Page 698 - Basic Electrical Engineering

There is similarity between a transformer and an induction motor. An
induction motor is like a short circuited transformer. This has been shown in
Fig. 8.14. The only difference is that the secondary, i.e., the rotor in an

induction motor is cylindrical in shape and is free to rotate while a
transformer is totally a static device. The secondary winding, i.e., the rotor

winding of an induction motor is closed, i.e., shorted. The similarity between
an induction motor and a short-circuited transformer has been shown in Fig.

8.14 (a and b).
With the secondary winding of a transformer short circuited, if full voltage

is applied across the primary windings, very high current will flow through
the windings. As in the case of transformers, when full voltage applied across
stator terminals of an induction motor and the rotor is stationary, very high

current will flow through the rotor and stator windings. If this high current is
allowed to flow for a considerable time the motor windings will be burnt out.

However, as the motor picks up speed, the EMF induced in it will be SE so
20
that

Figure 8.14 (a) Induction motor; (b) transformer with its secondary windings shorted; (c) high
current drawn by an induction motor if started with full voltage