332 



ELECTRICAL ENGINEERING 



= sN r.p.m. But the rotor itself is revolving at a speed 



S = (1 s) N r.p.m. and therefore the rotor m.m.f . is revolving 

 at a speed sN + (1 s) N = N, that is, at the same speed as 

 the stator m.m.f. The two m.m.fs. are therefore stationary rela- 

 tive to each other and they are nearly opposite in phase as in the 

 transformer. 



206. E. M. F. and Flux Diagram for the Induction Motor. 

 Let 7*1 = stator resistance per phase. 



J/i = stator self-inductance per phase. 



Xi = 2 TT/I/i = stator reactance per phase. 



Zi = V ri 2 + Xi 2 = stator impedance per phase. 



7*2 = rotor resistance per phase. 



Lz = rotor self-inductance per phase. 



#2 = 2 71/1/2 = rotor reactance per phase at standstill. 

 sxz = 2 7TS/I/2 = rotor reactance per phase at slip s. 



Zz = vV 2 2 + x 2 2 = rotor impedance per phase at standstill. 



Zz = Vr 2 2 + s 2 Xz 2 = rotor impedance per phase at slip s. 



FIG. 315. Flux and e.m.f. diagram of an induction motor. 



In Fig. 315 



EI = the e.m.f. impressed on one phase of the stator. 

 7i = the current in one phase of the stator. 7i = I M +/'. 

 IM = the magnetizing current in one phase of the stator. 

 /'_= the load current in one phase of the stator. 



