Question

An Induction Motor is expected to run at 950 rpm at full load. With a power supply of 50 Hz. What could be the number of poles in the IM?
1. four
2. Six
3. Eight
4. Two

Answer 1

Correct Answer - Option 2 : Six

Concept:

An induction motor works on the principle of electromagnetic induction. It is possible, only when there is a relative speed between the rotor, and synchronously rotating armature flux.

So, the rotor of an induction motor runs at a speed, less than its synchronous speed. The difference speed the rotor speed and the synchronous speed is called slip speed.

The synchronous speed of an induction motor is given by

\({N_s} = \frac{{120f}}{P}\)

Where f is the supply frequency

P is the number of poles

Calculation:

Given that, the speed of the induction motor (N_r) = 950 rpm

The synchronous speed (N_s) = 1000 rpm

Frequency (f) = 50 Hz

\({N_s} = \frac{{120 \times 50}}{P} = 1000\)

⇒ P = 6