ETO ETO Exam papers 📅 Feb 2024

Exam Question

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

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

(b) State why this protection is required. (6)

Reference Answer

(a) Preferential trips operate after a fixed time delay, causing non-essential loads to be shed.
When the generator load reaches 110%, preferential Trip comes into operation as follows
First Stage Preferential Tripping (PT1):
Initiated when the current on a running generator exceeds 100% of the generator rating for a period of 10 seconds.

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