CHAPTER XIV 

 DETERMINATION OF WAVE FORM 



To simplify the mathematical treatment of the flow of alternat- 

 ing currents, it is customary to assume that both the applied 

 e.m.f. wave and the current wave are sinusoidal. 



Designers now aim to produce machines with e.m.f. waves 

 which are sinsuoidal, or nearly so, since experience has shown 

 that, all things considered, this form of e.m.f. wave is the most 

 advantageous in practice. As an illustration, modern metering 

 devices, upon whose indications the charges for electric service 

 are based, will not give results which are commercially correct 

 if the wave form is badly distorted so that it differs reatly from 

 a sinusoid. 



/ V \ 



A 

 FIG. 376. Examples of wave forms. 



Fig. 376, A, shows the e.m.f. wave of a modern turbo-alternator. \ 

 The departure from the sinusoidal form is not obvious and a care- 

 ful analysis must be made before one can state what^t is. On 

 the other hand, Fig. 376, 5, shows the e.m.f. wave of a much older 

 type of machine ; such a wave form might seriously complicate the 

 behavior of the devices placed in circuit. 



The form of the current wave is affected by the character of 

 the circuit. If the e.m.f. wave is not a pure sine curve, the effect 

 of its various harmonics in the current wave will be accentuated 

 by capacity and smoothed out by inductance in the circuit. 



Saturation effects in iron cores may also materially affect 

 the form of the current wave. This is illustrated in Fig. 377, 



612 



