302 



ELECTRICAL EQUIPMENT 



Complex alternating current waves as mentioned above can 

 be represented by their equivalent sine wave, having the same 

 effect as the complex wave. They have the same effective value, 

 that is, the same square root of mean square of the instantaneous 

 values of the complex wave. Thus, considering all complex 

 alternating currents as represented by equivalent sine waves, all 

 investigations become applicable to any alternating current cir- 

 cuit irrespective of the wave shape. Terms such as reactance, 

 impedance, etc., are based on the assumption of a sine wave or 

 equivalent sine wave. 



The objections to higher harmonics are, among other things, 

 their effect in increasing the maximum value of the e.m.f. and 



Negative 3rd 

 Harmonic 



FIG. 179. Symmetrical Distorted E.M.F. Waves. 



the correspondingly increased insulation strain, as shown by the 

 peaked waves in Fig. 179. In certain cases the triple frequency 

 voltage established by the generator is of sufficient value to cause 

 heavy triple frequency currents to circulate. A considerable 

 distortion of wave shape might also affect the performance of 

 induction or synchronous motors. Here, if the distortion of the 

 voltage wave acting at the motor terminals is considerable, the 

 rotating field produced will be more or less of a pulsating charac- 

 ter. Induction motors might operate uneconomically with a pos- 

 sibility of dead points in the starting torque, or with a considerable 

 counter torque during running. Synchronous motors or con- 

 verters may hunt, or even fall out of step. Or if the wave shape 



