Question

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

• A. offset Mho relay.
• B. over current relay.
• C. differential relay.
• D. Buchholz relay.

Hint:

The offset Mho relay is used for alternator protection by detecting changes in impedance when excitation is lost.

Answer 1

The Correct Option is A

Step 1: Understanding the Protection Requirement.
The protection of an alternator against loss of excitation is critical to prevent damage due to overheating or mechanical stress. The most effective way to protect an alternator from this issue is by using a relay that detects and responds to the loss of excitation. Step 2: Explanation of the Options.
- (A) offset Mho relay: This is the correct answer. The offset Mho relay is commonly used for alternator protection against loss of excitation, as it detects impedance changes caused by excitation loss.
- (B) over current relay: This is incorrect as over current relays are not specifically designed for loss of excitation protection.
- (C) differential relay: Differential relays are used for the protection of transformers and generators, but they do not specifically protect against loss of excitation.
- (D) Buchholz relay: This is used for transformer protection, not for alternator excitation loss. Step 3: Conclusion.
The correct answer is (A) offset Mho relay, as it is specifically designed to protect against excitation loss in alternators.