252 



ELEMENTS OF ELECTRICAL ENGINEERING. 



short-circuiting rings of copper. Figure 223 shows a complete 

 three-phase induction motor, the three wires for supplying the 



Fig. 219. Fig. 220. 



three-phase currents to the stator are shown at the lower left- 

 hand side in the figure. 



In some cases, especially for induction motors of large size, 

 the rotor is wound like a polyphase alternator armature,. and the 

 winding is short-circuited through an adjustable resistance. Thus 



Fig. 221. Fig. 222. 



Fig. 224 shows a wire- wound rotor with a device in its interior 

 for varying the short-circuit resistance of the windings ; the resist- 

 ance is usually controlled by pushing on a knob at the end of the 

 rotor shaft. In Fig. 224 the resistance is controlled by a lever 

 (not shown in the figure) which engages the ring-like projection 

 on the short sleeve. Figure 225 shows a wire-wound rotor with 

 the terminals of the winding brought out to three collector rings 

 through which the windings may be connected to an external 



