THE INDUCTION MOTOR. 



rent in III. The magnetomotive forces of each phase are represented 

 by the ordinates of the curves I, II, and III respectively. Each ordinate 

 measures the magnetomotive force produced in that place of the cir- 

 cumference in which it is drawn. The adding up of the three curves 

 yields the thick line curve drawn below. 



If the magnetic reluctance is the same at every point of the circum- 

 ference, in other words, if the reluctance of the iron is negligible, 

 then the flux, produced by the magnetomotive force represented by 

 the thick line curve, is proportional to that magnetomotive force. 

 Hence the thick line curve may be taken as "a representation of the 

 flux. We call the total number of lines of induction $, and we as- 



II 



FIG. 8. FIG. Q. 



sume that this flux varies according to a simple sine law. We shall 

 now proceed to calculate the e. m. f. induced by this field upon each 

 phase. 



We have tacitly assumed that the coils I, II, and III are distributed 

 in a practically infinite number of slots. Though this cannot be the 

 case, yet this assumption may safely be made for our present pur- 

 pose. 



19. It is obvious that, if the convolutions of each phase were alj con- 

 centrated in one slot, the effect of the oscillation or the traveling of 



12 



