THE INDUCTION MOTOR. 



259 



flux passes from stator iron into rotor iron the stator iron has north 

 magnetic polarity, and where the flux passes from rotor iron into 

 stator iron the stator iron has south magnetic polarity. The loca- 

 tion of these poles at the given instant is shown by the letters 

 NSNS. 



When the lines A' and B f have rotated ^ of a revolution, 

 as shown in Fig. 230, the current in the A bands has decreased 

 and the current in the B bands has increased, the two currents 

 have become equal in value, and the magnetic flux due to the 

 stator windings has shifted, as indicated by the dotted lines in 

 Fig. 230. 



When the lines A' and B f have rotated J^ of a revolution, 

 as shown in Fig. 231, the current in the A bands has decreased 



up flowing currents 

 Fig. 232. 



down flowing currents 

 Fig. 233. 



to zero, the current in the B bands has increased to its maxi- 

 mum value, and the magnetic flux due to the stator windings has 

 shifted still farther, as indicated by the dotted lines in Fig. 231. 

 As a matter of fact, the magnetic flux due to the stator wind- 

 ings shifts continuously forwards, and by comparing Fig. 229 

 with Fig. 231 it is seen that the forward shift of the polar regions 

 of the stator during j of a cycle (j of a revolution of the 

 clock diagram A f B') is equal to ^ of the distance from N to 

 vS* in Fig. 229. In a whole cycle, therefore, the forward shift 

 of the polar regions is two times the distance from TV to S in 

 Fig. 229 which is equal to the distance from TV to N. That is to 

 say, the stator magnetism makes a complete revolution in //2 

 cycles, where p is the number of polar regions on the stator 

 iron (NS NS in Fig. 229). Therefore, if the alternating cur- 



