Class 4 (4th Engineer) MET 📅 Dec 2022

Exam Question

(a) Explain why it is necessary to have reverse power protection for alternators intended for parallel operation. (8)

(b) (i) Sketch a reverse power trip. (4)

(ii) Explain briefly the principle on which the operation of this power trip is based and how tripping is activated. (4)

Reference Answer

### (a) Necessity for Reverse Power Protection
Reverse power protection is a mandatory safety feature for any alternator intended to operate in parallel with others. Its primary function is to detect a condition where an alternator stops supplying power to the busbars and instead starts consuming power from them, a phenomenon known as 'motoring'. This condition occurs almost exclusively due to the failure of the alternator's prime mover (e.g., a diesel engine).
The reasons for its necessity are critical for the safety and integrity of the machinery and the ship's power plant:
1. **Protection of the Prime Mover:** This is the most critical reason.

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