336 ELECTRICAL ENGINEERING 



therefore, 



='(+'4 



if the magnetizing current I M is neglected in comparison with the 

 load component of stator current /'. 



d,k 



/ 



FIG. 318. Induction motor at standstill. 



This value of /' is represented by fk and is the diameter of the 

 circle. Its value is 



^ " T/ El - (302) 



The diameter of the circle, therefore, varies directly as the 

 impressed e.m.f. and inversely as the sum of the reactances and 

 therefore as the frequency of the supply. 



Thus as the motor is loaded the end d of the vector representing 



the stator current follows a semicircle of diameter 



210. Rotor E. M. F. and Current. The e.m.f. generated in 

 one phase of the rotor at slip s by the flux $ g is 



E-ig = sK$ g , where K is a constant, 

 = sE 2 , where E 2 = K$ g is the e.m.f. 



