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GATE 2024 EE – Question 17

Electrical Machines · Three-phase induction machines: principle of operation, types, performance, torque-speed characteristics, no-load and blocked-rotor tests, equivalent circuit, starting and speed control · 1 mark · Multiple choice

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

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Correct answer: (C) 96

Explanation

$N_s=\dfrac{120\times50}{6}=1000$ rpm, so the slip is $s=\dfrac{1000-960}{1000}=0.04$. With only rotor copper loss, the efficiency is $1-s=0.96$, i.e. 96%.