Question

The stator of a 3-phase induction motor has 2 slots per pole per phase. If supply frequency is 50 Hz, then calculate the number of stator poles and total number of slots on the stator.
1. 8 poles, 36 slots
2. 4 poles, 24 slots
3. 8 poles, 92 slots
4. 6 poles, 54 slots

Answer 1

Correct Answer - Option 2 : 4 poles, 24 slots

Concept:

Synchronous speed:

It is the speed of rotation of magnetic field with respect to apparatus on which the coil is wound. Suppose, supply is given to the stator then rotating magnetic field produced will have synchronous speed with respect to stator. Similarly, if supply is given to the rotor then rotating magnetic field produced will have synchronous speed with respect to the rotor.

\(N_s= \frac{120 × f}{P}\)

where, N_s = Synchronous speed

f = Supply frequency

P = Number of poles.

Calculation:

Give, Slots per pole per phase = 2

i.e. \(\rm \frac{slots}{pole × phase} = 2\)

∵ phase = 3

∴ \(\frac{slots}{pole} = 2 × 3 = 6\)

Considering, Number of poles = 4

then, no. of slots = 6 × 4 = 24

Therefore, the current option is (2)

Note:

It is an official question of DFCCIL executive trainee paper, as per the official paper option 1 is 6 poles and 36 slots, if that is the case both option 1, and Option 2 are correct, for that reason we have changed option 1.