164 



TREATISE ON ALTERNATING CURRENTS. 



STKUCTURE OF INDUCTION MOTORS. 



112. The stators of all induction motors are built of soft-iron 

 stampings varying from 12 to 20 mils, in thickness. The running 

 coils of monophase induction motors are wound in half-closed 

 slots, which are placed close to the inside periphery, as shown in 

 Fig. 64, while the starting coils are wound in completely closed 

 slots. The stator stampings are built up inside a cast-iron case, 



FIG. 64. 



to which end shields are bolted. The slots are insulated with 

 micanite or other insulating material. In monophase motors there 

 are two distinct windings, one being the running winding always 

 in circuit, the other, the starting winding, in circuit only at start- 

 ing, and whose function is to provide a cross-magnetization, the 

 action of which on the rotor currents produces the starting-torque. 



In di-phase motors there are two similar distinct windings, both 

 of which remain always in circuit. 



In tri-phase motors there are three similar distinct windings, 

 which always remain in circuit. 



RotOPS. The rotors consist of a slotted and laminated core, 



