Class 2 (2nd Engineer) MET 📅 Nov 2024

Exam Question

With reference to preferential tripping in a marine electrical distribution system:

(a) State why this facility is required. (6)

(b) With the aid of a sketch, describe a typical arrangement to provide three stages of tripping an instantaneous protection against short circuit. (10)

Reference Answer

(a) Why Preferential tripping is required:
In marine electrical systems, continuous power supply to the switchboard is essential to maintain vessel safety. A blackout resulting from the tripping of the alternator breaker can compromise the vessel’s operation and safety.
The preferential tripping system ensures that the alternator breaker only trips instantly in the event of a severe fault like a short circuit.
For less severe overcurrent conditions (e.g., 110% of full load), time-delayed relays perform preferential tripping by shedding non-essential loads such as galley equipment, air conditioning, and ventilation fans.

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