198 



ELECTRICAL MACHINERY 



harmonics, being some multiple of the fundamental wave; 

 the 180 cycle is the tnird harmonic of the 60-cycle wave and 

 the 300-cycle wave is the fifth harmonic, etc. 



FIG. 117. A Sine Curve of E.M.F. 



In all ordinary cases of distorted waves only the odd 

 harmonics appear; when a curve has the symmetry men- 

 tioned in the previous paragraph it may at once be assumed 

 that no even harmonics are present. 



FIG. 118. Voltage and Current Forms in an a-c. Circuit having an 

 Iron Core Inductance. 



Typical Wave Shapes. In Figs. 118 and 119 are shown 

 some typical wave forms. Fig. 118 shows an e.m.f. wave 

 of nearly pure sine form. The current wave in the same 



