STANDARDIZATION RULES OF Till: 17 



h FORM-FACTOR OF AN ALTERNATING WAVE. The ratio of the root 



square to the arithmetical mean ordinate of a wave, taken without regard to 

 sign, is called its form-factor. The form-factor for a purely rectangular 

 wave is the minimum, 1.0; for a sine wave it is 1.11, and for a 

 more peaked than a sine wave it is greater than 111 



6i THE EQUIVALENT SINE WAVE is a sine wave having the same frequency 

 and the same r.m.s value as the actual wave. 



.e DEVIATION of wave-form from the sinusoidal is determined py super- 

 posing upon the actual wave, (as determined by oscillograph), the equiva- 

 lent sine wave of equal length, in such a manner as to give the least <lif 

 ference, and then dividing the maximum difference between corresponding 

 ordinates by the maximum value of the equivalent sine wave. 



6k PHASE DIFFERENCE. When corresponding cyclic values of two sinu- 

 soidal alternating quantities such as two alternating currents or e.m.fs. or 

 of a current and an e.m.f ., of the same frequency, occur at different instants, 

 the two alternating quantities are said to differ in phase, their phase dif- 

 ference being the time interval, expressed in degrees or as a fraction of a 

 cycle, between the occurrence of their corresponding values; e.g. their 

 ascending zeros or their positive maxima. 



61 EQUIVALENT PHASE DIFFERENCE. If two alternating quantities are 

 non-sinusoidal, and of different wave shapes, the preceding definition of 

 phase-difference is inapplicable, and phase-difference ceases to have exact 

 significance. However, when the two complex alternating quantities 

 are the voltage E and current / in a given circuit, the effective power P of 

 which is known, it is customary to define the equivalent phase difference 

 by the angle whose cosine is the power-factor, P/EI, of the circuit. See 

 Sections 54 and :VJ \ . 



6m SINGLE-PHASE. A term characterizing a simple alternating current 

 circuit energized by a single alternating e.m.f. Such a circuit is usually 

 supplied through two wires. The currents in these two wires counted 

 positively outwards from the source, differ in phase by 180 degrees or half 

 a cycle. 



6n THREE-PHASE. A term characterizing the combination of three circuits 

 energized by alternating e.m.fs. which differ in phase by one third of a cycle; 

 i.e.. 120. 



60 QUARTER-PHASE, also called TWO-PHASE. A term characterizing the 

 combination of two circuits energized by alternating e.m.fs. which differ 

 in phase by a quarter of a cycle; i.e., 90. 



6p SIX-PHASE. A term characterizing the combination of six circuits ener- 

 gized by alternating e.m.fs. which differ in phase by one sixth of a cycle; 

 60*. 



6q POLYPHASE is the general term applied to any alternating system with 

 more than a single phase. 



6 An OSCILLATING CURRENT is a current alternating in direction, and of 

 decreasing amplit 



" 



H. DEFINITIONS. ROTATING MACHINES. 



7 A GENERATOR transforms mechanical power into electrical power. 



8 A DIRECT-CURRENT GENERATOR produces a direct current that may or 

 may not be continuous. 



9 An ALTERNATOR is an alternating-current generator, either single-phase 

 or polyphase. 



9a A SYNCHRONOUS ALTERNATOR comprises a constant magnetic field and 

 an armature delivering either single-phase or polyphase current in syn- 

 chronism with the rotation of the machine. 



10 A POLYPHASE GENERATOR produces currents differing symmetrically 

 in phase; such as quarter-phase currents, in which the terminal voltages of 

 th* two circuits differ in phase by 90 degrees; or three-phase currents, in 

 which the terminal voltages of the three circuits differ in phase by 120 

 degrees. 



