Question

A 3-phase induction motor has full load efficiency of 0.7 and a maximum efficiency of 0.85. It is operated at a slip of 0.6 by reduced voltage method. The efficiency of the motor at this operating point is?

(a) less than 0.35

(b) greater than 0.35

(c) in the range of 0.8 to 0.2

(d) none of the mentioned

The question was posed to me in quiz.

This interesting question is from Induction Generator in chapter Induction Machines of Electrical Machines

Answer 1

Right answer is (a) less than 0.35

The best explanation: For the slip more than 40%, the efficiency reduces more than 50% for an induction motor.