INDUCTION MOTOR 



325 



201. The Stator. The primary or stator consists of a winding 

 carried in slots on the inner face of a laminated iron core. The 

 winding is similar to an alternator or synchronous motor winding 

 and the coils are connected in groups according to the number of 

 phases and poles, one group per phase per pair of poles. 



The stator is supplied with polyphase alternating currents and 

 a revolving m.m.f. is produced similar to the m.m.f. of armature 

 reaction in an alternator, which produces a magnetic field re- 

 volving at a constant speed called the synchronous speed of the 

 motor. 



In Fig. 308 (a) represents the stator winding of a two-pole, 



Phase . ii=Io Cos 

 Current J . Phase 2,i]=Ib Sin Q 



(4) 



FIG. 308. Revolving m.m.f. and flux in a two-pole, two- 

 phase induction motor. 



two-phase induction motor, (6) the currents supplied to the two 

 phases and (c) the fluxes produced by the resultant stator m.m.f. 

 at the points (1), (2), (3) and (4) of the cycle. 



The windings start at Si and s z and finish at /i and / 2 , respec- 

 tively. A positive current is one which enters at Si or Sz and a 

 negative current is one which enters at/i or/ 2 . 



Referring to Fig. 308 (c) it is seen that the north pole makes one 

 complete revolution in the anti-clockwise direction while the 

 current in phase 1 passed through one cycle. 



Fig. 309 (a) represents the stator of a two-pole three-phase 



