Question

A 14-pole, 3-phase, 50 Hz induction motor is operating at a speed of 99 rpm. The frequency of the rotor current of the motor in Hz is __________

(a) 39.5

(b) 40

(c) 38.45

(d) 39.9

The question was asked in quiz.

Enquiry is from Starting topic in portion Starting of Electric Drives

Answer 1

The correct option is (c) 38.45

Explanation: Given a number of poles = 14. Supply frequency is 50 Hz. Rotor speed is 699 rpm. Ns=120×f÷P=120×50÷14 = 428.57 rpm. S=Ns-Nr÷Ns=428.57-99÷428.57=.769. F2=sf=.769×50=38.45 Hz.