Class 4 (4th Engineer) MET 📅 Apr 2025

Exam Question

(a) Explain why it is necessary to have reverse power protection for alternators intended for parallel operation. (6)

(b) (i) Sketch a reverse power trip. (5)

(ii) Explain briefly the principle on which the operation of this power trip is based and how tripping is activated. (5)

Reference Answer

### (a) Necessity of Reverse Power Protection
Reverse power protection is a critical safety and operational requirement for alternators intended for parallel operation. A reverse power condition, or 'motoring', occurs when an alternator ceases to deliver active power (kW) to the busbars and instead starts consuming power from them, acting as a synchronous motor.
The necessity for this protection arises from the severe consequences for both the prime mover and the electrical system:
**1. Consequences for the Prime Mover (Diesel Engine):**

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