Question

A 10-pole, 3-phase, 60 Hz induction motor is operating at a speed of 100 rpm. The frequency of the rotor current of the motor in Hz is __________

(a) 52.4

(b) 54.8

(c) 51.66

(d) 51.77

I had been asked this question in semester exam.

The above asked question is from Methods of Starting Electric Motors topic in division Starting of Electric Drives

Answer 1

Correct answer is (c) 51.66

The explanation: Given a number of poles = 10. Supply frequency is 60 Hz. Rotor speed is 100 rpm. Ns = 120×f÷P=120×60÷10 = 720 rpm. S=Ns-Nr÷Ns = 720-100÷720=.86. F2=sf=.86×60=51.66 Hz.