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A three phase, 50 Hz, 6 pole induction motor runs at 960 rpm. The stator copper loss, core loss, and the rotational loss of the motor can be neglected. The percentage efficiency of the motor is

1. 92
2. 94
3. 96
4. 98

Correct answer: 96

Solution

Ns=120*50/6=1000 rpm, so slip s=(1000-960)/1000=0.04. With stator copper, core, and rotational losses neglected, efficiency equals (1-s)=0.96, i.e. 96%.

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