CHAPTER X 

 THE INDUCTION MOTOR 



89. General Construction. An induction motor, like 

 any other motor, consists of a stationary part and a revolv- 

 ing part. The stationary part is called the stator and the 

 revolving part the rotor. The motor derives its name 

 from the fact that the rotor is not connected electrically to 

 the source of power supply; whatever currents circulate in 

 the rotor conductors are not produced directly by the 

 e.m.f. of the power supply, but result from e.m.fs. induced 

 in the rotor by the action of the magnetic field set up by the 

 stator. 



Principle of Operation. The principle of operation of the 

 induction motor is just the same as that of any other type 

 of motor; the rotating member (rotor) is fitted with a set of 

 conductors. in which currents flow and, as these conductors 

 lie in the magnetic field produced by the stationary part 

 (stator), a force is exerted on the conductors and the rotor 

 tends to revolve. 



The motor depends, for its operation, upon the genera- 

 tion of a rotating magnetic field and the first characteristic 

 of the motor to be examined is this rotating magnetic field. 



90. Rotating Magnetic Field. A picture of the stator 

 of a small induction motor with its windings, is given in 

 Fig. 215. From this .illustration it may be seen that the 

 stator coils are distributed over the inside surface of a 

 laminated iron core. The coils are of few turns and resemble 

 very much the coils for the armature of a c-c. generator. 

 In fact the stator winding resembles very much the armature 



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