INDUCTION MOTOR 



327 



induction motor, 309(6) the currents supplied and 309 (c) the 

 fluxes corresponding to the points (1), (2), (3) and (4) on the 

 cycle. The north pole as before makes one revolution during 

 one cycle. 



Fig. 310(a) represents the stator of a four-pole, two-phase 

 induction motor, (6) the currents supplied and (c) the fluxes 

 produced. 



Fig. 311 (a), (6) and (c) represent a similar set of conditions 

 for a four-pole, three-phase stator. 



(4) 



FIG. 311. Revolving m.m.f. and flux in a four-pole, three- 

 phase induction motor. 



In Fig. 310(c) and Fig. 311(c) it is seen that, while the current 

 goes through one cycle, the revolving field turns through the angle 

 occupied by one pair of poles. 



If the stator winding has p-poles, the revolving field turns 



through 



degrees, that is, through - of one revolution during 



one cycle of the current. 



If the frequency of the supply is / cycles per second the revolving 



2 f ^20 f 



field makes r.p.s. or - r.p.m. The synchronous speed of an 



induction motor is, therefore, 



A7 120 / 



N = r.p.m. 



P 



(300) 



