THE INDUCTION MOTOR 



227 



It is to be noted that the currents in the disc or armature of this 

 fype of motor are induced therein, rather than being conducted 

 into the armature as in the ordinary direct-current motor. 



A cylinder may be used instead of the disc, as shown in Fig. 218. 

 In the figure are shown four poles, the magnetic lines of 

 which cut the cylinder. If the frame carrying these poles be 

 revolved by mechanical means, the currents induced in the 

 cylinder will cause the cylinder to rotate in the same direction 

 as that of the rotating frame. This cylinder is more representa- 



Direction of 

 rotation of 

 armature wit 

 twipect to Held 



FlO. 218. Rotation ot conductinn cylinder due to induced currents. 



f the connnorci;il induction motor than the* disc is, although 

 both operate on the same principle. 



99. The Alternating-current Rotating Field. The rotating 

 fields described in tin- previous paragraph were produced by 

 rotating the magnetic poles mechanically. This is practically 

 the same as the rotating poles of an alternator field. Rotating 

 tic fields may. however. l>e produced l.y sending polyphase 

 currents through polyphase windings, such as alternator wind- 

 Such rotating fields are produced entirely I >y electrical 



:i iiu 11. d rotation of the p,,l.- : 



themselves. 



