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3d. Induction motors: 25 per cent for one-half hour, 50 per cent for one minute.
4th. Synchronous converters: 50 per cent for one-half hour.
5th. Transformers: 25 per cent for one-half hour; except in transformers connected to apparatus for which a different overload is guaranteed, in which case the same guaranties shall apply for the transformers as for the apparatus connected thereto.
6th. Exciters of alternators and other synchronous machines, 10 per cent more overload than is required for the excitation of the synchronous machine at its guaranteed overload and for the same period of time.
Efficiency of Phase-Displacing Apparatus. —
In apparatus producing phase displacement, as, for example, synchro. nous compensators, exciters of induction generators, reactive coils, condensers,
olarization cells, etc., the efficiency should be understood to be the ratio of the volt-ampere activity to the volt-ampere activity plus power loss.
The efficiency may be calculated by determining the losses individually, adding to them the volt-ampere activity, and then dividing the volt-ampere activity by the sum.
1st. In synchronous compensators and exciters of induction generators, the determination of losses is the same as in other synchronous machines under Sections 10 and 11.
2d. In reactive coils the losses are molecular friction, eddy losses, and 1 ? r loss. They should be measured by wattmeter. The efficiency of reactive coils should be determined with a sine wave of impressed E.M.F., except where expressly specified otherwise.
3d. In condensers, the losses are due to dielectric hysteresis and leakage, and should be determined by wattmeter with a sine wave of E.M.F.
4th. In polarization cells, the losses are those due to electric resistivity and a loss in the electrolyte of the nature of chemical hysteresis, and are usually very considerable. They depend upon the frequency, voltage, and temperature, and should be determined with a sine wave of impressed E.M.F., except where expressly specified otherwise.
APPENDIX II. Apparent Efficiency.
In apparatus in which a phase displacement is inherent to their operation, apparent efficiency should be understood as the ratio of net power output to volt-ampere input.
Such apparatus comprise induction motors, reactive synchronous converters, synchronous converters controlling the voltage of an alternating-cur. rent system, self-exciting synchronous motors, potential regulators, and open magnetic circuit transformers, etc.
Since the apparent efficiency of apparatus generating electric power depends upon the power factor of the load, the apparent efficiency, unless otherwise specified, should be referred to a load power-factor of unity.
APPENDIX III, Power Factor and Inductance Factor. –
The power factor in alternating circuits or apparatus may be defined as the ratio of the electric power, in watts, to volt-amperes.
The inductance factor is to be considered as the ratio of wattless voltamperes to total volt-amperes. Thus, if p = power factor, a = inductance factor,
p2 +q2 = 1.
(energy component of current or E.M.F.) The power factor is the le
(total current or E.M.F. and the inductance factor is the
(wattless component of current or E.M.F. - true power.
volt amperes. Since the power-factor of apparatus supplying electric power depends upon the power-factor of the load, the power-factor of the load should be considered as unity, unless otherwise specified.
APPENDIX V. Table of Sparking Distances in Air between Opposed Sharp NeedlePoints, for Various Effective Sinusoidal Voltages, in inches and in centimeters.
KILOVOLTS SQ. RooT OF
11.8 14.9 18.0 21.2 24.4 27.3 30.1 32.9 35.4 38.1
Cables for Electric Lighting ...... 281
. . . 155
Concentric . . . . . . . . . . 284
. . .2
. . 112
Of Cables and Conductors ...
Effect on Current . · · · · ·
Formulas for .......
Wave, Form of .... . . . 112 Cardew Earthing Device .....
Circuit-breakers . .......
. .. 389
. . . 57
297 Cleats ............
. . . . 376
.. . 329 Compound Dynamos, Regulation by.
Compensator for Voltmeter. ...... 199
346 Compensated Field Alternator ...... 195
Conductors, Current Capacity and Table , 13, 15
Design and Economy in ... 10, 87, 226
Measurement of ......... 1
Materials for .......... 3
Coefficient of Change of Resistance
Losses in Transformers . .
Conductors, Economy in ...
Constant Potential Regulator ......
Current Transformer . .
Conduit, Cast Iron . . . . . .
. . . . 273
Edison Tube System . .
Converter, Rotary . .
Cooling of Transformers . . .
Crompton System .....
Alternating Current Systems of . 186 to 223
. . . . . 93
D. C. Transformers .......93
Polyphase Systems of ....... 200
Single-phase Systems of ......
Table of .....
Induction Motor ......
Induction, Self and Mutual. ..
Insulation . . . . . . . . .
Interior ( onduit . ......
Iron Losses in Transiormers . . . . . . 134
Joints in Cables ...
in Line Wires ..
All Day, Table .......... 113 Knob and Tube Wiring ........ 378
Lag Due to Inductance......
Leakage, Magnetic in Transformers ...
Magnetizing Currents in Transformers
Magnetic Leakage in Transformers ....
Mains, Calculation of ......38
Mains and Taps . . . . . . . · · · *85
. . . . . . . 86
Manholes . . . . . . . . . . . . . 286
Matthiessen's Standard of Conductivity .. 6
Mesh Connection. See Delta.
Motor-Converter .......... 93
as Compensators ...
Motor, Induction .....
Synchronous · · · · ·
Transformer . . . .
Municipal Lighting Circuits . . . . . .
Mutual Induction . . . . . . . . .15, 134
Inductance of Circuits ....... 131
Naked Conductor Underground Systems . 279
Networks of Conductors ....... 103
Current and Drop in. ....... 103
Design of ............ 106
Neutral Conductor, Grounding of . 84 and App. I
Impedance . . . . . . . . . . . 131
of Parallel Circuits ....... 126
of Series Circuits . . . . . . . . . 126
Globes . . . . . . . . . . . 399
Life . . . . . . . . . .
Over-Compound dynamos, regulation by . 53
Insulators for .......... 248
. . . . . 243
| Panel Board ............
Regulation of ...........