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GATE 2016 EE – Question 26

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

In a constant V/f induction motor drive, the slip at the maximum torque

  1. is directly proportional to the synchronous speed.
  2. remains constant with respect to the synchronous speed.
  3. has an inverse relation with the synchronous speed.
  4. has no relation with the synchronous speed.

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Show answer and explanation

Correct answer: (C) has an inverse relation with the synchronous speed.

Explanation

The slip at maximum torque is $s_m = \frac{R_2'}{X_2'}$, and the leakage reactance $X_2'$ is proportional to the supply frequency, which is proportional to the synchronous speed. So $s_m$ is inversely proportional to the synchronous speed.