Page 712 - Basic Electrical Engineering

Substituting values

or, N = 960 rpm
r

Example 8.5 A slip-ring-type three-phase induction motor rotates at a

speed of 1440 rpm when a 400 V, 50 Hz is applied across the stator
terminals. What will be the frequency of the rotor-induced EMF?

Solution:

We know the synchronous speed of the rotating magnetic field produced is
expressed as

Here, f = 50 Hz but number of poles of the stator winding has not been
mentioned. The number of poles can be 2, 4, 6, 8, etc.

for

for

for

for

We know that an induction motor runs at a speed slightly less than the

synchronous speed. Here, N = 1440 rpm (given). Synchronous speed
r