350 ELECTRICAL ENGINEERING 



The torque in synchronous watts was found in Art. 213 to be 

 equal to the rotor input in watts which is 



' ' (329) 



P r = nE 2 h cos 6 2 



= nE' X #'ai = nE' 2 ai 



where n is the number of phases. 



The rotor output neglecting friction losses is 



p = (i - 8 ) p r 



37*2 (1 s) 



+ * ) (r 



/oom 



The stator power factor is cos 0i, where 0i is the angle of lag of 

 the current /i behind the impressed e.m.f. EI. 0i = 6' + 0", 



cos0' = Cl and cos0" = = J 



therefore 



cos 0i = cos (0' + 0") = cos 0' cos 0" - sin 0' sin 0" 



The power input to the stator is 

 PI = n#i/i cos 0i 



c 2 



/QQ1\ 



Using these equations the various quantities can be calculated 

 in terms of the slip and the characteristic curves of the motor 

 plotted. 



222. Single-phase Induction Motor. The stator of a single- 

 phase induction motor has a single winding with any number of 

 pairs of poles. 



The rotor is either of the squirrel-cage type or is wound with 

 the same number of poles as the stator but with any number of 

 phases. 



