SYNCHRONOUS MACHINERY 



227 



is the revolving part of the magnetic circuit and is called the in- 

 ductor. The polar projections on it are all north poles but the 

 amount of flux issuing from I and linking with the armature 

 coils a,a, b,b, depends on the relative position of the inductor 

 projections and the projections carrying the armature coils. 



In Fig. 194, curve 1 represents the variation of the flux cj> a 

 interlinking with one armature coil a starting from the position 

 when this flux is maximum, Fig. 193. Curve 2 represents the 

 e.m.f. generated in coil a by the varying flux. As <f> a decreases 



FIG. 194. Fluxes and e.m.f. 's in an inductor alternator. 



an e.m.f. is generated in the positive direction and as it increases 

 again an e.m.f. is generated in the negative direction. Thus al- 

 though the flux does not reverse its direction and never reaches 

 zero, an alternating e.m.f. is generated in the armature coil. 

 If the pole pieces are properly shaped a sine wave of e.m.f. will 

 be produced. Curves 3 and 4 represent the variation of flux 

 and e.m.f. in coil b. The e.m.f. in coil b is displaced 180 degrees 

 from that in a and before the two are connected in series the 

 terminals of one must be reversed. 



Inductor alternators were very heavy and expensive and have 

 been superseded by the other types. 



Any one of these three types may be wound as single-phase or 

 polyphase machines. 



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