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GATE 2022 EE – Question 13

Power Systems · Principles of over-current, differential, directional and distance protection; Circuit breakers · 1 mark · Multiple choice

The most commonly used relay, for the protection of an alternator against loss of excitation, is

  1. offset Mho relay.
  2. over current relay.
  3. differential relay.
  4. Buchholz relay.

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Show answer and explanation

Correct answer: (A) offset Mho relay.

Explanation

On loss of excitation the alternator's impedance seen from its terminals moves into the fourth quadrant of the R-X plane, and this is detected by an offset Mho (distance-type) relay. Over-current and differential relays do not sense it, and the Buchholz relay is for transformers.