GENERAL THEORY OF THE INDUCTION MOTOR. 277 



f-f 



appears as electrical power in the rotor windings.* Therefore 

 the total power delivered to the rotor, the mechanical power devel- 

 oped in the rotor, and the electrical power developed in the rotor are 

 to each other as n : n' : n n f , or as I : i s : s. 



Equivalent transformer action of the induction motor. If an 

 induction motor is running at a given slip (with a given load), 

 then the rotor electromotive forces, the rotor currents, and the 

 magnetic flux 4>' which enters the rotor from a polar region of 

 the stator all have definite values, although the flux <!>' is less 

 than the flux <I> which leaves a stator pole, on account of mag- 

 netic leakage. However, the difference between <E> and <>' 

 depends only upon the values of stator and rotor currents. This 

 may be seen from Fig. 24 1 , 

 inasmuch as the leakage 

 flux <l> <>' which passes 

 between the stator and rotor 

 windings may be thought 

 of as produced by the 

 down-flowing currents in 

 the A conductors and the 

 up-flowing currents in the 

 B conductors. The stator 

 and rotor conductors are 

 shown as covering only a 

 portion of the periphery 

 in Fig. 24 1 for the sake of clearness. 



Now, suppose that the rotor is brought to a standstill (slip = 

 unity), and suppose that the flux <' remains unchanged in value, 

 then the electromotive forces induced in the rotor windings would 

 be increased in proportion to the increase of slip (s : i) and, if the 

 resistance of the rotor windings were increased in the same ratio, 

 the rotor currents would be the same as before, and <' would in 

 fact be unchanged. 



* This ignores the eddy current and hysteresis losses in the rotor iron, and these 

 losses are usually quite small because of the low frequency of the reversals of the 

 magnetism of the rotor iron. 



Fig. 241. 



