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A 10-pole, 50 Hz, 240 V, single phase induction motor runs at 540 RPM while driving rated load. The frequency of induced rotor currents due to backward field is

1. 100 Hz
2. 95 Hz
3. 10 Hz
4. 5 Hz

Correct answer: 95 Hz

Solution

Synchronous speed Ns=120*50/10=600 rpm, so slip s=(600-540)/600=0.1. The rotor current frequency due to the backward field is (2-s)f=(1.9)(50)=95 Hz.

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