370 Electrical Power Systems Technology
Since the stator polarity changes in step with the applied AC, it de-
velops a rotating magnetic field. The rotor becomes instantaneously polar-
ized, as the result of the induced current flow through the short-circuited
copper conductors. The rotor will, therefore, tend to rotate in step with the
revolving magnetic field of the stator. If some method of initially starting
rotation is used, the rotor will continue to rotate. However, because of in-
ertia, a rotor must be put into motion initially by some auxiliary method.
It should be pointed out that the speed of an AC induction motor is
dependent on the speed of the rotating magnetic field and the number of
stator poles that the motor has. The speed of the rotor will never be as high
as the speed of the rotating stator field. If the two speeds were equal, there
Figure 14-15. Illustration of the induction principle: (A) Pictorial diagram, (8)
Squirrel-cage rotor