THE INDUCTION MOTOR. 



377 



its full periodicity. Under normal running conditions 

 the iron losses in the rotor core are small because the 

 frequency of rotation of the magnetic field relative to the 

 core is only the frequency of the slip and not of the 

 supply current. 



The total amount of the iron losses will, of course, be 

 small, because the maximum voltage applied during the 

 experiment was only about one-fourth of the working 

 voltage. 



In the conditions under which the curves shown in 

 Fig. 183 were taken, viz., with stationary rotor, the motor 

 is practically a static transformer, the stator and rotor 



30 



20 



10 



10 



40 



50 



20 30 



Rotor Amperes. 



Fiu. 184. RATIO OF CURRKNTS. 

 Full line = Full voltage, motor running under load. 

 Dotted line= Motor clamped, voltage varied. 



forming the primary and secondary windings. The test 

 is consequently similar to the curve taken on a short- 

 circuited transformer in order to separate the copper 

 losses (see Fig. 70, p. 153). 



It will be noticed on comparing the two curves 

 that the shape of the watts curve, showing the copper 

 losses, is similar in the two cases. 



The current curves are straight lines. In the case of 

 the rotor this is easy to understand, since the current 

 will naturally increase in proportion to the increased 

 voltage induced in it by the transformer action. The 

 primary current increases in proportion to the secondary 

 current, as in a transformer, in order to counteract the 



