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A 3-phase induction motor is fed at the stator at a frequency f. If the rotor speed is Nr and synchronous speed is Ns, then the absolute speed of the resultant flux in space is?

(a) Ns

(b) (Ns+Nr) if the flux rotates in the same same direction as the rotor

(c) (Ns-Nr) if the flux rotates in the same same direction as the rotor

(d) Nr

I had been asked this question by my college director while I was bunking the class.

Enquiry is from Starting of Polyphase Induction Motors-II topic in chapter Starting of Induction Motors of Electrical Machines

1 Answer

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Best answer
Correct answer is (a) Ns

Easiest explanation: The flux speed in space will be Ns irrespective of any rotor speed.

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