The GATE Grind

GATE 2023 EE – Question 16

Electrical Machines · Operating principle of single-phase induction motors · 1 mark · Multiple choice

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

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Correct answer: (B) 95 Hz

Explanation

$N_s=\dfrac{120\times50}{10}=600$ rpm, so the forward slip is $s=\dfrac{600-540}{600}=0.1$. The slip with respect to the backward field is $2-s=1.9$, so the rotor current frequency is $1.9\times50=95$ Hz.