
   mentioned nearly all switchboards carry at or near their top two
   or more incandescent lamps provided with shades or reflectors, for
   lighting the board.

=Ques. What should be done before wiring a switchboard?=

Ans. The electrical connections between the various apparatus
mounted on the face or front of the board, are made on the back of
the board. It is necessary that these connections be properly made
else considerable electrical power will be wasted at this point. The
wiring on the back of the board should therefore be planned out on
paper before commencing the work.

[Illustration: FIG. 2,838.--Diagram showing connections of General
Electric automatic voltage regulator for direct current as connected
for maintaining balanced voltage on both sides of a three wire system
using a balancer set. In operation, should the voltage on the upper
bus bars become greater than that on the lower ones, the middle and
upper contacts on the regulator will close, thus opening the relay
contacts to the left and closing those to the right. This inserts all
the resistance in the field of balancer A, and short circuits the
resistance in the field of balancer B. A will then be running as a
motor, and B as a dynamo, thereby equalizing the two voltages until
that on the lower bus bars becomes greater than that of the upper
ones; then the regulator contacts operate in the opposite direction
and balancer A is run as a dynamo, and balancer B as a motor. This
cycle of operation is repeated at the rate of from three to four
hundred times per minute, thus maintaining a balanced voltage on the
system.]

     In laying out the plan of wiring care must be taken to allow
   sufficient contact surface at each connection; there should be not
   less than one square inch of contact surface allowed for each 160
   amperes of current transmitted.

[Illustration: FIG. 2,839.--Diagram of connections of General
Electric voltage regulators for one or more alternators using one
exciter.]

     For the bus bars, which, by the way are always of copper, one
   square inch per 1,000 amperes is the usual allowance; this is
   equal to 1,000 circular mils of cross sectional area per ampere.

     Every effort should be made to give the bus bars the greatest
   amount of radiation consistent with other conditions, in order
   that their resistances may not become excessive owing to the heat
   developed by the large currents they are forced to carry. Suppose,
   for instance, the number of amperes to be generated is such as
   to require bus bars having each a cross sectional area of one
   square inch. If the end dimensions of these bars were each 1 inch
   by 1 inch, there would be less radiating surface than if their
   dimensions were each 2 inches by ½ inch.

=Operation of Alternators.=--The operation of an alternator when run
singly differs but little from that for a dynamo.

     As to the preliminaries, the exciter must first be started.
   This is done in the same way as for any shunt dynamo. At first
   only a small current should be sent through the field winding of
   the alternator; then, if the exciter operates satisfactorily and
   the field magnetism of the operator show up well, the load may
   gradually be thrown on until the normal current is carried, the
   same method of procedure being followed as in the similar case of
   a dynamo.

[Illustration: FIGS. 2,840 and 2,841.--General Electric equalizer
regulator designed to equalize the load on two machines, and diagram
of connections.]

On loading an alternator, a noticeable drop in voltage occurs
across its terminals. This drop in voltage is caused in part by the
demagnetization of the field magnets due to the armature current,
and so depends in a measure upon the position and form of the pole
pieces as well as upon those of the teeth in the armature core. The
resistance of the armature winding also causes a drop in voltage
under an increase of load.

     Another cause which may be mentioned is the inductance of the
   armature winding, which is in turn due to the positions of the
   armature coils with respect to each other and also with respect to
   the field magnets.

[Illustration: FIG. 2,842.--Connection of General Electric equalizing
regulator for equalizing loads on an engine driven dynamo and rotary
converter running in parallel. Should the load on the dynamo become
greater than that on the rotary converter, the middle and upper
contacts on the regulator close, and thus by means of the relay
switch and control motor, cause the feeder regulator to boost the
voltage on the rotary until the loads again become equal. Should
the load on the rotary converter become greater than that on the
generator, the regulator contacts operate in the reverse direction
and the feeder regulator is caused to buck the rotary voltage.]

=Alternators in Parallel.=--When the load on a station increases
beyond that which can conveniently be carried by one alternator, it
becomes necessary to connect other alternators in parallel with it.
To properly switch in a new machine in parallel with one already in
operation and carrying load, requires a complete knowledge of the
situation on the part of the attendant, and also some experience.

     The connections for operating alternators in parallel are
   shown in fig. 2,843. In the illustration the alternator A is in
   operation and is supplying current to the bus bars. The alternator
   B is at rest. The main pole switch B' by means of which this
   machine can be connected into circuit is therefore open.

[Illustration: FIG. 2,843.--Method of synchronizing with one lamp;
_dark lamp method_. Assuming A to be in operation, B, may be brought
up to approximately the proper speed, and voltage. Then if B, be
run a little slower or faster than A, the synchronizing lamp will
glow for one moment and be dark the next. At the instant when the
pressures are equal and the machines in phase, the lamp will become
dark, but when the phases are in quadrature, the lamp will glow at
its maximum brilliancy. Since the flickering of the lamp is dependent
upon the difference in frequency, the machines should not be thrown
in parallel while this flickering exists. The nearer alternator
approaches synchronism, in adjusting its speed, the slower the
flickering, and when the flickering becomes very slow, the incoming
machine may be thrown in the moment the lamp is dark by closing the
switch. The machines are then in phase and tend to remain so, since
if one slow down, the other will drive it as a motor.]

     Now, if the load increase to such extent as to require the
   service of the second alternator B, it must be switched in
   parallel with A. In order that both machines may operate properly
   in parallel, three conditions must be satisfied before they are
   connected together, or else the one alternator will be short
   circuited through the other, and serious results will undoubtedly
   follow.

Accordingly before closing main switch B, it is necessary that

  1. The frequencies of both machines be the same;
  2. The machines must be in synchronism;
  3. The voltages must be the same.

=Ques. How are the frequencies made the same?=

Ans. By speeding up the alternator to be cut in, or change the speed
of both until frequency of both machines is the same.

[Illustration: FIG. 2,844.--Diagram of connections of General
Electric automatic voltage regulator for several alternators running
in parallel with exciters in parallel.]

=Ques. How are the alternators synchronized or brought in phase?=

Ans. The synchronism of the alternators is determined by employing
some form of synchronizer, as by the single lamp method of fig.
2,843, or the two lamp method of fig. 2,845.

=Ques. In synchronizing by the one lamp method, when should the
incoming machine be thrown in?=

Ans. It is advisable to close the switch when the machines are
approaching synchronism rather than when they are receding from it,
that is to say, the instant the lamp becomes dark.

[Illustration: FIG. 2,845.--Method of synchronizing with two lamps;
_dark lamp method_. The two synchronizing lamps are connected as
shown, and each must be designed to supply its rated candle power
at the normal voltage developed by the alternators. Now since the
alternators are both running under normal field excitation the left
hand terminals of each of them will alternately be positive and
negative in polarity, while the right hand terminals are respectively
negative and positive in polarity. If, however, the alternators be
in phase with each other, the left hand terminals of both of them
will be positive while the right hand terminals are negative, and
when the left hand terminals of both machines are negative the right
hand terminals will be positive. Hence, when the machines are in
phase there will be no difference of pressure between the left hand
terminals or between the right hand terminals of the two machines.
Hence, if the synchronizing lamps be connected as shown, both will
be dark. The instant there is a difference of phase, both lamps
will glow attaining full candle power when the difference of phase
has reached a maximum. As the alternators continue to come closer
in step, the red glow will gradually fade away until the lamps
become dark. Then the switch may be closed, thereby throwing the
two machines in parallel. If the intervals between the successive
lighting up of the lamps are of short duration it is advisable to
wait until these become longer even though the other conditions are
satisfied, because where the phases pass each other rapidly there is
a greater possibility of not bringing them together at the proper
instant. An interval of not less than five seconds should therefore
be allowed between the successive lighting up of the lamps, before
closing the switch.]

[Illustration: FIG. 2,846.--Inductor type synchroscope. This type
is especially applicable where pressure transformers are already
installed for use with other meters. As it requires only about ten
apparent watts it may be used on the same transformers with other
meters. There are three stationary coils, N, M and C, and a moving
system, comprising an iron armature, A, rigidly attached to a shaft
suitably pivoted and mounted in bearings. A pointer is also attached
to the shaft. The moving system is balanced and is not subjected
to any restraining force, such as a spring or gravity control. The
axes of the coils N and M are in the same vertical plane, but 90
degrees apart, while the axis of C is in a horizontal plane. The
coils N and M are connected in "split phase" relation through an
inductive resistance P and non-inductive resistance Q, and these two
circuits are parallel across the bus bar terminals 3 and 4 of the
synchroscope. Coil C is connected through a non-inductive resistance
across the upper machine terminals 1 and 2 of the synchroscope. =In
operation=, current in the coil C magnetizes the iron core carried
by the shaft and the two projections, marked A and "iron armature."
There is however, no tendency to rotate the shaft. If current be
passed through one of the other coils, say M, a magnetic field will
be produced parallel with its axis. This will act on the projections
of the iron armature, causing it to turn so that the positive and
negative projections assume their appropriate position in the field
of the coil M. A reversal of the direction in both coils will
obviously not affect the position of the armature, hence alternating
current of the same frequency and phase in the coils C and M cause
the same directional effect upon the armature as if direct current
were passed through the coils. If current lagging 90 degrees behind
that in the coils M and C be passed through the coil N, it will cause
no rotative effect upon the armature, because the maximum value of
the field which it produces will occur at the instant when the pole
strength of the armature is zero. The two currents in the coils M and
N produce a shifting magnetic field which rotates about the shaft as
an axis. As all currents are assumed to be of the same frequency, the
rate of rotation of this field is such that its direction corresponds
with that of the armature projections at the instant when the poles
induced in them by the current in the coil C are at maximum value,
and the field shifts through 180 degrees in the same interval as is
required for reversal of the poles. This is the essential feature of
the instrument, namely, that the armature projections take a position
in the rotating magnetic field which corresponds to the direction of
the field at the instant when the projections are magnetized to their
maximum strength by their current in the coil C. If the frequency
of the currents in the coils which produce the shifting field be
less than that in the coil which magnetized the armature, then the
armature must turn in order that it may be parallel with the field
when its poles are at maximum strength.]

=Ques. What are the objections to the one lamp method?=

Ans. The filament of the lamp may break, and cause darkness, or the
lamp may be dark with considerable voltage as it takes over 20 volts
to cause a 100 volt lamp to glow.

=Ques. What capacity of single lamp must be used?=

Ans. It must be good for twice the voltage of either machine.

[Illustration: FIG. 2,847.--Brilliant lamp method of synchronizing.
The synchronizing lamps are connected as shown, and must be of the
alternator voltage. When the voltages are equal and the machines in
phase, the difference of pressure between _a_ and a given point is
the same as that between _a'_ and the same point; this obtains for
_b_ and _b'_. Accordingly, a lamp connected across _a b'_ will burn
with the same brilliancy as across _a' b_; the same holds for the
other lamp. When the voltages are the same and the phase difference
is 180° the lamps are dark, and as the phase difference is decreased,
the lamps glow with increasing brightness until at synchronism they
glow with maximum brilliancy. Hence the incoming alternator should be
thrown in at the instant of maximum brilliancy.]

=Ques. What modification of the synchronizing methods shown in
the accompanying illustrations is necessary when high pressure
alternators are used?=

Ans. Step down transformers must be used between the alternators and
the lamps to obtain the proper working voltages for the lamps.

[Illustration: FIG. 2,848.--Synchronizing with high pressure
alternators; dark and brilliant lamp methods. In both methods the
primaries of the transformers are connected in the same way across
the terminals of the alternators as shown. In the dark lamp method,
the connections between the secondary coils of the transformers must
be made so that when each is subjected to the same conditions the
action of the one coil opposes that of the other as in the dark lamp
method; then, if the transformers be both of the same design, there
will be no voltage across the lamps when the alternators are in phase
with each other. If the ratio of each transformer is such as to give,
for example, 100 volts across its secondary terminals, then the two
incandescent lamps since they are joined together in series must
each be designed for 100 volts. One 200 volt lamp could be used in
either method in place of the two 100 volt lamps. When, therefore,
the alternators are directly opposite in phase to each other, both
the lamps will burn brightly; as the alternators come together in
phase the lamps will produce less and less light, until when the
machines are exactly in phase no light will be emitted at all, at
which instant the incoming alternator should be thrown in. It must
be evident, if the transformer secondary connections are arranged as
in the brilliant lamp method, so that they do not oppose each other,
the lamps will be at maximum brilliancy when the alternators are in
phase and dark when the phase difference is 180°, assuming of course
equalized voltage.]

=Ques. How is the voltage of an incoming machine adjusted so that it
will be the same as the one already in operation?=

Ans. By varying the field excitation with a rheostat in the
alternator field circuit.

=Ques. How may two or more alternators be started simultaneously?=

Ans. After bringing each of them up to its proper speed so as to
obtain equal frequencies, the main switches may be closed, thereby
joining their armature circuits in parallel. As yet, however, their
respective field windings have not been supplied with current, so
that no harm can result in doing this. The exciters of these machines
after being joined in parallel, should then be made to send direct
current simultaneously through the field windings of the alternators,
and from this stage on the directions previously given may be
followed in detail.

=Ques. What are the conditions when two or more alternators are
directly connected together?=

Ans. If rigidly connected together, or directly connected to the same
engine, they must necessarily run in the same manner at all times.

     When machines connected in this way are once properly adjusted
   so that they are in phase with each other, their operation in
   parallel is even a simpler task than when they are all started
   together but are not directly connected.

=Ques. When an alternator is driven by a gas engine, what provision
is sometimes made to insure successful operation in parallel?=

Ans. An amortisseur winding is provided to counteract the tendency to
"hunting."

[Illustration: FIG. 2,849.--Diagram of Lincoln Synchronizer. =In
construction=, a stationary coil F, has suspended within it a coil A,
free to move about an axis in the planes of both coils and including
a diameter of each. If an alternating current be passed through both
coils, A, will take a position with its plane parallel to F. If now
the currents in A and F be reversed with respect to each other, coil
A will take up a position 180° from its former position. Reversal
of the relative directions of currents in A and F is equivalent to
changing their phase relation by 180°, and therefore this change
of 180° in phase relation is followed by a corresponding change of
180° in their mechanical relation. Suppose now, instead of reversing
the relative direction of currents in A and F, the change in phase
relation between them be made gradually and without disturbing the
current strength in either coil. It is evident that when the phase
difference between A and F reaches 90°, the force between A and F
will become reduced to zero, and a movable system, of which A may
be made a part, is in condition to take up any position demanded
by any other force. Let a second number of this movable system
consist of coil B, which may be fastened rigidly to coil A, with its
plane 90° from that of coil A, and the axis of A passing through
diameter of B. Further, suppose a current to circulate through B,
whose difference in phase relation to that in A, is always 90°. It
is evident under these conditions that when the difference in phase
between A and F is 90°, the movable system will take up a position,
such that B is parallel to F, because the force between A and F is
zero, and the force between B and F is a maximum; similarly when the
difference in phase between B and F is 90°, A will be parallel to F.
That is, beginning with a phase difference between A and F of zero
a phase change of 90° will be followed by a mechanical change on a
movable system of 90°, and each successive change of 90° in phase
will be followed by a corresponding mechanical change of 90°. For
intermediate phase relation, it can be proved that under certain
conditions the position of equilibrium assumed by the movable element
will exactly represent the phase relations. That is, with proper
design, the mechanical angle between the plane of F and that of A
and also between the plane of F and that of B, is always equal to
the phase angle between the current flowing in F and those in A and
B respectively. =As commercially constructed= coil F consists of a
small laminated iron field magnet with a winding whose terminals
are connected with binding posts. The coils A and B are windings
practically 90° apart on a laminated iron armature pivoted between
the poles of the magnet. These two windings are joined, and a tap
from the junction is brought out through a slip ring to one of two
other binding posts. The two remaining ends are brought out through
two more slip rings, one of which is connected to the remaining
binding post, through a non-inductive resistance, and the other
to the same binding post through an inductive resistance. A light
aluminum hand attached to the armature shaft marks the position
assumed by the armature.]

=Ques. What is the action of the amortisseur winding?=

Ans. Any sudden change in the speed of the field, generates a current
in the amortisseur winding which resists the change of velocity that
caused the current.

     The appearance of an amortisseur winding is shown in the cut
   below (fig. 2,850) illustrating the field of a synchronous
   condenser equipped with amortisseur winding.

[Illustration: FIG. 2,850.--General Electric field of synchronous
condenser provided with amortisseur winding. Hunting is accompanied
by a shifting of flux across the face of the pole pieces due to the
variation in the effect of armature reaction on the main field flux
as the current varies and the angular displacement between the field
and armature poles is changed. Copper short circuited collars placed
around the pole face have currents induced in them by this shifting
flux, which have such a direction as to exert a torque tending to
oppose any change in the relative position of the field and armature.
This action is similar to that of the running torque of an induction
motor and the damping device has been still further developed until
in its best form it resembles the armature winding of a "squirrel
cage" induction motor. The pole pieces are in ducts, and low
resistance copper bars placed in them with their ends joined by means
of a continuous short circuiting ring extending around the field.
Such a device has proven very effective in damping out oscillations
started from any cause, the same winding doing duty as a damping
device and to assist the starting characteristics.]

=Ques. How are three phase alternators synchronized?=

Ans. In a manner similar to the single phase method.

     Thus the synchronizing lamps may be arranged as in fig. 2,581,
   which is simply an extension of the single phase method.

=Ques. Are three lamps necessary?=

Ans. Only to insure that the connections are properly made, after
which one lamp is all that is required.

=Ques. How is it known that the connections of fig. 2,851 are
correct?=

Ans. If, in operation, the three lamps become bright or dark
_simultaneously_, the connections are correct; if this action takes
place _successively_, the connections are wrong.

     If wrong, transpose the leads of one machine until simultaneous
   action of the lamps is secured.

[Illustration: FIG. 2,851.--Method of synchronizing three phase
alternators with, three lamps, being an extension of the single phase
method.]

=Ques. What is the disadvantage of the lamp method of synchronizing?=

Ans. Lack of sensitiveness.

=Ques. Which is the accepted lamp method, dark or brilliant?=

Ans. In the United States it is usual to make the connections for
a dark lamp at synchronism, while in England the opposite practice
obtains.

     With the dark lamp method, the breaking of a filament might
   cause the machines to be connected with a great phase difference,
   whereas, with the brilliant lamp it is difficult to determine the
   point of maximum brilliancy. This latter method, therefore may be
   called the safer.

=Ques. What may be used in place of lamps for synchronizing?=

Ans. Some form of synchroscopes, or synchronizers.

=Ques. How does the Lincoln synchronizer work?=

Ans. The construction is such that a hand moves around a dial so
that the angle between the hand and the vertical is always the phase
angle between the two sources of electric pressure to which the
synchronizer is connected.

     If the incoming alternator be running too slow, the hand
   deflects in one direction, if too fast, in the other direction.
   When the hand shows no deflection, that is, when it stands
   vertical, the machines are in phase. A complete revolution of the
   hand indicates a gain or loss of one cycle in the frequency of the
   incoming machine, as referred to the bus bars.

=Cutting Out Alternator.=--When it is desired to cut out of circuit
an alternator running in parallel with others, the method of
procedure is as follows:

  1. Reduce driving power until the load has been transferred
      to the other alternators, adjusting field rheostat to obtain
      minimum current;
  2. Open main switch;
  3. Open field switch.

=Ques. What precaution should be taken?=

Ans. _Never_ open field switch before main switch.

[Illustration: FIG. 2,852.--General Electric 500 kw., horizontal
mixed pressure Curtis turbine connected to a 500 kw. dynamo. In
a Curtis turbine it is not necessary to use the whole periphery
of the first stage for low pressure steam nozzles. A section can
be partitioned off and equipped with special expanding nozzles to
receive steam at high pressure direct from the boilers. Such nozzles
deliver their steam against the same wheel as do the low pressure
nozzles, but occupy only a small portion of its periphery. The steam
is expanded in these nozzles from high pressure all the way down
to the normal pressure of the first stage, and in such expansion
acquires a high velocity and consequently contains a great deal
of energy--much more than does an equal quantity of low pressure
steam. In consequence of this, high pressure steam is used with
a far lower water rate than is obtained with low pressure steam,
or with high pressure steam reduced to low pressure in a reducing
valve. This construction is called "mixed pressure." Its function
is the same as that of the reducing valve, that is, it makes up
for a deficiency of low pressure steam by drawing direct on the
boilers. With this construction, the full power of the turbine can be
developed with: All low-pressure steam, all high pressure steam, or,
any necessary proportion of steam of each pressure. Furthermore, the
transition from all low pressure to all high pressure, through all
the conditions intermediate between these extremes, is provided for
automatically by the turbine governor; a deficiency of low pressure
steam causes the high pressure nozzles to open automatically.]

=Ques. What is the ordinary method of cutting out an alternator?=

Ans. The main switch is usually opened without any preliminaries.

=Ques. What is the objection to this procedure?=

Ans. It suddenly throws all the load on the other alternators, and
causes "hunting."

=Ques. What forms of drive are especially desirable for running
alternators in parallel, and why?=

Ans. Water turbine or steam turbine because of the uniform torque,
thus giving uniform motion of rotation.

     With reciprocating engines, the crank effect is very variable
   during the revolution, resulting in pulsations driving the
   alternator too fast or too slow, and causing cross current between
   the alternators.

=Ques. Is a sluggish, or a too sensitive governor preferable on an
engine driving alternators in parallel?=

Ans. A sluggish governor.

=Alternators in Series.=--Alternators are seldom if ever connected
in series, for the reason that the synchronizing tendency peculiar
to these machines causes them to oppose each other and fall out of
phase when they are joined together in this way. If, however, they
be directly connected to each other, or to an engine, so that they
necessarily keep in phase at all times, and thus add their respective
voltages instead of counteracting them, series operation is possible.

            NOTE.--According to the practice of the General
          Electric Co., 2½ degrees of phase difference
          from a mean is the limit allowable in ordinary
          cases. It will, in certain cases, be possible to
          operate satisfactorily in parallel, or to run
          synchronous apparatus from machines whose angular
          variation exceeds this amount, and in other cases
          it will be easy and desirable to obtain a better
          speed control. The 2½ degree limit is intended to
          imply that the maximum departure from the mean
          position during any revolution shall not exceed
          2½ ÷ 360 of an angle corresponding to two poles
          of a machine. The angle of circumference which
          corresponds to the 2½ degree of phase variation
          can be ascertained by dividing 2½ by ½ the
          number of pole; thus, in a 20 pole machine, the
          allowable angular variation from the mean would
          be 2½ ÷ 10 = ¼ of one degree.

[Illustration: FIG. 2,853.--Diagram of connections for synchronizing
two compound wound three phase alternators. A and A' are the
armatures of the two machines, the fields of which are partly
separately excited, the amount of excitation current being controlled
by the series compounding rheostats B and B', which form a stationary
shunt. It is assumed that the alternator A is connected to the
bus bars 1, 2, and 3, by the switch 1S. If an increase make it
necessary to introduce the alternator A', it is first run up to
speed and excited to standard pressure by its exciter, and then
the double plug switch 3S is closed, connecting the primary of the
station transformer T and T' with the bus bars through the secondary
coil, so that the synchronizing lamps light up when the secondary
circuit is closed through the single pole switch 4S. The primary of
the station transformer T is thus excited through the double pole
switch 5S, connecting it with the outer terminals of the armature
A'. The two alternators will now work in opposition to each other
upon the synchronizing lamps, the transformer T being operated by
the new alternator A' through the switch 2S, and the transformer
T' being operated by the working alternator A, from the bus bars.
If the new alternator be not in step with the working alternator,
the synchronizing lamps will glow, growing brighter and dimmer
alternately with greater or lesser rapidity. In this case, the
armature speed of the new alternator must be controlled in such a
manner that the brightening and dimming will occur more and more
slowly, until the lamps cease to glow or remain extinguished for
a decided interval of time. The extinction of the light is due to
the disappearance of the secondary current, and indicates that
the alternators are in step. The switch 2S should now be thrown,
thus coupling the two machines electrically, and both of them will
continue to operate in step. The double pole equalizer switch 6S
should now be closed, connecting the two field windings in parallel
and equalizing the compounding, so that any variations of load will
affect the two alternators equally. After the alternators have been
connected in parallel, the switches 4S and 5S, may be opened leaving
the switch 3S closed, to operate the switchboard lamps K, K, as pilot
lights from the bus bars.]

=Transformers.=--These, as a whole, are simple in construction, high
in efficiency, and comparatively inexpensive. Their principles of
operation are also readily understood.

The efficiency of a transformer, that is, the ratio between full
load primary and full load secondary is greatest when the load on it
is such that the sum of the constant losses equals the sum of the
variable losses.

     In general, transformers designed for high frequencies and
   large capacities are more efficient than those designed for
   low frequencies and small capacities. As a whole, however, a
   transformer leaves but little to be desired as regards efficiency,
   a modern 60 cycle transformer of 50 kilowatts capacity or more
   possesses an efficiency of approximately 98 per cent. at full load
   and an efficiency of about 97 per cent. at half load.

=Ques. How should a transformer be selected, with respect to
efficiency?=

Ans. One should be chosen, whose parts are so proportioned that the
point of maximum efficiency occurs at that load which the transformer
usually carries in service.

     In many alternating current installations, comparatively light
   loads are carried the greater part of the time, the rated full
   load or an overload being occurrences of short durations. For such
   purposes special attention should be given to the designing or
   selecting of transformers having low core losses rather than low
   resistance losses, because the latter are then of relatively small
   importance.

=Ques. What kind of efficiency is the station manager interested in?=

Ans. The "all day efficiency."

     This expression, as commonly met with in practice, denotes
   _the percentage that the amount of energy actually used by the
   consumer is of the total energy supplied to his transformer during
   24 hours_. The formula for calculating the all day efficiency of
   a transformer is based upon the supposition that the amount of
   energy used by the consumer during 24 hours is equivalent to full
   load on his transformer during five hours and is as follows:

                  5w
         E = -------------
             24c + 5r + 5w
  where
        E = the all day efficiency of the transformer,
        w = the full load in watts on the primary,
        c = the core loss in watts,
        r = the resistance loss in watts.

[Illustration: FIG. 2,854.--Performance curves of Westinghouse air
blast 550 kw, 10,500 volt transformer, 3,000 alternations.]

=Ques. What are the usual all day efficiencies?=

Ans. The average is about 85 per cent. for those of 1 kilowatt
capacity, 92 per cent. for those of 5 kilowatts capacity, 94 per
cent. for those of 10 kilowatts capacity, and about 94.5 per cent.
for those of 15 kilowatts capacity.

=Ques. What becomes of the energy lost by a transformer?=

Ans. It reappears as heat in the windings and core.

     This heat not only increases the resistances of the windings and
   core, producing thereby a further increase of their respective
   losses, but in addition causes in time a peculiar effect on the
   iron core which is intensified by the reversals of magnetism
   constantly going on within it.

     After about two years' service, the iron apparently becomes
   fatigued or tired, and this phenomenon is called aging of the
   iron. Since the life of the transformer depends to a great extent
   upon this factor, the conditions responsible for its existence
   should as far as possible be removed. Means must therefore be
   provided in the construction to radiate the heat as quickly as it
   is generated.

=Ques. What kind of oil is used in oil cooled transformers?=

Ans. Mineral oil.

[Illustration: FIG. 2,855.--General arrangement of air blast
transformers and blowers.]

=Ques. How is it obtained?=

Ans. By fractional distillations of petroleum unmixed with any other
substances and without subsequent chemical treatment.

=Ques. What is the important requirement for transformer oil?=

Ans. It should be free from moisture, acid, alkali or sulphur
compounds.

=Ques. How may the presence of moisture be determined?=

Ans. By thrusting a red hot iron rod in the oil; if it "crackle,"
moisture is present.

=Ques. Describe the Westinghouse method of drying oil.=

Ans. It is circulated through a tank containing lime, and afterwards,
through a dry sand filter.

=Ques. What is the objection to heating the oil (raising its
temperature slightly above boiling point of water) to remove the
moisture?=

Ans. The time consumed (several days) is excessive.

[Illustration: FIG. 2,856.--Small Curtis turbine generator set as
made by the General Electric Co., in sizes from 5 kw., to 300 kw.
It can be arranged to operate either condensing or non-condensing,
and at any steam pressure above 80 lbs. for the smaller sizes and
100 lbs. for the larger. There are only two main bearings. A thrust
bearing, consisting of roller bearings and running between hardened
steel face washers located at either end of the main bearings is
provided solely for centering the rotor so as to equalize the
clearance. A centrifugal governor is provided (in the smaller sizes)
completely housed, and mounted directly on the main shaft end. It
controls a balanced poppet valve through a bell crank. In the larger
sizes (75 kw. and above) the governor is mounted on a vertical
secondary shaft geared to the main shaft and controls a cam shaft
which opens or closes a series of valves in rotation, admitting the
steam to different sections of the first stage nozzles. In this
way throttling of the steam is avoided. There is also an emergency
governor which closes the throttle valve in the event of the speed
reaching a predetermined limit. The speeds of operation range from
5,000 R.P.M. for the smallest size to 1,500 R.P.M. for the largest.
The lubrication system is enclosed and is automatic. Air leakage
where the shaft passes through the wheel casing is prevented by steam
seal.]

=Ques. What effect has moisture?=

Ans. It reduces the insulation value of the oil. .06 per cent. of
moisture has been found to reduce the dielectric strength of oil
about 50 per cent. "dry" oil will withstand a pressure of 25,000
volts between two 9½ inch knobs separated .15 inch.

=Ques. What is understood by transformer regulation?=

Ans. It is the difference between the secondary voltage at no load
and at full load, and is generally expressed as a percentage of the
secondary voltage at no load.

=Ques. What governs its value?=

Ans. The resistance and reactance of the windings.

[Illustration: FIG. 2,857.--Cut off coupling for power transmission
by line shafting. It is used to cut off a driving shaft from a driven
shaft. Its use obviates the use of a _quill_, such as is shown in
fig. 2,858.]

=Ques. How may the regulation be improved?=

Ans. By decreasing the resistances of the windings by employing
conductors of greater cross section, or decreasing their reactance by
dividing the coils into sections and closely interspersing those of
the primary between those of the secondary.

            NOTE.--_The term_ ="regulation"= as here used
          is synonymous with "drop." The _voltage drop_
          in a transformer denotes the drop of voltage
          occurring across the secondary terminals of a
          transformer with load. This drop is due to two
          causes: 1, the resistance of the windings; and
          2, the reactance or magnetic leakage of the
          windings. On non-inductive load, the reactive
          drop, being in quadrature, produces but a slight
          effect, but on inductive loads it causes the
          voltage to drop, and on _leading current loads_
          it causes the voltage to rise. As the voltage
          drop of a good transformer is very small even
          on inductive load, direct accurate measurement
          is difficult. It is best to measure the copper
          loss with short circuited secondary by means of
          a wattmeter, and at the same time the voltage
          required to drive full load current through. From
          the watts, the resistance drop can be found, and
          from this and the impedance voltage, the reactive
          drop may be calculated. From these data a simple
          vector diagram will give, near enough for all
          practical purposes, the drop for any power
          factor, or the following formula may be used
          which has been deduced from the vector diagram.
               _________________________
          D = √(W + X)^{2} + (R + P)^{2} - 100 where R
          = % resistance drop; X = % reactive drop; P = %
          power factor of load; W = % wattless factor of
                 ________
          load (√1 - P^{2}); D = % resultant secondary
          drop. For non-inductive loads where P = 100 and W
                    _____________________
          = 0, D = √X^{2} + (100 + R)^{2} - 100. In the
          case of leading currents it should be considered
          negative.

     In transformers where there is a great difference in voltage
   between the primary and secondary windings, however, this remedy
   has its limitations on account of the great amount of insulation
   which must necessarily be used between the windings, and which
   therefore causes the distances between them to become such as to
   cause considerable leakage of the lines of force.

=Ques. How does the regulation vary for different transformers, and
what should be the limit?=

Ans. Those of large capacity usually have a better regulation than
those of small capacity, but in no case should its value exceed 2 per
cent.

[Illustration: FIG. 2,858.--Quill drive. This is the proper
transmission arrangement substitute for heavy service, requiring
large pulleys, sheaves, gears, rotors, etc. It is a hollow shaft
supported by independent bearings. The main driving shaft running
through the quill is thus relieved of all transverse stresses. The
power is transmitted to the quill by means of a friction or jaw
clutch. When the clutch is thrown out the pulley or sheave stands
idle and the driving shaft revolves freely within the quill. As there
is no contact between moving parts there is no wear. Jaw clutches
should be used for drives demanding positive angular displacement.
They can only be thrown in and out of engagement when at rest. All
very large clutch pulleys, sheaves, or gears designed to run loose on
the line shaft are preferably mounted on quills. The letters A, B, C,
etc., indicate the dimensions to be specified in ordering a quill.]

=Ques. What advantages have shell type transformers over those of the
core type?=

Ans. They have a larger proportion of core surface exposed for
radiation of heat, and a shorter magnetic circuit which reduces the
tendency for a leakage of the lines of force into the air.

     Both types have advantages and disadvantages as compared with
   the other. In the shell type, there is less magnetic leakage, but
   also less surface exposed for radiation, and greater difficulty in
   providing efficient insulation between the two circuits; in the
   core type there is more surface exposed for radiation and less
   difficulty in insulating the windings, but there is also a great
   leakage of the lines of magnetic force into the outer air.

=Ques. How are the windings usually arranged?=

Ans. As a rule, there is only one primary winding but the secondary
winding is generally divided into two equal sections, the four
terminals of which are permanently wired to four connection blocks
which may be connected so as to throw the secondary sections either
in parallel or in series with each other at will.

=Ques. What is necessary for satisfactory operation of transformers
in parallel?=

Ans. They must be designed for the same pressures and capacities,
their percentages of regulation should be the same and they must have
the same polarity at a given instant.

     One may satisfy himself as to the first of these conditions by
   examining the name plates fastened to the transformers, whereon
   are stamped the values of the respective pressures and capacities
   of each.

     Although equal values of regulation is given as one of the
   conditions to be satisfied, transformers may be operated in
   parallel when their percentages of regulation are not the same.
   Ideal operation, however, can be attained only under the former
   state of affairs. Suppose, for instance, a transformer having a
   regulation of two per cent. be operated in parallel with another
   of similar size and design but having a regulation of one per
   cent. The secondary pressures of these transformers at no load
   will of course be the same, but at full load if the secondary
   pressure of the one be 98 volts, that of the other will be 99
   volts. There will, therefore, be a difference of pressure of one
   volt between them which will tend to force a current backward
   through the secondary winding of the transformer delivering 98
   volts. This reversed current, although comparatively small in
   value, lowers the efficiency of the installation by causing a
   displacement of phase and a decrease in the combined power factor
   of the transformers.

=Ques. Describe the polarity test.=

Ans. The test for polarity consists in joining together by means of a
fuse wire, a terminal of the secondary winding of each transformer,
and then with the primary windings supplied with normal voltage,
connecting temporarily the remaining terminals of the secondary
windings. The melting of the fuse wire thus connected indicates that
the secondary terminals joined together are of opposite polarities,
and that the connections must therefore be reversed, whereas if the
fuse wire do not melt, it shows that the proper terminals have been
joined and that the connections may be made permanent.

[Illustration: FIG. 2,859.--Single overhung tangential water wheel
equipped with Doble ellipsoidal buckets. The central position of the
front entering wedge or lip of the bucket is cut away in the form of
a semi-circular notch, which allows a solid circular water jet to
discharge upon the central dividing wedge of the bucket without being
split in a horizontal plane.]

     The object of this test is, obviously, not to determine the
   exact polarity of each secondary terminal, but merely to indicate
   which of them are of the same polarity.

[Illustration: FIG. 2,860.--Motor generator exciter set driven by
a Pelton-Doble tangential water wheel. The water wheel runner is
mounted on the shaft overhung and the jet is regulated by either a
hand actuated or governor controlled needle nozzle. The speed of the
water wheel is equivalent to the synchronous speed of the induction
motor, hence, the latter floats on the line, and under certain
conditions may perform the functions of an alternator by feeding into
the circuit, should the water wheel tend to operate above synchronous
speed. Should any interruption to the operation of the wheel occur,
causing a diminution of speed, the induction motor would drop back
to full load speed and take up the exciter load, resulting in no
appreciable drop of exciter voltage. The only variation of speed
possible is dependent upon the "slip" of the motor. Where two or more
exciter sets are employed in the station, an advantageous arrangement
embraces the installation of a water wheel driven motor generator set
and an exciter set, consisting of merely the direct current generator
and water wheel. The induction motor being electrically tied into
the circuit, the possibility of a runaway of the water wheel is
eliminated, since its speed can only slightly exceed the synchronous
speed of the system.]

=Motor Generators.=--In motor generator sets, either the shunt or
series wound type of motor may be employed at the power producing
end of the set, but the field of the generator is either shunt
or compound wound, depending upon whether or not it is desired
to maintain or to raise the secondary voltage near full load. In
either case a rheostat introduced in the shunt field winding of the
generator will be found very essential. Both generator and motor are
so mounted on the base that their respective commutators are at the
outer ends of the set. By this means ample space surrounds all of the
working parts, and repairs can readily be made.

Motor generators are frequently used as boosters to raise or boost
the voltage near the extremities of long distance, direct current
transmission lines. Of these, electric railway systems in which it is
desired to extend certain of the longer lines, form a typical example.

[Illustration: FIG. 2,861.--Automatically governed Pelton-Doble
tangential water wheel driving exciter dynamo. The water wheel is
mounted on one end of the shaft, while the opposite end is extended
to carry a fly wheel of suitable design to compensate for the low fly
wheel effect of the direct current armature. Two bearings support
the shaft which carries the rotating elements of the unit. A needle
nozzle actuated by a direct motion Pelton-Doble governor (designed
for operation by either oil or water pressure) maintains constant
speed.]

Owing to the great cost of changing such a system over to one
employing alternating current, or storage batteries, or of
constructing an additional power station, these solutions of the
problem are usually at variance with good judgment and the amount
of money at hand. The choice then remains between the purchase of
additional wire for feeders, the connection of a booster in the old
feeders, or the installation of both larger feeders and a booster.
Of these, it is generally found that either the second or the third
mentioned alternative meets the conditions most satisfactorily.

     A booster installed in a railway system for the purpose just
   mentioned, would have a series wound motor, and the conditions
   to which it must conform would be as follows: The motor having a
   series winding must provide for the full feeder current passing
   through both armature and field windings.

     Owing to the varying loads on a railway system, due to the
   frequent starting and stopping of cars, the feeder current varies
   between zero and some such value as 150 amperes. This fluctuation
   of current through the field winding will, in ordinary cases, vary
   the magnetization of the pole pieces from zero almost to the point
   of saturation; that is, the maximum feeder current will so nearly
   fill the magnet cores with lines of force that it would be quite
   difficult to cause more lines of magnetic force to pass through
   them.

     So long as the point of saturation is not reached, however, the
   proportion of current to field strength remains constant, and
   therefore the ratio of amperes to volts will not vary.

     The severe fluctuations of the feeder current would, if the
   motor were shunt or compound wound, cause most serious sparking
   and various other troubles, but in a series motor where the back
   ampere turns on the armature that react on the field vary in
   precisely the same proportion as the ampere turns in the field,
   there exists at all times a tendency to balance the active forces
   and produce satisfactory operation. If, however, the field magnet
   cores be very large, they cannot so quickly respond, magnetically,
   to changes in the strength of the current, and there is then
   greater liability of the armature reaction momentarily weakening
   the field and thereby producing temporary sparking.

=Ques. Are motor generators always composed of direct current sets?=

Ans. No.

=Ques. Describe conditions requiring a different combination.=

Ans. For purposes where for instance direct currents of widely
different voltages are to be obtained from an alternating current
circuit, and it is desired to install but one set, a motor generator
consisting of an alternating current motor such as an induction
motor, and a dynamo must necessarily be employed.

     In such sets, it is common to find both motor and dynamo
   armatures mounted on a common shaft, and the respective field
   frames resting on a single base, although for connection on a
   very high pressure alternating current circuit, separate armature
   shafts insulated from each other but directly connected together,
   and separate bases resting on a single foundation, are usually
   employed to afford the highest degree of insulation between the
   respective circuits of the two machines.

=Ques. What is the objection to a set composed of alternating current
motor and alternator?=

Ans. The commercial field that would be naturally covered by such a
set is better supplied by a transformer.

=Ques. Why?=

Ans. Because a transformer contains no moving parts, and is therefore
simpler in construction, cheaper in price, and less liable to get out
of order.

=Dynamotors.=--A dynamotor differs from a motor generator in that
the motor armature and the generator armature are combined into one,
thereby requiring but one field frame. Since the motor and generator
armature windings are mounted on a single core, the armature reaction
due to the one winding is neutralized by the reaction caused by the
other winding. There is, consequently, little or no tendency for
sparking to occur at the brushes, and they therefore need not be
shifted on this account for different loads.

=Ques. How is a dynamotor usually constructed?=

Ans. It is usually built with two pole pieces which are shunt wound.

=Ques. Why does the voltage developed fall off slightly under an
increase of load?=

Ans. Because a compound winding cannot be provided.

[Illustration: FIGS. 2,862 and 2,863.--Method of putting on belts
when the driver is in motion, and device used. The latter is called a
_belt slipper_, and consists, as shown in fig. 2,862, of a cone and
shield, which revolve upon the stem, B, thus yielding easily to the
pull of the belt. A staff or handle C of any convenient length can be
fastened to the socket. The mode of operation is illustrated in fig.
2,863, which is self explanatory.]

=Ques. Describe the armature construction and operation.=

Ans. It consists of two separate windings; one of which is joined to
a commutator mounted on one side of the armature for motor purposes,
and the other to the commutator on the other side of the armature for
generator purposes.

     By means of two studs of brushes pressing on the motor
   commutator, current from the service wires is fed into the winding
   connected to this commutator, and since the shunt field winding
   is also excited by the current from the service wires, there is
   developed in the generator winding on the rotating armature a
   direct voltage which is proportional to the speed of rotation of
   the armature in revolutions per second, the number of conductors
   in series which constitute the generator winding, and the total
   strength of the field in which the armature revolves. This
   pressure causes current to pass through the generator winding and
   the distributing circuit when the distributing circuit to which
   this winding is connected by means of its respective commutator,
   brushes, etc., is closed.

[Illustration: FIGS. 2,864 to 2,866.--Converter connections; fig.
2,864 double delta connection; fig. 2,865 diametrical connection;
fig. 2,866 two circuit single phase connection. For six phase
synchronous converter, two different arrangements of the connections
are generally used. One is called the _double delta_, and the other
the _diametrical_ connection. Let the armature winding of the
converter be represented by a circle as in figs. 2,864 and 2,865,
and let the six equidistant points on the circumference represent
collector rings, then the secondary of the supply transformers can
be connected to the collector rings in a _double delta_ as in fig.
2,864, or across diametrical pairs of pointer as in fig. 2,865.
In the first instance, the voltage ratio is the same as for the
three phase synchronous converter and simply consists of two delta
systems. The transformers can also be connected in double star, and
in such a case the ratio between the three phase voltage between
the terminals of each star, and the direct voltage will be the same
as for double delta, while the voltage of each transformer coil,
or voltage to neutral, is 1 ÷ √3 times as much. With the
diametrical connection, the ratio is the same as for the two ring
single phase converter, it being analogous to three such systems.
                                      _      _
Hence six phase double delta E_{1} = √3E ÷ 2√2 = .612E.
Six phase diametrical, E_{1} = E ÷ √2 = .707E. The ratio of the
virtual_voltage E_{0} between any collector ring and the neutral
point is always E_{0} = (E ÷ 2) √2 = .354E. For single phase
synchronous converters, consisting of a closed circuit armature
winding tapped at two equidistant points to the two collector rings
the virtual voltage is 1 ÷ √2 × the direct current voltage. While
such an arrangement of the single phase converter is the simplest,
requiring only two collector rings, it is undesirable, especially
for larger machines, on account of excessive heating of the armature
conductors. In fig. 2,866, which represents the armature winding of a
single phase converter, the supply circuits from two secondaries of
the step down transformers are connected to four collector rings, so
that the two circuits are in phase with each other, but each spreads
over an arc of 120 electrical degrees instead of over 180 degrees
as in the single phase circuit converter. To distinguish the two
types, it is generally called a two circuit single phase synchronous
converter. The virtual voltage E_{2} bears to the direct voltage the
same relation as in the three phase converter, that is single phase
two circuit, E_{1} = √3 ÷ 2√2 =.612E.]

=Ques. How is a dynamotor started?=

Ans. It is connected at its motor end and started in the same manner
as any shunt wound motor on a constant pressure circuit.

=Ques. What precautions should be taken in starting a dynamotor?=

Ans. The necessary precautions are, to have the poles strongly
magnetized before passing current through the motor winding on the
armature; to increase gradually the current through this winding, and
not to close the generating circuit until normal conditions regarding
speed, etc., are established in the motor circuit.

=Ques. How is the current developed in the machine regulated?=

Ans. It can be regulated by the introduction of resistance in one or
the other of the armature circuits, or by a shifting of the brushes
around the commutator.

=Ques. Are dynamotors less efficient than motor generators of a
similar type?=

Ans. No, they are more efficient.

=Ques. Why?=

Ans. Because they have only one field circuit and at least one
bearing less than a motor generator.

     A motor generator has at least three bearings, and occasionally,
   four, where the set consists of two independent machines directly
   connected together.

=Rotary Converters.=--An important modification of the dynamotor
is the rotary converter. This machine forms, as it were, a link
between alternating and direct current systems, being in general a
combination of an alternating current motor and a dynamo.

[Illustration: FIG. 2,867.--Skeleton diagram showing wiring of
alternator, exciter, transformer and converter. The cut also shows
switchboard and connections.]

It has practically become a fixture in all large electric railway
systems and in other installations where heavy direct currents of
constant pressure are required at a considerable distance from the
generating plant. In such cases a rotary converter is installed
in the sub-station, and being simpler in construction, higher in
efficiency, more economical of floor space, and lower in price than
a motor generator set consisting of an alternating current motor and
a dynamo which might be used in its place, it has almost entirely
superseded the latter machine for the class of work mentioned.

=Ques. What is the objection to the single phase rotary converter?=

Ans. It is not self-starting.

=Ques. What feature of operation is inherent in a rotary converter?=

Ans. A rotary converter is a "reversible machine."

     That is to say, if it be supplied with direct current of the
   proper voltage at its commutator end, it will run as a direct
   current motor and deliver alternating current to the collector
   rings. While this feature is sometimes taken advantage of in
   starting the converter from rest, the machine is not often used
   permanently in this way, its commercial application being usually
   the conversion of alternating currents into direct currents.

=Ques. How does a rotary converter operate when driven by direct
current?=

Ans. The same as a direct current motor, its speed of rotation
depending upon the relation existing between the strength of the
field and the direct current voltage applied.

     If the field be weak with respect to the armature magnetism
   resulting from the applied voltage, the armature will rotate at a
   high speed, increasing until the conductors on the armature cut
   the lines of force in the field so as to develop a voltage which
   will be equal to that applied.

     Again, if the field be strong with respect to the armature
   magnetism, resulting from the applied voltage, the armature will
   rotate at a low speed. If, therefore, it be desired to operate the
   converter in this manner and maintain an alternating current of
   constant frequency, the speed of rotation must be kept constant by
   supplying a constant voltage not only to the brushes pressing on
   the commutator, but also to the terminals of the field winding.

[Illustration: FIG. 2,868.--General Electric synchronous converter
with series booster. This type of converter generally consists of
an alternator with revolving field mounted on the same shaft as the
converter armature. The armature of the alternator, or booster, as it
is usually called, is stationary and connected electrically in series
between the supply circuit and the collector rings of the synchronous
converter. The booster field has the same number of pole as the
converter and is generally shunt wound. A change in the booster
voltage will correspondingly change the alternating voltage impressed
on the converter and this regulation can, of course, be made so as
to either increase or decrease the impressed voltage by means of
strengthening or weakening the booster field. The voltage variation
can be made either non-automatic or automatic, and in the latter
case, it becomes necessary to provide a motor operated rheostat
controlled by suitable relays, or the booster can be provided with
a series field. By means of a booster, it is possible to vary the
direct voltage of the converter with a constant alternating supply
voltage, and this voltage regulation is obtained without disturbance
of the power factor or wave shape of the system. Synchronous
converters are frequently installed in connection with Edison
systems, where three wire direct current is required. The three wire
feature is obtained either by providing extra collector rings and
compensator, as with ordinary direct current generators, or also by
connecting the neutral wire directly to the neutral point of the
secondary winding of step down transformers, if such be furnished.]

=Ques. How does it operate with alternating current drive?=

Ans. The same as a synchronous motor.

=Ques. What is the most troublesome part and why?=

Ans. The commutator, because of the many pieces of which it is
composed and the necessary lines along which it is constructed, its
peripheral speed must be kept within reasonable limits.

=Ques. What should be the limit of the commutator speed?=

Ans. The commutator speed, or tangential speed at the brushes should
not exceed 3,000 feet per minute.

[Illustration: FIG. 2,869.--Wiring diagram for General Electric
synchronous converter with series booster as illustrated in fig.
2,868.]

=Ques. Name another limitation necessary for satisfactory operation.=

Ans. The pressure between adjacent commutator bars should not exceed
eight or ten volts.

     If the commutator bars be made narrow in order to obtain
   the necessary number for the desired voltage with the minimum
   circumference and therefore low commutator speed, the brushes
   employed to collect the current are liable to require excessive
   width in order to provide the proper cross section and yet not
   cover more than two bars at once.

=Ques. How can the commutator speed be kept within reasonable limits,
other than by reducing the width of the commutator bars?=

Ans. By using alternating current of comparatively low frequency.

     For a rotary converter delivering 500 volt direct current, the
   proper frequency for the alternating current circuit has been
   found to be 25 cycles per second.

=Ques. When a rotary converter is operated in this usual manner on an
alternating current circuit, how can the direct current be varied?=

Ans. It may be varied (from zero to a maximum) by changing the value
of the alternating pressure supplied to the machine, or it may be
altered within a limited range by moving the brushes around the
commutator, or in a compound wound converter by changing the amount
of compounding.

     Under ordinary conditions, varying the voltage developed by
   changing the voltage at the motor end is not practical, hence
   the voltage developed can be varied only over a limited range.
   In addition to this, the voltage developed at the direct current
   end bears always a certain constant proportion to the alternating
   current voltage applied at the motor end; this is due to the same
   winding being used both for motor and generator purposes. In all
   cases the proportion is such that the alternating current voltage
   is the lower, being in the single phase and in the two phase
   converters about .707 of the direct current voltage, and in the
   three phase converter about .612 of the direct current voltage.
   It is thus seen that whatever value of direct current voltage be
   desired, the value of the applied alternating current voltage must
   be lower, requiring in consequence the installation of step down
   transformers at the sub-station for reducing the line wire voltage
   to conform to the direct current pressure required.

=Ques. What is the efficiency of a rotary converter?=

Ans. It may be said to have approximately the same efficiency as that
in the average of the same output, although in reality the converter
is a trifle more efficient on account of affording a somewhat shorter
average path for the current in the armature, reducing in consequence
the resistance loss and the armature reaction.

=Ques. May a converter be overloaded more than a dynamo of the same
output, and why?=

Ans. Yes, because there is usually less resistance loss in the
armature of the converter than in the armature of the dynamo.

[Illustration: FIG. 2,870.--Wiring diagram for three wire synchronous
converter with delta-Y connected step down transformer with the
neutral brought out. It is evident that in this case each transformer
secondary receives ⅓ of the neutral current, and if this current
be not so small, as compared with the exciting current of the
transformer, it will cause an increase in the magnetic density.]

     Thus, a two phase converter may be overloaded approximately 60
   per cent., and a three phase converter may be overloaded about 30
   per cent. above their respective outputs if operated as dynamos.

=Ques. Describe how a converter is started.=

Ans. There are several methods any one of which may be employed, the
choice in any given case depending upon which of them may best be
followed under the existing conditions.

     If it be found advisable to start the converter with direct
   current, the same connections would be made between the source of
   the direct current and the armature terminals on the commutator
   side of the converter as would be the case were a direct current
   shunt motor of considerable size to be started; this naturally
   means that a starting rheostat and a circuit breaker will be
   introduced in the armature circuit.

     The shunt field winding alone is used, and this part of the
   wiring may be made permanent if, as is usually the case, the same
   source of direct current is used normally for separate field
   excitation.

[Illustration: FIG. 2,871.--Wiring diagram of three wire synchronous
converter with distributed Y secondary. This system eliminates the
flux distortion due to the unbalanced direct current in the neutral.
Two separate interconnected windings are used for each leg of the Y.
The unbalanced neutral current flowing in this system may be compared
in action to the effect of a magnetizing current in a transformer.
The effect of the main transformer currents in the primary and
secondary is balanced with regard to the flux in the transformer
core, which depends upon the magnetic current. When a direct current
is passed through the transformer, unless the fluxes produced by
the same neutralize one another, its effect on the transformer iron
varies as the magnetizing current. For example, assume a transformer
having a normal ampere capacity of 100 and, approximately, 6 amperes
magnetizing current, and assume that three such transformers are
used with Y connected secondaries for operating a synchronous
converter connected to a three wire Edison system. Allowing 25 per
cent. unbalancing, the current will divide equally among the three
legs giving 8.33 amperes per leg, which is more than the normal
magnetizing current. The loss due to this current is, however,
inappreciable, but the increased core losses may be considerable.
If a distributed winding be used, the direct current flows in the
opposite direction, around the halves of each core thus entirely
neutralizing the flux distortion. Whether the straight Y connection
is to be used is merely a question of balancing the increased core
loss of the straight Y connection against the increased copper loss
and the greater cost of the interconnected Y system. The straight
Y connection is much simpler, and it would be quite permissible to
use it for transformers of small capacities where the direct current
circulating in the neutral is less than 30 per cent. of the rated
transformer current.]

     The direct current may be derived from a storage battery, from a
   separate converter, or from a motor generator set installed in the
   sub-station for the purpose.

     An adjustable rheostat will, of course, be connected in the
   field circuit for regulation. Before starting the converter,
   however, it is necessary to do certain wiring between the
   terminals on the collector side of the machine and the alternating
   current supply wires, in order that the change over from direct
   current motive power to alternating current motive power may be
   made when the proper phase relations are established between
   the alternating current in the supply wires and the alternating
   current in the armature winding of the converter.

     In order that proper phase relations exist, the armature
   of the converter must rotate at such a speed that each coil
   thereon passes its proper reversal point at the same time as the
   alternating current reverses in the supply wires. This speed may
   be calculated by doubling the frequency of the supply current and
   then dividing by the number of pole pieces on the converter, but a
   far more accurate method of judging when the converter is in step
   or in synchronism with the supply current consists in employing
   incandescent lamps as shown in fig. 2,872.

=Ques. How is a polyphase converter started with alternating current?=

Ans. This may be done by applying the alternating pressure directly
to the collector rings while the armature is at rest. There need
be no field excitation; in fact the field windings on the separate
pole pieces should be disconnected from each other before the
alternating voltage is applied to the armature, else a high voltage
will be induced in the field windings which may prove injurious to
their insulation. The passage of the alternating current through the
armature winding produces a magnetic field that rotates about the
armature core, and induces in the pole pieces eddy currents, which,
reacting on the armature, exert a sufficient torque to start the
converter from rest and cause it to speed up to synchronism.

=Ques. How much alternating current is required to start a polyphase
converter?=

Ans. About 100 per cent. more than that required for full load.

=Ques. How may this starting current be reduced?=

Ans. Transformers may be switched into circuit temporarily to reduce
the line wire voltage until the speed become normal.

[Illustration: FIG. 2,872.--Wiring diagram showing arrangement of
incandescent lamps for determining the proper phase relations in
starting a rotary converter. The alternating current side of a
three phase converter is shown at C. The three brushes, D, T and G
pressing on its collector rings are joined in order to the three
single pole switches H, L and B which can be made to connect with
the respective wires M, R, and V, of the alternating current supply
circuit. Across one of the outside switches, H, for example, a number
of incandescent lamps are joined in series as indicated at E, while
the three pole switch (not shown) in the main circuit, between the
alternator and the single pole switches is open. If then the main
switch just mentioned and the middle switch L be both closed, and
the armature of the alternator be brought up to normal speed by
running it as a direct current motor, the lamps at E will light up
and darken in rapid succession; the lighting and darkening of the
lamps will continue until, by a proper adjustment of the speed,
the correct phase relations be established between the alternating
current in the supply circuit and the alternating current developed
in the armature of the converter. As this condition is approached,
the intervals between the successive lighting up and darkening of
the lamps will increase until they remain perfectly dark. There is
then no difference of pressure between the supply circuit M R V and
the rotary converter armature circuit, so the source of the direct
current may at that instant be disconnected from the machine, and the
switches H and B, closed. If the change over has been accomplished
before the phase relations of the two circuits differed, the
converter will at once conform itself to the supply circuit and run
thereon as a synchronous motor without further trouble. The opening
of the direct current circuit and the closing of the alternating
current supply circuit may be done by hand, but preferably by
employing a device that will automatically trip the circuit breaker
in the direct current circuit at the instant the switches in the
alternating current circuit are closed.]

     In conjunction with this method, the method of synchronizing
   shown in fig. 2,872 may be used, thus, in starting, there is
   an alternating current between the brushes which pulsates very
   rapidly, but when synchronism is approached, the pulsations
   become less rapid until finally with the converter in step with
   the alternator the pulsations entirely disappear.

     The light given by the lamps thus connected indicates accurately
   the condition of affairs at any one time, varying from a rapidly
   fluctuating light at the beginning to one of constant brilliancy
   at synchronism.

[Illustration: FIG. 2,873.--Diagram of motor converter. This machine
which is only to be used for converting from alternating to direct
current, consists of an ordinary induction motor with phase wound
armature, and a dynamo. The revolving parts of both machines are
mounted on the same shaft and from the figure it is seen that the
armature of the motor and the armature of the dynamo are also
electrically connected. The motor converter is a synchronous machine,
but the dynamo receives the current from the armature of the motor at
a frequency much reduced from that impressed upon the field winding
of the motor. Assuming that the motor and the converter have the same
number of pole, the motor will rotate at a speed corresponding to
one-half the frequency of the supply circuit. The motor will operate
half as a motor and half as a transformer, and the converter, half
as a dynamo and half as a synchronous converter, in that one-half of
the electrical energy supplied to the motor will be converted into
mechanical power for driving the converter, while the other one-half
is transferred to the secondary motor windings and thereby to the
converter armature in the form of electrical power. The capacity of
the motor is theoretically only half what it would be if it were to
convert the whole of the electrical energy into mechanical power
because the rating depends upon the speed of the rotating field and
not on that of the rotor. If the two machines have a different number
of pole, or are connected to run at different speeds, the division of
power is at a different but constant ratio. The machine starts up as
an ordinary polyphase induction motor and the field of the converter
is built up as though it were an ordinary dynamo. Motor converters
are occasionally used on high frequency systems, as their commutating
component is of half frequency, and thus permits better commutator
design than a high frequency converter. The advantage of this type
of machine is that for phase control it requires no extra reactive
coils, the motor itself having sufficient reactance. It is, however,
larger than standard converters, but smaller than motor generators,
as half the power is converted in each machine. Its efficiency is
less than for synchronous converters, and the danger of reaching
double speed in case of a short circuit on the direct current side
is very great. It has been used abroad to some extent for 60 cycle
work, in preference to synchronous converters, but with the present
reliable design of 60 cycle converters, and the general use of 25
cycles, where severe service conditions are met, as in railroading,
motor converters should not be recommended.]

=Ques. If the armature of the starting motor have a starting
resistance, how must this be connected?=

Ans. It should be connected in series with the armature inductors
before the alternating voltage is applied.

     As the motor increases in speed, the starting resistance is
   gradually short circuited until it is entirely cut out of circuit.

[Illustration: FIG. 2,874.--Sectional view of General Electric
vertical synchronous converter. In this construction, the field frame
carrying the poles is mounted on cast iron pedestals and is split
vertically. This allows the two halves of the frame to be separated
for inspection or repairs of the armature. The armature, including
commutator and collector rings, is mounted on a vertical stationary
shaft, which is rigidly supported from the foundation. The thrust
of the armature is carried on a roller bearing attached to the top
of the shaft and upper side of the armature spider. The under side
of the lower plate of the roller bearing is made spherical and fits
into a corresponding spherical cup on the end of the shaft, making
the bearing self aligning. The armature spider has a babbitted sleeve
along the fit of the vertical shaft, which acts as a guide bearing
and has to take only the thrust due to the unbalancing effect of
the rotating parts. A circulating pump furnishes oil to the roller
bearing, the oil draining off through the guide bearing. A marked
advantage of this type of construction is the accessibility of the
commutator for adjustment of the brushes, etc., as there is no pit or
pedestal bearing to interfere.]

            NOTE.--Some converters are provided
          with a small induction motor for starting
          mounted on an iron bracket cast in the converter
          frame, and whose shaft is keyed to that of the
          converter. Allowing for a certain amount of
          slip in the induction motor, the field of this
          machine must possess a less number of magnet
          poles than the converter in order to enable the
          latter machine to be brought to full synchronism.
          To start the induction motor, it is simply
          necessary to apply to its field terminals the
          proper alternating voltage. The bracket, and
          therefore the motor, is usually mounted outside
          the armature bearing on the collector side of the
          converter.

[Illustration: FIG. 2,875.--Resistance measurement by "drop" method.
The circuit whose resistance is to be measured, is connected in
series with an ammeter and an adjustable resistance to vary the
flow of current. A voltmeter is connected directly across the
terminals of the resistance to be measured, as shown in the figure.
According to Ohm's law I = E ÷ R, from which, R = E ÷ I. If then the
current flowing in the circuit through the unknown resistance be
measured, and also the drop or difference of pressure, the resistance
can be calculated by above formula. In order to secure accurate
determination of the resistance such value of current must be used
as will give large deflections of the needle on the instruments
employed. A number of independent readings should be taken with some
variation of the current and necessarily a corresponding variation
in voltage. The resistance should then be figured from each set
of readings and the average of all readings taken for the correct
resistance. Great care must be taken, however, in the readings, and
the instruments must be fairly accurate. For example, suppose that
the combined instrument error and the error of the reading in the
voltmeter should be 1 per cent., the reading being high, while the
corresponding error of the ammeter is 1 per cent. low. This would
cause an error of approximately 2 per cent. in the reading of the
resistance. In making careful measurements of the resistance, it is
also necessary to determine the temperature of the resistance being
measured, as the resistance of copper increases approximately .4
of 1 per cent. for each degree rise in temperature. Use is made of
this fact for determining the increase in temperature of a piece of
apparatus when operating under load. The resistance of the apparatus
at some known temperature is measured, this being called the cold
resistance of the apparatus. At the end of the temperature test the
hot resistance is taken. Assume the resistance has increased by 15
per cent. This would indicate a rise in temperature of 37½ degrees
above the original or cold temperature of the apparatus. Suppose then
that in measuring the cold resistance, results are obtained which are
2 per cent. low, and that in measuring the hot resistance, there be
2 per cent. error in the opposite direction. This would mean that a
total error of 4 per cent. had been made in the difference between
the hot and cold resistances, or an error of 10 degrees. The correct
rise in temperature is, therefore, about 27½ instead of 37½ degrees.
In other words, an error of 2 per cent. in measuring each resistance
has caused an error of approximately 36½ per cent. in the measurement
of the rise in temperature. The constant .4 which has been used above
is only approximate and should not be used for exact work. For detail
instructions of making calculations of resistance and temperature,
see "Standardization Rules of the A.I.E.E."]

=Ques. Describe the usual wiring for the installation of a rotary
converter in a sub-station.=

Ans. Commencing at the entrance of the high pressure cables, first
there is the wiring for the lightning arresters, then for the
connection in circuit of the high tension switching devices, from
which the conductors are led to bus bars, and thence to the step down
transformers.

[Illustration: Figs. 2,876 to 2,879.--How to connect instruments
for power measurement. There are several ways of connecting an
ammeter, voltmeter and wattmeter in the circuit for the measurement
of power. A few of the methods are discussed below. With some of the
connections it is necessary to correct the readings of the wattmeter
for the losses in the coil, or coils, of the wattmeter, or for losses
in ammeter or voltmeter. This is necessary since the instruments may
be so connected that the wattmeter not only measures the load but
includes in its indications some of the instrument losses. If the
load measured be small, or considerable accuracy is required, these
instrument losses may be calculated as follows: Loss in pressure
coils is E^{2} ÷ R, in which E is the voltage at the terminals of
the pressure coil and R is the resistance. Loss in current coil is
I^{2} R in which I is the current flowing and R the resistance of the
current coil. In general let E_{v} = voltage across terminals of the
voltmeter; E_{_w_} = voltage across the terminals of the pressure
coil of the wattmeter; I_{_w_} = current through current coil of
wattmeter; I_{_a_} = current through current coil of ammeter; R_{_v_}
= resistance of pressure coil of voltmeter; R_{_w_} = resistance of
pressure coil of wattmeter; R^{1}_{w} = resistance of current coil
of wattmeter; R_{_a_} = resistance of current coil of ammeter. Then
the losses in the various coils will be as follows: E^{2}_{_v_} ÷
R_{_v_} = loss in pressure coil of voltmeter. E^{2}_{_w_} ÷ R_{_w_}
= loss in pressure coil of wattmeter. I^{2}_{_w_} ÷ R_{_v_} = loss
in current coil of wattmeter. I^{2}_{_a_}R_{_a_} = loss in current
coil of ammeter. If connection be made as in fig. 2,876, the correct
power of the circuit will be the wattmeter reading W-(E^{2}_{_v_} ÷
R_{_v_} + E^{2}_{_w_} ÷ R_{_w_}) in which E_{_v_} = E_{_w_}. In fig.
2,877, the power is W-E^{2}_{_w_} ÷ R_{_w_}. In fig. 2,878, the power
is W-I^{2}_{_w_}R^{1}_{_w_}, or the correct power is the wattmeter
reading minus the loss in the current coil of the wattmeter. In fig.
2,879, the power is W-(E^{2}_{_w_} ÷ R_{_w_} + I^{2}_{_a_}R_{_a_})·
The usual method of connection is either as in fig. 2,876 or fig.
2,877. In either case the current reading is that of the load plus
the currents in the pressure coils of the voltmeter and wattmeter.
Unless the current being measured, however, is very small, or extreme
accuracy is desired, it is unnecessary to correct ammeter readings.
In fig. 2,877 a small error is introduced due to the fact that the
actual voltage applied to the load is that given by the voltmeter
minus the small drop in voltage through the current coil of the
wattmeter. If an accurate measure of the current in connection with
the power consumed by the load be required, the connections shown
in fig. 2,879 are used, and if extreme accuracy is required, the
wattmeter reading is reduced by the losses in the ammeter and in
the pressure coil of the wattmeter. The loss in the pressure coil
of a wattmeter or voltmeter may be as high as 12 or 15 watts at 220
volts. The loss in the current coil of a wattmeter with 10 amperes
flowing may be 6 or 8 watts. It can be easily seen that if the core
or copper losses of small transformers are being measured, it is
quite necessary to correct the wattmeter readings, for the instrument
losses. In measuring the losses of a 25 or 50 H.P. induction motor,
the instrument losses may be neglected. A careful study of the above
will show when it becomes necessary to correct for instrument losses
and the method of making these corrections. Connections are seldom
used which make it necessary to correct for the losses in the current
coils of either ammeter or wattmeter, as the losses vary with the
change in the current. On the other hand, the voltages generally
used are fairly constant at 110 or 220, and when the losses of the
pressure coils at these voltages have once been calculated, the
necessary instrument correction can be readily made.]

     On a three phase system the transformers should be joined in
   delta connection, as a considerable advantage is thereby gained
   over the star connection, in that should one of the transformers
   become defective, the remaining two will carry the load without
   change except more or less additional heating. Between the
   transformers and rotary converter the circuits should be as short
   and simple as possible, switches, fuses, and other instruments
   being entirely excluded. The direct current from the converter is
   led to the direct current switchboard, and from there distributed
   to the feeder circuits.

    =WATTMETER ERROR FOR A LOAD OF 1,000 VOLT-AMPERES=
      (For a lag of 1 degree in the pressure coil)

  +------------+----------+-------+-------------------+
  |            |          |       |Error of indication|
  |Power factor|True watts| Error |    in per cent    |
  |            |          |       |   of true value   |
  +------------+----------+-------+-------------------+
  |   1.       |  1,000   |   .3  |      0.03         |
  |    .9      |    900   |  7.6  |      0.85         |
  |    .8      |    800   | 10.5  |      1.31         |
  |    .7      |    700   | 12.5  |      1.78         |
  |    .6      |    600   | 13.9  |      2.32         |
  |    .5      |    500   | 15.1  |      3.02         |
  |    .4      |    400   | 15.9  |      3.98         |
  |    .3      |    300   | 16.6  |      5.54         |
  |    .2      |    200   | 17.1  |      8.55         |
  |    .1      |    100   | 17.3  |     17.30         |
  +------------+----------+-------+-------------------+

            NOTE.--In the iron vane type instrument when
          used as a wattmeter, the current of the series
          coil always remains in perfect phase with
          the current of the circuit, provided series
          transformers are not introduced. The error,
          then, is entirely due to the lag of the current
          in the pressure coil, and this error in high
          power factor is exceedingly small, increasing as
          the power factor decreases. In the above table
          it should be noted that the value of the error
          as distinguished from the per cent. of error,
          instead of indefinitely increasing as the power
          factor diminishes, rapidly attains a maximum
          value which is less than 2 per cent. of the power
          delivered under the same current and without
          inductance. It should also be noted that the
          above tabulation is on the assumption of a lag of
          1 degree in the pressure coil. The actual lag in
          Wagner instruments for instance, is approximately
          .085 of a degree, and the error due to the lag
          of the pressure coil in Wagner instruments is,
          therefore, proportionally reduced from the
          figures shown in the above tabulation.

=Ques. In large sub-stations containing several rotary converters how
are they operated?=

Ans. Frequently they are installed to receive their respective
currents from the same set of bus bars; that is, they may be operated
as alternating current motors in parallel. They are also frequently
operated independently from single bus bars, but very seldom in
series with each other.

[Illustration: FIG. 2,880.--Single phase motor test. In this method
of measuring the input of a single phase motor of any type, the
ammeter, voltmeter and wattmeter are connected as shown in the
illustration. The ammeter measures the current flowing through the
motor, the voltmeter, the pressure across the terminals of the motor,
and the wattmeter the total power which flows through the motor
circuit. With the connections as shown, the wattmeter would also
measure the slight losses in the voltmeter and the pressure coil of
the wattmeter, but for motors of ¼ H.P. and larger, this loss is so
small that it may be neglected. The power factor may be calculated by
dividing the true watts as indicated by the wattmeter, by the product
of the volts and amperes.]

=Ques. How may the direct current circuit be connected?=

Ans. In parallel.

            NOTE.--In motor testing, by the methods
          illustrated in the accompanying cuts, it is
          assumed that the motor is loaded in the ordinary
          way by belting or direct connecting the motor
          to some form of load, and that the object is to
          determine whether the motor is over or under
          loaded, and approximately what per cent. of full
          load it is carrying. All commercial motors have
          name plates, giving the rating of the motor and
          the full load current in amperes. Hence the
          per cent. of load carried can be determined
          approximately by measuring the current input
          and the voltage. If an efficiency test of the
          apparatus be required, it becomes necessary to
          use some form of absorption by dynamometer, such
          as a Prony or other form of brake. The output of
          the motor can then be determined from the brake
          readings. The scope of the present treatment
          is, however, too limited to go into the subject
          of different methods of measuring the output of
          the apparatus, and is confined rather to methods
          of measuring current input, voltage, and watts.
          The accuracy of all tests is obviously dependent
          upon the accuracy of the instruments employed.
          Before accepting the result obtained by any test,
          especially under light or no load, correction
          should be made for wattmeter error. See table of
          wattmeter error on page 2,075.

[Illustration: FIG. 2,881.--Three phase motor test; voltmeter and
ammeter method. If it be desired to determine the approximate load
on a three phase motor, this may be done by means of the connections
as shown in the figure, and the current through one of the three
lines and the voltage across the phase measured. If the voltage be
approximately the rated voltage of the motor and the amperes the
rated current of the motor (as noted on the name plate) it may be
assumed that the motor is carrying approximately full load. If, on
the other hand, the amperes show much in excess of full load rating,
the motor is carrying an overload. The heat generated in the copper
varies as the square of the current. That generated in the iron
varies anywhere from the 1.6 power, to the square. This method is
very convenient if a wattmeter be not available, although, it is, of
course, of no value for the determination of the efficiency or power
factor of the apparatus. This method gives fairly accurate results,
providing the load on the three phases of the motor be fairly well
balanced. If there be much difference, however, in the voltage of
the three phases, the ammeter should be switched from one circuit to
another, and the current measured in each phase. If the motor be very
lightly loaded and the voltage of the different phases vary by 2 or 3
per cent., the current in the three legs of the circuit will vary 20
to 30 per cent.]

=Ques. What provision should be made against interruption of service
in sub-stations?=

Ans. There should be one reserve rotary converter to every three or
four converters actually required.

=Ques. Why does a rotary converter operate with greater efficiency,
and require less attention than does a dynamo of the same output?=

Ans. There is less friction, and less armature resistance, the
latter because the alternating current at certain portions of each
revolution passes directly to the commutator bars without traversing
the entire armature winding as it does in a dynamo; there is no
distortion of the field and consequently no sparking, or shifting of
the brushes, since the armature reaction resulting from the current
fed into the machine and that due to the current generated in the
armature completely neutralizes each other.

[Illustration: FIG. 2,882.--Three phase motor test by the two
wattmeter method. If an accurate test of a three phase motor be
required, it is necessary to use the method here indicated. Assume
the motor to be loaded with a brake so that its output can be
determined. This method gives correct results even with considerable
unbalancing in the voltages of the three phases. With the connections
as shown, the sum of the two wattmeter readings gives the total power
in the circuit. Neither meter by itself measures the power in any
one of the three phases. In fact, with light load one of the meters
will probably give a negative reading, and it will then be necessary
to either reverse its current or pressure leads in order that the
deflection may be noted. In such cases the algebraic sums of the two
readings must be taken. In, other words, if one read plus 500 watts
and the other, minus 300 watts, the total power in the circuit will
be 500 minus 300, or 200 watts. As the load comes on, the readings of
the instrument which gave the negative deflection will decrease until
the reading drops to zero, and it will then be necessary to again
reverse the pressure leads on this wattmeter. Thereafter the readings
of both instruments will be positive, and the numerical sum of the
two should be taken as the measurement of the load. If one set of the
instruments be removed from the circuit, the reading of the remaining
wattmeter will have no meaning. As stated above, it will not indicate
the power under these conditions in any one phase of the circuit. The
power factor is obtained by dividing the actual watts input by the
product of the average of the voltmeter readings × the average of the
ampere readings × 1.73.]

=What electrical difficulty is experienced with a rotary converter?=

Ans. Regulation of the direct current voltage.

=Ques. How is this done?=

Ans. It can be maintained constant only by preserving uniform
conditions of inductance in the alternating current circuit, and
uniform conditions in the alternator.

     While changes in either of these may be compensated to a certain
   extent by adjustment of the field strength of the converter, they
   cannot be entirely neutralized in this manner; it is therefore
   necessary that both the line circuit and the alternator be
   given attention if the best results are to be obtained from the
   converter.

=Ques. What mechanical difficulty is experienced with rotary
converters?=

Ans. Hunting.

=Ques. What is the cause of this?=

Ans. It is due to a variation in frequency.

     The inertia of the converter armature tends to maintain a
   constant speed; variations in the frequency of the supply circuit
   will cause a displacement of phase between the current in the
   armature and that in the line wires, which displacement, however,
   the synchronizing current strives to decrease. The synchronizing
   current, although beneficial in remedying the trouble after it
   occurs, exerts but little effort in preventing it, and many
   attempts have been made to devise a plan to eliminate this trouble.

            NOTE.--Three phase motor test; polyphase
          wattmeter method. This is identical with the test
          of fig. 2,882, except that the wattmeter itself
          combines the movement of the two wattmeters.
          Otherwise the method of making the measurements
          is identical. If the power factor be known to be
          less than 50 per cent., connect one movement so
          as to give a positive deflection; then disconnect
          movement one and connect movement two so as to
          give a positive deflection. Then reverse either
          the pressure or current leads of the movement,
          giving the smaller deflection, leaving the
          remaining movement with the original connections.
          The readings now obtained will be the correct
          total watts delivered to the motor. If the power
          factor be known to be over 50 per cent., the same
          methods should be employed, except that both
          movements should be independently connected to
          give positive readings. An unloaded induction
          motor has a power factor of less than 50 per
          cent., and may, therefore, be used as above
          for determining the correct connections. For a
          better understanding of the reasons for the above
          method of procedure, the explanation of the two
          wattmeter method, fig. 2,882, should be read. The
          power factor may be calculated as explained under
          fig. 2,882. Connect as shown in fig 2,882. The
          following check on connection may be made. Let
          the polyphase induction motor run idle, that is,
          with no load. The motor will then operate with a
          power factor less than 50 per cent. The polyphase
          meter should give a positive indication, but
          if each movement be tried separately one will
          be found to give a negative reading, the other
          movement will give a positive reading. This can
          be done by disconnecting one of the pressure
          leads from the binding post of one movement. When
          the power factor is above 50 per cent. then both
          movements will give positive deflection.

=Ques. What are the methods employed to prevent hunting?=

Ans. 1, the employment of a strongly magnetized field relative to
that developed by the armature; 2, a heavy flywheel effect in the
converter; 3, the increasing of the inductance of the armature by
sinking the windings thereon in deep slots in the core, the slots
being provided with extended heads; and 4, the employment of damping
devices or amortisseur winding on the pole pieces of the converter.

[Illustration: FIG. 2,883.--Three phase motor test; one wattmeter
method. This method is equivalent to the two wattmeter method with
the following difference. A single voltmeter (as shown above) with
a switch, A, can be used to connect the voltmeter across either one
of the two phases. Three switches, B, C and D, are employed for
changing the connection of the ammeter and wattmeter in either one
of the two lines. With the switches B and D in the position shown,
the ammeter and wattmeter series coils are connected in the left hand
line. The switch C must be closed under these conditions in order to
have the middle line closed. Another reading should then be taken
before any change of load has occurred, with switch A thrown to the
right, switch B closed, switch D thrown to the right and switch C
opened. The ammeter and the current coil of the wattmeter will then
be connected to the middle line of the motor. In order to prevent
any interruption of the circuit, the switches B, D and C should be
operated in the order given above. With very light load on the motor
the wattmeter will probably give a negative deflection in one phase
or the other, and it will be necessary to reverse its connections
before taking the readings. For this purpose a double pole, double
throw switch is sometimes inserted in the circuit of the pressure
coil of the wattmeter so that the indications can be reversed
without disturbing any of the connections. It is suggested, before
undertaking this test, that the instructions for test by the two
wattmeter and by the polyphase wattmeter methods be read.]

=Ques. What method is the best?=

Ans. The damping method.

     The devices employed for the purpose are usually copper shields
   placed between or around the pole pieces, although in some
   converters the copper is embedded in the poles, and in others it
   is made simply to surround a portion of the pole tips.

     In any case its action is as follows: The armature rotating at a
   variable speed has a field developed therein which is assumed to
   be also rotating at a variable speed; the magnetism of this rotary
   field induces currents in the copper which, however, react on the
   armature and oppose any tendency toward a further shifting of the
   magnetism in the armature and therefore prevent the development
   of additional currents in the copper. Since copper is of low
   resistance, the induced currents are sufficient in strength to
   thus dampen any tendency toward phase displacement, and so exert a
   steadying influence upon the installation as a whole.

[Illustration: FIG. 2,884.--Three phase motor, one wattmeter and Y
box method. This method is of service, only, provided the voltages of
the three phases are the same. A slight variation of the voltage of
the different phases may cause a very large error in the readings of
the wattmeter, and inasmuch as the voltage of all commercial three
phase circuits is more or less unbalanced, this method is not to be
recommended for motor testing. With balanced voltage in all three
phases, the power is that indicated by the wattmeter, multiplied by
three. Power factor may be calculated as before.]

=Electrical Measuring Instruments.=--In the manufacture of most
measuring instruments, the graduations of the scale are made at the
factory, by comparing the deflections of the pointer with voltages
as measured on standard apparatus. The voltmeters in most common
use have capacities of 5, 15, 75, 150, 300, 500 and 750 volts each,
although in the measurement of very low resistances such as those of
armatures, heavy cables, or bus bars, voltmeters having capacities as
low as .02 volt are employed.

[Illustration: FIG. 2,885.--Test of three phase motor with neutral
brought out; single wattmeter method. Some star connected motors
have the connection brought out from the neutral of the winding. In
this case the circuit may be connected, as here shown. The voltmeter
now measures voltage between the neutral and one of the lines, and
the wattmeter the power in one of the three phases of the motor.
Therefore, the total power taken by the motor will be three times the
wattmeter readings. By this method, just as accurate results can be
obtained as with the two wattmeter method. The power factor will be
the indicated watts divided by the product of the indicated amperes
and volts.]

The difference between the design of direct current voltmeters of
different capacities lies simply in the high resistance joined in
series with the fine wire coil. This resistance is usually about 100
ohms per volt capacity of the meter, and is composed of fine silk
covered copper wire wound non-inductively on a wooden spool.

In the operation of an instrument, if the pointer when deflected do
not readily come to a position of rest owing to friction in the
moving parts, it may be aided in this respect by gently tapping
the case of the instrument with the hand; this will often enable
the obstruction, if not of a serious nature, to be overcome and an
accurate reading to be obtained.

[Illustration: FIG. 2,886.--Temperature test of a large three
phase induction motor. Temperature tests are usually made on small
induction motors by belting the motor to a generator and loading the
generator with a lamp bank or resistance until the motor input is
equal to the full load. If, however, the motor be of considerable
size, such that the cost of power becomes a considerable item in
the cost of testing, the method here shown may be employed. For
this purpose, however, two motors, preferably of the same size and
type, are required. One is driven as a motor and runs slightly below
synchronism, due to its slip when operating with load. This motor is
belted to a second machine. If the pulley of the second machine be
smaller than the pulley of the first machine, the second machine will
then operate as an induction generator, and will return to the line
as much power as the first motor draws from the line, less the losses
of the second machine. By properly selecting the ratio of pulleys,
the first machine can be caused to draw full load current and full
load energy from the line. In this way, the total energy consumed
is equivalent to the total of the losses of both machines, which is
approximately twice the losses of a single machine. The figure shows
the connection of the wattmeters, without necessary switches, for
reading the total energy by two wattmeter method. Detailed connection
of the wattmeter is shown in fig. 2,883. It is usual, in making
temperature tests, to insert one or more thermometers in what is
supposed to be the hottest part of the winding, one on the surface
of the laminae and one in the air duct between the iron laminae. The
test should be continued until the difference in temperature between
any part of the motor and the air reaches a steady value. The motor
should then be stopped and the temperature of the armature also
measured. For the method of testing wound armature type induction
motors of very large size, see fig. 2,890. For the approved way
of taking temperature readings and interpreting results, see the
"Standardization Rules of the A.I.E.E."]

=Ques. Describe a two scale voltmeter.=

Ans. In this type of instrument, one scale is for low voltage
readings and the other for high voltage readings; on these scales
the values of the graduations for low voltages are usually marked
with red figures, while those for high voltages are marked with
black figures. A voltmeter carrying two scales must also contain two
resistances in place of one; a terminal from each of these coils must
be connected with a separate binding post, but the remaining terminal
of each resistance is joined to a wire which connects through the
fine wire coil with the third binding post of the meter. The two
first mentioned binding posts are usually mounted at the left hand
side of the meter and the last mentioned binding post and key at the
right hand side.

[Illustration: FIG. 2,887.--Alternator excitation or magnetization
curve test. The object of this test is to determine the change of
the armature voltage due to the variation of the field current when
the external circuit is kept open. As here shown, the field circuit
is connected with an ammeter and an adjustable resistance in series
with a direct current source of supply. The adjustable resistance is
varied, and readings of the voltmeter across the armature, and of
the ammeter, are recorded. The speed of the generator must be kept
constant, preferably at the speed which is given on the name plate.
The excitation or magnetization curve of the machine is obtained by
plotting the current and the voltage.]

     The resistance corresponding to the high reading scale is
   composed of copper wire having the same diameter as that
   constituting the resistance for the low reading scale, but as the
   capacity of the former scale is generally a whole number of times
   greater than that of the latter scale, the resistances for the two
   must bear the same proportion.

[Illustration: FIG. 2,888.--Three phase alternator synchronous
impedance test. In determining the regulation of an alternator, it
is necessary to obtain what is called the _synchronous impedance_ of
the machine. To obtain this, the field is connected, as shown above.
Voltmeters are removed and the armature short circuited with the
ammeters in circuit. The field current is then varied, the armature
driven at synchronous speed, and the armature current measured by
the ammeters in circuit. The relation between field and armature
amperes are then plotted. The combination of the results of this
test, with those obtained from the test shown in fig. 2,887, are used
in the determination of the regulation of an alternator. Engineers
differ widely in the application of the above to the determination
of regulation, and employ many empirical formulae and constants for
different lines of design.]

=Ques. How is a two scale voltmeter connected?=

Ans. In the connection of a two scale voltmeter in circuit, the
single binding post is always employed regardless of which scale is
desired. If, then, the voltage be such that it may be measured on the
low reading scale, the other binding post employed is that connected
to the lower of the two resistances contained within; if, however,
the pressure be higher than those recorded on the low reading scale,
the binding post connected to the higher of the two resistances
contained within is used.

            NOTE.--Three phase alternator load test. By
          means of the connection shown in fig. 2,888,
          readings of armature current and field amperes
          can be obtained with any desired load. The field
          current can be varied also so as to maintain
          constant armature voltage irrespective of load;
          or the field current may be kept constant and
          the armature voltage allowed to vary as the load
          increases. The connections may also be used to
          make a temperature test on the alternator by
          loading it with an artificial load. In some cases
          after the alternator is installed the connection
          may be used to make a temperature test, using
          the actual commercial load the alternator is
          furnishing.

            Inasmuch as the capacities of the scales are
          usually marked on or near the corresponding
          binding posts, there will generally be no
          difficulty in selecting the proper one of the two
          left hand binding posts.

[Illustration: FIG. 2,889.--Three phase alternator or synchronous
motor temperature test. In this test two alternators or synchronous
motors of same size and type are used, and are belted together, one
to be driven as a synchronous motor and the other as an alternator.
The method employed is to synchronize the synchronous motor with
the alternator or alternators on the three phase circuit, and then
connect to the line by means of a three pole single throw switch.
The alternator is then similarly synchronized with the alternator
of the three phase circuit and thrown onto the line. By varying the
field of the alternator it can be made to carry approximately full
load, and the motor will then be also approximately fully loaded.
The usual method is to have the motor carry slightly in excess of
full load, and the alternator slightly less than full load. Under
these conditions the motor will run a little warmer than it should
with normal load, while the alternator will run slightly cooler.
Temperature measurements are made in the same way as discussed
under three phase motors. The necessary ammeters, voltmeters and
wattmeters for adjusting the loads on the motors and generator are
shown in above figure. If pulleys be of sufficient size to transmit
the full load, with, say one per cent. slip, the pulley on the motor
should be one per cent. larger in diameter than the pulley on the
alternator, so as to enable the alternator to remain in synchronism
and at the same time deliver power to the circuit. With very large
machines under test, it is inadvisable to use the above method as
it is sometimes difficult to so adjust the pulleys and belt tension
that the belt slip will be just right to make up for the difference
in diameter of the pulleys, and very violent flapping of the belt
results. To meet such cases, various other methods have been devised.
One which gives consistent results is shown in fig. 2,890.]

=Ques. How is a two scale voltmeter connected when the binding posts
are not marked?=

Ans. If only an approximate idea is possessed of the voltage to be
measured, it is always advisable to connect to the binding post
corresponding to the high reading scale of the meter in order
to determine if the measurement may not be made safely and more
accurately on the low reading scale. In any case, some knowledge must
be had of the voltage at hand, else the high reading portion of the
instrument may be endangered.

[Illustration: FIG. 2,890.--Three phase alternator or synchronous
motor temperature test. Supply the field with normal field current.
The armature is connected in open delta as illustrated, and full load
current sent through it from an external source of direct current,
care being taken to ground one terminal of the dynamo so as to avoid
danger of shock due to the voltage on the armature winding. The field
is then driven at synchronous speed. If the armature be designed to
be connected star for 2,300 volts, the voltage generated in each leg
of the delta will be 1,330 volts, and unless one leg of the dynamo
were grounded, the tester might receive a severe shock by coming
in contact with the direct current circuit. The insulation of the
dynamo would also be subjected to abnormal strain unless one terminal
were grounded. By the above method the field is subjected to its
full copper loss and the armature to full copper loss and core loss.
Temperature readings are taken as per standardization rules of the
A.I.E.E. This method may also be used with satisfactory results on
large three phase motors of the wound rotor type. If the alternator
pressure be above 600 volts, a pressure transformer should be used in
connection with the voltmeter.]

     _Too much care cannot be taken to observe these precautions_
   whenever the voltmeter is used, for the burning out or charring
   of the insulation either in the fine wire coil or in the high
   resistance of the meter by an excessive current, is one of the
   most serious accidents that can befall the instrument.

     If a voltmeter has been subjected to a voltage higher than that
   for which it was designed, yet not sufficiently high to injure the
   insulation, but high enough to cause the pointer to pass rapidly
   over the entire scale, damage has been done in another way. The
   pointer being forced against the side of the case in this manner,
   bends it more or less and so introduces an error in the readings
   that are afterward taken.

     The same damage will be done if the meter be connected in
   circuit so the current does not pass through it in the proper
   direction, although in this case the pointer is not liable to
   be bent so much as when it is forced to the opposite side of
   the meter by an abnormal current, since then it has gained
   considerable momentum which causes a severer impact. The extent
   of the damage may be ascertained by noting how far away from the
   zero mark the pointer lies when no current is passing through
   the instrument. If this distance be more than two-tenths of a
   division, the metal case enclosing the working part should be
   removed and the pointer straightened by the careful use of a pair
   of pinchers.

[Illustration: FIG. 2,891.--Direct motor or dynamo magnetization
test. The object of this test is to determine the variation of
armature voltage without load, with the current flowing through the
field circuit. The armature should be driven at normal speed. The
adjustment resistance in the field circuit is varied and the voltage
across the armature measured. The curve obtained by plotting these
two figures is usually called magnetization curve of the dynamo. It
is usual to start with the higher resistance in the field circuit so
that very small current flows, gradually increasing this current by
cutting out the field resistance. When the highest no load voltage
required is reached, the field current is then diminished, and what
is called the descending (as opposed to the ascending) magnetization
curves are obtained. The difference in the two curves is due to the
lag of the magnetization behind the magnetizing current, and is
caused by the hysteresis of the iron of the armature core.]

=Ques. What should be noted with respect to location of instruments?=

Ans. If they be placed near conductors carrying large currents,
the magnetic field developed thereby will produce a change in the
magnetism of the instruments and so introduce an error in the
readings.

[Illustration: FIG. 2,892.--Shunt dynamo external characteristic
test. The external characteristic of a shunt dynamo is a curve
showing the relation between the current and voltage of the external
circuit. This is obtained by the connection as here shown. The shunt
field is so adjusted that the machine gives normal voltage when
the external circuit is open. The field current is then maintained
constant and the external current varied by varying the resistance
in the circuit. By plotting voltage along the vertical, against the
corresponding amperes represented along the horizontal, the external
characteristic is obtained.]

=Ques. How should portable instruments be wired?=

Ans. The wires must be firmly secured to the supports on which they
rest, so as to reduce the possibility of their being pulled by
accident, and so causing the instruments to fall.

     A fall or a rough handling of the meter at once shows its effect
   on the readings, for as much harm is done as would result from a
   similar treatment of a watch.

     The hardened steel pivots used in all high grade voltmeters are
   ground and polished with extreme care so as to secure and maintain
   a high degree of sensitiveness. The jewels on which the moving
   parts revolve are of sapphire, and they too must necessarily be
   made with skill and carefulness; if, therefore, the jewels become
   cracked and the pivots dulled by careless handling, the meter at
   once becomes useless as a measuring instrument.

=Ques. How should readings be taken?=

Ans. The deflection of the pointer should be read to tenths of a
division; this can be done with considerable accuracy, especially
after a little practice.

[Illustration: FIG. 2,893.--Load and speed test of direct current
shunt motor. The object of this test is to maintain the voltage
applied to the motor constant, and to vary the load by means of a
brake and find the corresponding variation in speed of the machine
and the current drawn from the circuit. If the motor be a constant
speed motor, the field resistance is maintained constant. The above
indicates the method of connecting instruments for the test alone;
for starting the machine the ordinary starting box, should, of
course, be inserted.]

     For very accurate results, a temperature correction should be
   applied to compensate the effect which the temperature of the
   atmosphere has upon the resistance of the meter when measurements
   are being taken. In ordinary station practice the temperature
   correction is negligible, being for resistance corresponding to
   the high scale in first class meters, less than one-quarter of 1
   per cent. for a range of 35 degrees above or 35 degrees below 70
   degrees Fahrenheit.

=Ques. What attachment is sometimes provided on station voltmeters
used for constant pressure service?=

Ans. A normal index.

[Illustration: FIG. 2,894.--Temperature test of direct current
motor or dynamo; loading back method. In making temperature tests
on a small dynamo it is usual to drive the dynamo with a motor and
load the dynamo by means of a lamp bank or resistance, the voltage
across the dynamo being maintained constant, and the current through
the external circuit adjusted to full load value. The temperatures
are then recorded, and when they reach a constant value above the
temperature of the atmosphere, the test is discontinued. Similarly,
in making a test on a small motor, the motor is loaded with a dynamo
and the load increased until the input current reaches the normal
full load value of the motor, the test being conducted as for a small
dynamo. When, however, the apparatus, either motor or dynamo, reaches
a certain size, it becomes necessary, in order to economize energy,
to use what is called the =loading back method=, as here illustrated.
The motor is started in the usual way, with the dynamo belted to it,
the circuit of the dynamo being open. The field of the dynamo is then
adjusted so that the dynamo voltage is equal to that of the line.
The dynamo is then connected to the circuit and its field resistance
varied until it carries normal full load current. Under these
conditions, if the motor and dynamo be of the same size and type,
the motor will carry slightly in excess of full load, the difference
being approximately twice the losses of the machines. Under these
conditions the total power drawn from the line is equal to twice the
loss of either machine. Temperature readings are taken as in other
temperature tests.]

=Ques. What precaution must be taken in connecting station
voltmeters?=

Ans. Care must be taken to guard against any short circuiting of the
voltmeter, which, would mean a short circuiting of the generator, and
as a result the probable burning out of its armature.

     The high resistance of the voltmeter prevents any such
   occurrence when it is connected in the proper way, but should one
   side of the circuit be grounded to the metal case or frame of the
   meter, a careless handling of the lead connected with the other
   side of the circuit would produce the result just mentioned.

[Illustration: FIG. 2,895.--Compound dynamo external characteristics
test; adjustable load. The object of this test is to determine the
relation between armature voltage and armature current. Shunt field
is adjusted to give normal secondary voltage when the external
circuit is open. The load is then applied by means of an adjustable
resistance or lamp bank, and readings of external voltage and current
recorded. If the machine be normally compounded, the external voltage
will remain practically constant throughout the load range. If the
machine be under-compounded, the external voltage will drop with
load, while if over-compounded, there will be a rise in voltage with
increase in load.]

=Ques. Why do station voltmeters indicate a voltage slightly lower
than actually exists across the leads?=

Ans. Since they are usually connected permanently in circuit; a
certain amount of heat is developed in the wiring of the instrument.

[Illustration: FIGS. 2,896 and 2,897.--Transformer core loss and
leakage, or exciting current test. With the primary circuit open,
the ammeter indicates the exciting or no load current. It should
be noted that all instruments are inserted on the low voltage
side, for both safety of the operator and because the measurements
are more accurate. The no load primary current, if the ratio of
transformation be 10: 1, will be one-tenth of the measured secondary
current. The wattmeter connected, as shown, measures the sum of the
losses, in the transformer, in the pressure coil of the wattmeter,
and in the voltmeter. On all standard makes of portable instruments,
the resistance of the wattmeter pressure coil and of the voltmeter
is given, and the loss in either instrument is the square of the
voltage at its terminals, divided by its resistance. Subtracting
these losses from the total indicated upon the wattmeter, gives the
true core or iron loss. It should be noted that in this diagram is
shown an auxiliary transformer with a number of taps for obtaining
the exact rated voltage of the transformer under test. In fig. 2,897
is shown, in general, the same connections as in fig. 2,896, except
that the auto-transformer has been replaced by a resistance. If the
line voltage available be not much in excess of the rated voltage of
the transformer under test, very little error is introduced by the
use of the resistance method. However, if the difference be 10 per
cent. or more the auxiliary transformer shown in fig. 2,896 should be
used. Measurements made under the resistance method always give lower
results than those obtained with the auxiliary transformer.]

     The effect of this heat increases the voltmeter resistance and
   consequently reduces the current below that which otherwise would
   pass through the meter; since the deflections of the pointer
   are governed by the strength of the current, station voltmeters
   invariably indicate a voltage slightly lower than that which
   actually exists across their leads.

[Illustration: FIG. 2,898.--Diagram of connections for calibrating a
wattmeter. The calibration of a portable wattmeter is accomplished
with direct current of constant value which is passed through the
series winding by connecting the source thereof with the current
terminals. A direct current voltage which may be varied throughout
the range of the wattmeter is also applied to the instrument
between the middle and right hand pressure terminals A and E the
wiring in the meter between these terminals being such that its
differential winding is then cut out of circuit. The method of
procedure consists in comparing the deflections on the wattmeter at
five of six approximately equidistant points over its scale with the
corresponding products of volts and amperes used to obtain them. The
changes in the wattmeter deflections are effected by merely varying
the voltage, the value of the current being maintained constant at a
value which represents the full current capacity of the meter.]

            NOTE.--=Checking up of a recording wattmeter.=
          This may conveniently be done by noting the
          deflections at short intervals on an ammeter
          connected in circuit, and also the readings
          on the dial of the recording wattmeter during
          this period. If this test be continued for an
          appreciable time, the product of the pressure
          in volts, the current in amperes, and the time
          in hours, should equal the number of watthours
          recorded on the counters of the dial.

            NOTE.--=Transformer testing.= In the early
          days of transformer building, before the
          commercial wattmeter had been perfected, leakage
          or exciting current was the criterion of good
          design. After the introduction of the wattmeter,
          core loss became the all important factor, and
          for a long time the question of leakage current
          was lost sight of. With the introduction of
          silicon steel, leakage or exciting current again
          assumed prominence. Keeping in mind the fact
          that all characteristics of a transformer are of
          more or less importance, it is essential that
          the user of such apparatus have at hand the
          necessary facilities for making tests of all such
          variable quantities. The tests which all users
          of transformers should make, are given in this
          chapter.

=Ques. Can direct current be measured by an alternating current
voltmeter?=

Ans. Yes.

[Illustration: FIG. 2,899.--Transformer copper loss by wattmeter
measurement and impedance. At first glance, this method would
seem better than the calculation of loss after measurement of the
resistance. However, it should be noted that the wattmeter is, in
itself, subject to considerable error under the low power factor
that will exist in this test. The secondary of the transformer is
short circuited, and a voltage applied to the primary which is just
sufficient to cause full load primary current. If full current pass
through the primary of the transformer with the secondary short
circuited, the secondary will also carry full load current. With
connections as shown, and with the full load current, the voltmeter
indicates the impedance volts of the transformer. This divided by
the rated voltage gives what is called the _per cent. impedance of
the transformer_. In a commercial transformer of 5 kw., this should
be approximately 3 per cent. The iron loss of the transformer under
approximately 3 per cent. of the normal voltage will be negligible,
and the losses measured will be the sum of the primary and secondary
copper losses. As in the discussion of the core loss measurements,
the wattmeter readings must be corrected for the loss in its pressure
coil, the method of correction being the same as that discussed under
the core loss measurement. If the impedance volts, as measured, be
divided by the primary current, the impedance of the transformer
is obtained. The reciprocal of this quantity is known by the term
"admittance." _When two or more transformers are connected in
parallel they divide the load in proportion to their admittance._
It is, therefore, important that the users of transformers know the
impedance of the apparatus used, in order to determine whether two
or more transformers will operate satisfactorily in parallel. For
discussion of wattmeter error on low power factor, see note on page
2,075. For accurate measurement of impedance, the voltmeter should
be connected directly across the terminals of the transformer rather
than as shown in the diagram.]

            NOTE.--=Transformer copper loss test.= The
          usual and best method of obtaining copper
          losses is to separately measure the primary and
          secondary resistance and calculate from these
          the primary and secondary copper losses. For
          general diagram of connections and discussion
          of the drop method, see fig. 2,875. The current
          should be kept well within the load current of
          the transformer to avoid temperature rise during
          the test. In other words, the resistance of the
          coil is the voltage across its terminals divided
          by the current. The resistance of the primary
          coil can be measured similarly. The copper loss
          in watts in each coil will then be the product
          of the resistance and the square of the rated
          current for that coil. The total copper loss will
          be the sum.

=Ques. What would be the effect of placing a direct voltmeter across
an alternating current circuit, and why?=

Ans. There would be no deflection of the pointer owing to the rapid
reversals of the alternating current.

=Ques. What are the usual capacities of alternating current
voltmeters?=

Ans. They are 3, 7.5, 10, 12, 15, 20, 60, 75, 120, 150, 300 and 600
volts, but these capacities may each be increased by the use of a
multiplier.

[Illustration: FIG. 2,900.--Temperature test of transformer with
non-inductive load. The figure shows the simplest way of making the
test. Connect the primary of the transformer to the line as shown,
and carry normal secondary load by means of a bank of lamps or other
suitable resistance, until full load secondary current is shown by
the ammeter in the secondary circuit. The transformer should then be
allowed to run at its rated load for the desired interval of time,
temperature readings being made of the oil in its hottest part, and
also of the surrounding air. Where temperatures of the coil rather
than temperatures of the oil are desired, it is necessary to use the
resistance method. This is obtained by first carefully measuring the
resistance of both primary and secondary coils at the temperature
of the room, and then, after the transformer has been under heat
test for the desired time, disconnect it from the circuit and again
measure the resistance of primary and secondary. For proper method
of calculating the temperature rise from resistance measurements,
the reader is referred to the standardization rules of the A.I.E.E.
In making resistance measurements of large transformers by the drop
method care should be taken to allow both ammeter and voltmeter
indications to settle down to steady values before readings are
taken. This may require several minutes. Each time the current is
changed it is necessary in order to obtain check values on resistance
measurements, to wait until the current is again settled to its
permanent value before taking readings. All resistance measurements
must be taken with great care, as small errors in the measurement of
the resistance may make very large errors in the determination of
the temperature rise. The method above described is satisfactory for
small transformers. Where large units are to be tested, the cost of
current for testing becomes an important item. The "bucking test" as
in fig. 2,901, is more economical.]

=Ques. How are station voltmeters usually attached to the
switchboard?=

Ans. They are usually bolted to the switchboard by means of four
iron supports mounted on the back of the instrument; two of these are
fastened near each side of the case.

     Under certain conditions, however, as in paralleling of
   alternators, it is convenient to have the alternating current
   voltmeter mounted on a swinging bracket at the side of the
   switchboard. The voltmeter may then be swung around in any desired
   direction so as to enable the attendant to keep informed of the
   voltage while switching in each additional alternator.

[Illustration: FIG. 2,901.--Transformer temperature "bucking test."
For this purpose two transformers of the same size and ratio are
required. The connections are as shown. Full secondary voltage is
applied, and rheostats or auxiliary auto-transformers are inserted
in the circuit to properly regulate the voltage. The primaries
are connected with one bucking the other, and a voltage equal to
twice the impedance voltage of either transformer inserted in the
primary circuit. It should be noted that when the secondaries are
subjected to the full secondary voltage, a full primary voltage
exists across either primary, but with the primaries connected so
that the voltage of one is bucked against the voltage of the other,
the resultant voltage in the circuit will be zero. By applying to the
primary circuit twice the impedance voltage of either transformer,
full primary and secondary current will circulate through both
transformers. On the other hand, by subjecting the secondaries to
the full secondary voltage, the iron of the transformer will be
magnetized as under its regular operating conditions, and the full
iron loss of the transformer introduced. This method permits the
operation of two transformers under temperature test with their
full losses, without taking energy from the line equal to the rated
capacity. Measurements of temperature are taken in exactly the
same way as above. This method is successfully employed for making
temperature tests on transformers of all sizes.]

=Ques. How should an ammeter be operated to get accurate readings,
and why?=

Ans. It should be cut out of circuit except while taking a reading,
because of the error introduced by the heating effect of the current.

[Illustration: FIG. 2,902.--Transformer insulation test. In applying
a 10,000 volt insulation test between the primary and secondary of
a transformer, the testing leads should be disconnected from the
transformer under test, and a spark gap introduced as shown, with the
test needle set at a proper sparking distance for 10,000 volts. A
high resistance should be connected in the secondary before closing
its circuit, and the voltage gradually increased by cutting out
this secondary resistance until a spark jumps across the spark gap.
When the spark jumps across the spark gap, the voltmeter reading
should be recorded and the testing transformer disconnected. The
spark gap should then be increased about 10 per cent. and the high
tension leads connected to the transformer under test as indicated
in the diagram. In order to equalize the insulation strains, all
primary leads should be connected together, all secondary leads not
only connected together, but to the core as well. All resistance
in the rheostat in the low tension circuit should then be inserted
and the switch closed. Gradually cut out secondary resistance until
the voltmeter shows the same voltage as was recorded previously
when the spark jumped across the gap, and apply this voltage to the
transformer for one minute. Insulation tests for a period of over
one minute are very unadvisable, as transformers with excellent
insulation may be seriously damaged by prolonged insulation tests.
The longer the strain to which any insulation is subjected, the
shorter the subsequent life of the insulation. Also the greater the
applied voltage above the actual operating voltage of the apparatus,
the shorter the subsequent life of the insulation. In testing small
transformers, the spark gap may be omitted and the voltage of the low
pressure coil of the testing transformer measured. This multiplied by
the ratio of transformation gives the testing voltage.]

     In an ammeter having a capacity of 50 amperes, the error thus
   introduced will be less than 1 per cent. if connected continuously
   in circuit with a current not exceeding three-quarters this
   capacity.

     An ammeter of 100 amperes capacity may be used indefinitely
   in circuit with less than 1 per cent. error up to one-half its
   capacity, and for five minutes at three-quarters capacity without
   exceeding the 1 per cent. limit.

[Illustration: FIG. 2,903.--Transformer insulation test as made
when a special high tension transformer be not available. In this
method a number of standard transformers, connected as shown may be
employed, but great care should be taken to have such transformer
cases thoroughly insulated from the ground and from one another, in
order to minimize the insulation strains in the testing transformers.
Care should be taken to insert in the circuit of each testing
transformer a fuse, not in excess of the transformer capacity, which
will blow, in case of a break down in the apparatus under test.
In testing insulation between secondary and core, disconnect the
primary entirely, apply one terminal of the testing transformer to
the secondary terminals of the transformer under test, and the other
terminal of the testing transformer to the core of the transformer
under test. This test should also not be in excess of one minute.]

     The 150 scale ammeter may be left in circuit for an indefinite
   length of time at one-third its full capacity, and for three
   minutes at one-half its full capacity, with a negligible error.

     Ammeters of 200 and of 300 ampere capacities must not
   continuously carry more than one-quarter of these loads
   respectively if the readings are to have an accuracy within 1 per
   cent. nor more than one-half these respective number of amperes
   for three minutes if the same degree of accuracy be desired.

     In order to cut or shunt the ammeter out of circuit when not
   in use, it is customary when wiring the instrument in place, to
   introduce a switch as a shunt across it; this switch is kept
   closed except when a measurement is being taken.

     When currents larger than 300 amperes have to be measured,
   ammeter shunts are generally employed, although ammeters up to
   500 amperes capacity are manufactured.

[Illustration: FIG. 2,904.--Transformer internal insulation test,
sometimes called double normal voltage test, from the fact that most
transformers are tested with double normal voltage across their
terminals. If either the primary or secondary of the transformer
be connected to some source of current with voltage double that of
the voltage of the transformer under test, the insulation between
adjacent turns, and also the insulation between adjacent layers
will be subjected to twice the normal operating voltage. It is good
practice to employ high frequency for this test in order to prevent
an abnormal current from passing through the transformer. Sixty
cycle transformers are usually tested on 133 cycles, and 25 cycle
transformers on 60 cycle circuits for this double normal voltage
test. It is necessary to insert the resistance in the circuit of the
transformer and bring the voltage up gradually, the same as applying
other high insulation tests in order to prevent abnormal rises in
pressure at the instant of closing the circuit.]

=Ques. What is used in place of instrument shunts for high pressure
alternating current measurements?=

Ans. Instrument transformers.

=Ques. What important attention should be periodically given to
measuring instruments?=

Ans. They should be frequently tested by comparison with standards
that are known to be correct.

     Electrical measuring instruments, owing to the nature of their
   construction and the conditions under which they must necessarily
   be used, are subject to variations in accuracy. This feature is an
   annoying one on account of the difficulty of detecting it; a meter
   may, as far as appearances go, be in excellent working order and
   yet give readings which are not to be relied upon.

     Ridiculous as it may appear, the average station attendant
   may frequently be seen straining his eyes to read to tenths of
   a division on the scale of a meter which, if subjected to test,
   would show an inaccuracy of over 2 per cent.

     In testing a meter, by comparing it with a standard, in order to
   obtain the best results there should be one man at each meter so
   that simultaneous readings may be taken on both instruments, and
   the man at the standard meter should maintain the voltage constant
   while a reading is being taken, by means of a rheostat in the
   field circuit of the generator supplying the current.

[Illustration: FIG. 2,905.--Transformer insulation resistance
test. The insulation, besides being able to resist puncture, due
to increased voltage, must also have sufficient resistance to
prevent any appreciable amount of current flowing between primary
and secondary coils. It is, therefore, sometimes important that the
insulation resistance between primary and secondary be measured. This
can be done, as here shown. Great care should be taken to have all
wires thoroughly insulated from the ground, and to have an ammeter
placed as near as possible to the terminals of the transformer under
test, in order that current leaking from one side of the line to the
other, external to the transformer, may not be measured. Great care
is required in making this measurement, in order to obtain consistent
results.]

     Each meter should be checked or calibrated at five or six
   approximately equidistant points over its scale; the adjustable
   resistance being varied each time to give a deflection on the
   standard meter of an even number of divisions and the deflection
   on the other meter recorded at whatever it may be. Having obtained
   the necessary readings, the calculation of the constant or
   multiplying factor of the meter undergoing test is next in order.

     This may best be shown by taking an actual case in which a 150
   scale voltmeter is being tested to determine its accuracy. The
   data and calculations are as follows:

   Readings on     Readings on        Constant
  standard meter   meter tested
       150            149.2        150 ÷ 149.2 = 1.005
       125            125.0        125 ÷ 125.0 = 1.000
       100             98.9        100 ÷  98.9 = 1.011
        75             73.6         75 ÷  73.6 = 1.019
        50             50.0         50 ÷  50.0 = 1.000
        25             24.8         25 ÷  24.8 = 1.008
                                                ------
                                                 6.043

  Average constant for six readings, 6.043 ÷ 6 = 1.007.

[Illustration: FIG. 2,906.--Transformer winding or ratio test. The
object of this test is to check the ratio between the primary and
the secondary windings. For this purpose a transformer of known
ratio is used as a standard. Connect the transformer under test with
a standard transformer as shown. Leave switch S_{2} open. With the
single pole double throw switch in position S_{1}B, the voltmeter
is thrown across the terminals of the standard transformer. With
the switch in position S_{1}A, the voltmeter is thrown across the
terminals of the transformer under test. The voltmeter should be read
with the switch in each position. If the winding ratio be the same as
that of the standard transformer, the two voltmeter readings will be
identical.]

     It may be stated in general that before taking the readings for
   this test, the zero position of the pointer on the meter tested
   should be noted, and if it be more than two-tenths of a division
   off the zero mark, the case of the meter should be removed and the
   pointer straightened.

     Furthermore, it will be noticed from the readings here recorded
   that the test is started at the high reading end of the scale;
   this is done in order that the pointer may gradually be brought
   up to this spot, by slowly cutting out of circuit the adjustable
   resistance, and thus show whether or not the pointer has a
   tendency to stick at any part of the scale. If the meter seem to
   be defective in this respect, it should be remedied either by
   bending the pointer or scale, or by renewing one or both of the
   jewels, before the comparison with the standard is commenced.

     It is obvious from the readings recorded for the 150 scale
   voltmeter, that as compared with the corresponding deflections of
   the standard, the former are a trifle low.

     In order to determine for each observation how much too low
   they are, it is necessary to divide each reading on the standard
   by the corresponding reading on the meter tested. The result is
   the amount by which a deflection of this size on the meter tested
   must be multiplied in order to obtain the exact reading. This
   multiplier is called a constant, and as shown, a constant is
   determined for each of the six observations.

     The average constant for the six readings is then found, and
   this is taken as the constant for the meter as a whole; that is,
   whenever this 150-scale voltmeter is used, each reading taken
   thereon must be multiplied by 1.007 in order to correct for its
   inaccuracy.

     The most convenient and systematic way of registering the
   constant of a meter is to write it, together with the number of
   the meter and the date of its calibration, in ink on a cardboard
   tag and loop the same by means of a string to the handle or some
   other convenient part of the meter.

            NOTE.--=Transformer polarity test.= A test of
          importance in the manufacture of transformers,
          and sometimes necessary for the user, is the
          so called _banking_ or _polarity_ test. The
          transformers from any particular manufacturer
          have the leads brought out in such a manner that
          a transformer of any size can be connected to
          primary and secondary lines in a given order
          without danger of blowing the fuses due to
          incorrect connections. All manufacturers of
          transformers, however, do not bank transformers
          in the same way, so that it is necessary in
          placing transformers of different makes to test
          for polarity. This is done as shown in fig.
          2,906. One transformer is selected as a standard
          and the leads of the second transformer connected
          as indicated in the diagram. If the transformers
          be 1,100-2,200 volts to 110-220, two 110 volt
          lamps are connected in the secondaries of the
          transformers as indicated, while the primary of
          the transformer is connected across the line.
          In transformers built for two primary and two
          secondary voltages, it is necessary to test each
          primary and each secondary. The diagram shows the
          method of connecting one 2,200 volt coil and one
          110 volt coil to the transformer to be tested.
          When the primary circuit of the transformer under
          test is closed, and if the secondary leads of
          the 110 volt coil under test be brought out of
          the case properly, the two 110 volt lamps should
          be brightly illuminated. If, on the other hand,
          the two 110 volt terminals have been reversed,
          no current will flow through the lamps. If
          these two terminals be found to be brought out
          correctly, transfer the secondary leads of the
          transformer under test to the second 110 volt
          coil. Upon closing the primary circuit, the lamp
          should again be brightly illuminated. Repeat this
          process with each of the secondary coils and the
          other primary coil, and if the lamps show up
          brightly in every case on closing the primary
          circuit, all leads have been properly brought
          out. If on any tests the lamps do not light up
          brightly, the leads on the transformer must be so
          changed as to produce the proper banking.

=Ques. What are the usual remedies applied to a voltmeter to correct
a 3 or 4 per cent. error?=

Ans. They consist of straightening the pointer, varying the tension
of the spiral springs, renewing the jewels in the bearings, altering
the value of the high resistance, and, in the case of a direct
current instrument, strengthening the permanent magnet.

=Ques. How is the permanent magnet strengthened?=

Ans. After detaching it from the instrument, wrap around several
turns of insulated wire, and pass through this wire for a short time
3 or 4 amperes of direct current in such a direction as to reinforce
the magnet magnetism.

=Ques. How may the value of the high resistance of a voltmeter be
altered?=

Ans. Determine the resistance of the voltmeter and add or subtract,
according as the reading is high or low, a certain length of wire
whose resistance is in per cent. of the voltmeter resistance the same
as the per cent. of error.

            NOTE.--The complete calibration of a two
          scale voltmeter does not, as might be supposed,
          necessitate that the readings on both scales be
          checked with standards, for since the resistance
          corresponding to the one scale is always some
          multiple of the resistance of the other, the
          constants of the two scales are proportional. For
          instance, if S = the reading at the end of the
          high scale of the voltmeter; S^{1} = the reading
          at the end of the low scale of the voltmeter; R =
          the resistance in the meter corresponding to the
          high scale; R^{1} = the resistance in the meter
          corresponding to the low scale; K = the constant
          for the high scale, and K^{1} = the constant for
          the low scale. Then

           SK ÷ R = S^{1}K^{1} ÷ R^{1}

from which

           K^{1} = SKR ÷ S^{1}R

     That is to say, if the respective resistances corresponding to
   the two scales be known, and the constant of the high scale be
   determined by comparison with a standard, then by aid of these
   known values and the maximum readings on the two scales, the
   constant of the low scale may be calculated. It is also possible
   to calculate the constant of the high scale if the constant of the
   low scale be known, together with the values of the resistances
   corresponding to the two scales; for from the equation previously
   given.

           K = RS^{1}K^{1} ÷ R^{1}S

=Ques. What is a frequent cause of error in an alternating current
meter, and why?=

Ans. The deterioration of its insulation, which permits the working
parts of the instrument coming in contact with the surrounding metal
case.

     A convenient method of testing for deterioration of insulation
   is shown in fig. 2,905.

[Illustration: FIG. 2,907.--Diagrams showing various synchronous
converter transformer connections. The diametrical connection is
used most frequently as it requires only one secondary coil on each
transformer, this being connected to diametrically opposite points on
the armature winding. The middle points can be connected together and
a neutral obtained the unbalanced three wire direct current having no
distorting effect. With diametrical secondaries, the primaries should
preferably be connected delta, except with regulating pole converters
where they must be connected Y. Diametrical secondaries with delta
primaries should not be used with regulating pole converters. Double
star connection of secondaries may, however, be used with delta
primaries, and is free from the trouble of the triple harmonic of the
transformer appearing in the primary. In this case, however, the two
secondary neutrals must not be connected with each other.]

=How to Test Generators.=--In the operation of electrical stations,
many problems dealing with the generators installed therein can be
readily solved by the aid of characteristic curves, which bear a
relation to the generators similarly as do indicator diagrams to
steam engines.

[Illustration: FIG. 2,908.--General form of characteristic curves
for a series dynamo. The general curve that may be expected is OA.
It is obtained practically in the same manner as for the shunt
characteristic curve, except that no field rheostat is employed.
Commencing with no load or amperes, there will probably be a
small deflection noticeable on the voltmeter, due to the residual
magnetism. The other readings are taken with successive reductions
of main current resistance. The curve OA thus obtained for a certain
series generator is practically a straight line at the beginning,
representing thereby a proportional increase of voltage with
increase of current, but after a certain current is reached (about
20 amperes in this case) the curve flattens and takes a downward
direction. The turning point occurs in the characteristic curves
of all series generators, and it denotes the stage at which the
iron magnet cores become so saturated with lines of magnetic force
that they will not readily allow more to pass through them; this
turning point is technically known as the point of saturation, and
the current corresponding (20 amperes in this case) is called the
critical current of the dynamo. The point of saturation in any given
series machine is governed by the amount of iron in the magnetic
circuit; its position in the curve therefore varies according to
the design of the generator as does also the critical current. The
value of the latter is important inasmuch as the valuable features
of a series generator assert themselves only when the machine is
supplying a greater number of amperes than that of the critical
current, for if the series generator be worked along that part M A of
the curve to the right of the point of saturation it becomes nearly
self-regulating as regards current, because as the current increases
the voltage drops. In the diagram in addition to the characteristic
curve O A, which may more definitely be called an external
characteristic curve on account of representing the conditions
external to the generator, there is shown a total characteristic
curve, O C B. The latter curve represents the relation between the
current and the total voltage developed in the armature, and may be
plotted from the external characteristic curve if the resistance of
the armature between brushes and the resistance of the series field
winding be known. For example, assume these combined resistances
amount to .6 ohm. At 30 amperes there would be required 30 × .6 = 18
volts to force this current through the armature and field windings.
At 30 amperes the external pressure is 65 volts, as shown by the
curve O A; the total voltage developed for 30 amperes is, therefore,
the external voltage plus the internal voltage or 65 + 18 = 83
volts. Plotting 83 volts for 30 amperes will give one point for the
external characteristic curve of this machine, and by determining in
like manner the total voltages developed for six or eight different
currents over the scale, sufficient data will be at hand for plotting
and drawing in the curve O C B.]

In steam engineering, a man who did not fully understand the method
of taking an indicator diagram would be considered not in touch with
his profession, and in electrical engineering the same would be true
of one ignorant of the method of obtaining characteristic curves.

     The necessary arrangement or connection of the generator from
   which it is desired to obtain a characteristic curve, consists in
   providing a constant motive power so that the machine may be run
   at a uniform speed, and when the field magnets of the generator
   are separately excited the field current from the outside source
   must also be maintained constant, preferably by a rheostat
   connected in the field of the auxiliary exciting machine. It is
   also necessary in every case that means be provided for varying
   the main current of the generator step by step from zero to
   maximum. This may best be done by employing a water rheostat, as
   shown in fig. 2,909.

=Ques. What instruments are needed in making a test of dynamo
characteristics?=

Ans. A voltmeter, ammeter, speed indicator, the usual switches and
rheostats.

=Ques. How is the apparatus connected?=

Ans. It is connected as shown in fig. 2,910.

=Ques. Describe the test.=

Ans. Having completed the preliminaries as in fig. 2,910, the test
should be started with the main circuit of the generator open. Then,
in the case of the shunt machine, the speed should be made normal and
the field rheostat adjusted until the voltmeter reading indicates
the rated voltage of the machine at no load and readings taken. The
electrodes of the water rheostat should be adjusted for maximum
resistance and main circuit closed, and a second set of readings
taken. Several sets of readings are taken, with successive reductions
of water rheostat resistance. The results are then plotted on
coordinate paper giving the characteristic curve shown in fig. 2,908.

[Illustration: FIG. 2,909.--Water rheostat. It consists essentially
of a tank of suitable size containing salt water into which are
placed two electrodes having means of adjustment of the distance
separating them. The solution depends on the voltage. Pure water is
seldom used for pressures under 1,000 volts. The size of the tank is
determined by the size of the electrodes, and roughly the size of the
latter equal the number of amperes. With a current density of one
ampere per square inch, a water solution gives a drop of 2,500 to
3,000 volts per inch distance between the plates. Where high voltage
is used, the water must be circulated through and from the tank by
rubber hose allowing for 2,500 volts, a length of 15 to 20 feet of
1 inch hose to prevent grounding. In place of the arrangement shown
above, a barrel may be used for the tank, and for the electrodes,
coils of galvanized iron wire. This is the simplest form and is
satisfactory.]

=Ques. What does the characteristic curve (fig. 2,911) show?=

Ans. An examination of the curve shows that the highest point of
the curve occurs at no load or 0 amperes; that as the current is
increased, the voltage drops, first slightly to the point B and then
rapidly until the point E is reached, when any further lowering of
resistance in the main circuit to increase the current causes not
only a rapid decline in the voltage but also of the current until
both voltage and current become approximately zero.

[Illustration: FIG. 2,910.--Connections for test of dynamo. During
the test, one man should be assigned to the tachometer, another man
to the water rheostat, and there should preferably be one man at
each of the electrical measuring instruments. In order to enable the
man at the tachometer to keep the speed constant, he should be in
communication either directly or indirectly with the source of the
driving power, and the man at the water rheostat should be in plain
view of the man reading the ammeter so that the latter party may
signal him for the proper adjustment of the rheostat in order that
the desired increase of current be obtained for each set of readings.]

     In some generators, a very slight current results even when the
   terminals of the machine are actually short circuited; that is,
   due to residual magnetism in the pole pieces, the lower portion of
   the curve often terminates, not exactly at zero, but at a point
   some distance along the current line.

     The working portion of the curve is from A to C, at which time
   the machine is supplying a fairly constant voltage. From C to E
   shows a critical condition of affairs, while the straight portion
   D O represents the unstable part of the curve caused by the field
   current being below its proper value.

     The position of the point C determines the maximum power the
   machine is capable of developing, being in this case (47.5 × 25) ÷
   746 = 1.59 horse power.

=Ques. How may the commercial efficiency of a generator be
determined?=

Ans. To obtain the commercial efficiency, the _input_ and _output_
must be found for different loads.

     The input may be found by running the generator as a motor
   at its rated speed, loading it by means of a Prony brake. The
   generator must be stripped of all belting or other mechanical
   connections, supplied with its normal voltage and full load
   current, and the pressure of the Prony brake upon its armature
   shaft or pulley adjusted until the rated speed of the armature is
   obtained. The data thus obtained is substituted in the formula.

                                         2π L W R
           input in brake horse power = ----------      (1)
                                          33,000

in which

           L = length of Prony brake lever;
           W = pounds pull at end of lever;
           R = revolutions per minute.

The output or electrical horse power for the same load is easily
calculated from the formula

                                     amperes × volts
           output in electrical horse power = ---------------  (2)
                                          746

After obtaining value for (1) and (2) the commercial efficiency for
the load taken is obtained from the formula

                                   output
           commercial efficiency = ------      (3)
                                    input

Having obtained the commercial efficiency, the difference between the
ideal 100 per cent. and the efficiency found will be due to certain
losses in the generator. These losses may be classified as

  1. Mechanical.
  2. Electrical.

     The mechanical losses are the friction of the bearings and
   brushes, and air friction. The electrical losses consist of the
   eddy current loss, hysteresis loss, armature resistance loss, and
   field resistance loss.

     In testing for these losses, the generator to be tested should
   be belted to a calibrated motor which latter machine should
   preferably be of the constant pressure, shunt wound type.

     The friction of the bearings and belt of the generator are
   determined together by raising the brushes off its commutator and
   running it at the rated speed by means of the calibrated motor.

[Illustration: FIG. 2,911.--Characteristic curve of shunt dynamo.
Suppose in making the test, the deflections on the meters for the
first readings be 63 volts and 0 amperes, the plotting of these
values will give the first point on the curve. Similarly, the second
readings with main circuit closed and maximum resistance in the water
rheostat may be assumed to be 62.5 volts and 7.5 amperes, which
plotted gives the second point B. A still further lowering of the
plate will permit a stronger current in the main circuit, and the
value of this together with its corresponding voltage will give a
third point for the curve. Neither for this reading, however, nor
for the following readings of the test should the field rheostat be
altered. When six or eight points ranging from zero to a maximum
current have been obtained and plotted, a curved line should be drawn
through them such as shown through ABCDEFG0, the _characteristic
curve_ of the dynamo. While the curve may be sketched in free hand,
it should preferably be drawn by the aid of French curves. In case
the French curve cannot be exactly made to coincide with all the
points as for instance C and D, it should be run in between giving an
average result, and smoothing out irregularities, or small errors due
to the "personal equation." The meter of course must be correct or
calibrated and the readings corrected by the calibration coefficient.]

     The amount of power as ascertained from the calibration curve of
   the motor for the voltage and current used therein when driving
   the generator as just explained, is a measure of these two losses.
   The power thus used is practically constant at all loads and is
   about 2 per cent. of that necessary to drive the generator at full
   load.

[Illustration: FIG. 2,912.--Characteristic curves for a compound
dynamo. If the machine be over compounded, the characteristic curve
has the form of the curve A B, which curve was obtained from a
machine over-compounded from 118 to 123 volts, and designed to give
203 amperes at full load. The preliminary arrangements for testing
a compound dynamo are similar to those for a shunt generator, and
if the shunt across the series field winding be already made up and
in position, the readings are taken precisely in the same manner.
It is generally considered sufficient if observations be recorded
at zero, ¼, ½, ¾ and full load. If it be desired to ascertain the
effect which residual magnetism has upon the field magnets the
current is decreased after the full load point is reached without
opening the circuit, and readings are taken in succession at ¾,
½, ¼ and zero load giving in this case the curve B C D E S. It is
thus seen that residual magnetism exerts no small effect upon the
voltage obtained at the different loads, for had there been no
residual magnetism in the field magnets the curve B C D E S would
have coincided with the curve A B. The curve A B, and the straight
line A X drawn through the points A and B, are almost identical,
and as A X represents the theoretical characteristic curve for the
machine, it is seen that compounding is practically perfect. In
order to insure such accurate results being obtained, providing
the machinery be correctly designed, requires considerable care in
taking the readings; for example, each step or load on the ascending
curve should not be exceeded before the corresponding deflection is
taken, else the residual magnetism will cause the pressure reading
to be higher than it actually should be, and the following pressure
readings will also be affected in the same manner. In case the shunt
to be employed across the series field has not been made up, it is
advisable to perform a trial test before taking the readings for the
curve as previously described. The trial test consists in taking
two readings,--one at no load and the other at full load, the shunt
being so adjusted as to length and section that the desired amount
of compounding will be obtained in the latter reading with normal
voltage at no load. If the first trial fail to produce the desired
result by giving too low a voltage at full load, the length of the
shunt across the series field should be increased, or its section
should be reduced by employing a less number of strips in its makeup;
again, if the voltage at full load be higher than that desired, there
must be made a decrease in length or an increase of section in the
shunt employed.]

     The friction of the brushes can very conveniently be determined
   next by lowering them on the commutator and giving them the proper
   tension.

     The increase in power resulting from the greater current that
   will now be taken by the motor to run the dynamo at its rated
   speed, will be a measure of this loss. In general, its value will
   be about .5 per cent. of the total power required to drive the
   dynamo at full load, and this also will remain constant at all
   loads.

     The friction of the air upon the moving armature of the dynamo
   cannot be determined experimentally, but theoretically this loss
   is small and may be estimated as .5 per cent.; it is also constant
   at all loads.

     The core loss may be determined experimentally by exciting
   the field magnets of the dynamo with the normal full load field
   current through the magnet coils, and noting the increase of power
   required by the motor to maintain the rated speed of the dynamo
   thus excited under no load, over that necessary under the same
   conditions with no field excitation. This increase of power will
   be the value of the core loss. The core loss is approximately 3
   per cent. of the power required to operate the dynamo at full
   load, and it is constant at varying loads. If it be desired to
   divide the core loss into its component parts, it is necessary
   also to run the dynamo under the same conditions as before with
   field excitation but at half its rated speed. If, then,

  H = the power lost in hysteresis at rated speed,
  E = the power lost in eddy currents at rated speed,
  T = the power lost in hysteresis and eddy currents at rated speed,
  S = the power lost in hysteresis and eddy currents at half speed.

there may be formed the two following equations:

                               H     E
           T = H + E, and S = --- + ---,
                               2     2

     from which the elimination of H will give E = 2T - 4S.

     The value of the eddy current loss thus found will be about 1½
   per cent., and constant at all loads.

     Having previously ascertained the power lost in both eddy
   currents and hysteresis, and knowing now the power lost in eddy
   currents alone, it is easy to find that lost in hysteresis by
   simply subtracting the latter known value from the former. The
   value of the hysteresis loss is therefore approximately 1½ per
   cent., and it is constant at different loads.

     There yet remains to be determined the armature resistance
   loss and the field resistance loss. As for the calibrated motor,
   this may be disconnected from the dynamo, as it need not be used
   further in the test.

     The armature resistance is the resistance of the armature
   winding of the dynamo, between the commutator bars upon which
   press the positive and negative brushes. Assume that the value
   of the armature resistance be known, call this value R ohms,
   together with that of the full load armature current, which is
   also known and which call I amperes, this is sufficient data for
   calculating the armature resistance loss at full load. It is
   evident that to force the full load current I through the armature
   resistance R will require a pressure of R volts, and that the
   watts lost in doing so will be the voltage multiplied by the
   current. The armature resistance is consequently

           IR × I = I^{2}R watts

or, expressed in horse power it is

           I^{2}R ÷ 746

     At full load it is usually about 2 per cent. of the total
   power required to drive the generator fully loaded. The armature
   resistance loss varies in proportion to the load, in fact, as the
   last expression shows, it increases as the square of the armature
   current.

     The field resistance loss is calculated in the same manner as
   just explained for the armature resistance loss, it being equal
   in horse power to the square of the full load field current
   multiplied by the resistance of the field winding and divided by
   746. In a shunt dynamo it is practically constant at 2 per cent.
   of the total power at full load, but in a series or in a compound
   generator it will vary in proportion to the load.



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=ELECTRICAL GUIDE, NO. 1=
     Containing the principles of Elementary Electricity, Magnetism,
   Induction, Experiments, Dynamos, Electric Machinery.

=ELECTRICAL GUIDE, NO. 2=
     The construction of Dynamos, Motors, Armatures, Armature
   Windings, Installing of Dynamos.

=ELECTRICAL GUIDE, NO. 3=
     Electrical Instruments, Testing, Practical Management of Dynamos
   and Motors.

=ELECTRICAL GUIDE, NO. 4=
     Distribution Systems, Wiring, Wiring Diagrams, Sign Flashers,
   Storage Batteries.

=ELECTRICAL GUIDE, NO. 5=
     Principles of Alternating Currents and Alternators.

=ELECTRICAL GUIDE, NO. 6=
     Alternating Current Motors, Transformers, Converters, Rectifiers.

=ELECTRICAL GUIDE, NO. 7=
     Alternating Current Systems, Circuit Breakers, Measuring
   Instruments.

=ELECTRICAL GUIDE, NO. 8=
     Alternating Current Switch Boards, Wiring, Power Stations,
   Installation and Operation.

=ELECTRICAL GUIDE, NO. 9=
     Telephone, Telegraph, Wireless, Bells, Lighting, Railways.

=ELECTRICAL GUIDE, NO. 10=
     Modern Practical Applications of Electricity and Ready Reference
   Index of the 10 Numbers.

  =Theo. Audel & Co., Publishers.     72 FIFTH AVENUE=,
                                        =NEW YORK.=





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