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A 4-pole, 3-phase, 60 Hz induction motor is operating at a speed of 1500 rpm. The frequency of the rotor current of the motor in Hz is __________(a) 5(b) 4(c) 2(d) 7This question was addressed to me during an interview.My question is taken from DC Motors topic in section Characteristics of DC & AC Motors of Electric Drives

Answer»

Correct choice is (b) 4

To explain I would say: Given a NUMBER of POLES = 4. SUPPLY frequency is 60 Hz. Rotor SPEED is 1500 rpm. Ns = 120×f÷P = 120×60÷4 = 1800 rpm. S=Ns-Nr÷Ns = 1800-1500÷1800 = .166. F2=sf=.166×60=4 Hz.



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