Class 4 (4th Engineer) MET 📅 Nov 2025

Exam Question

Overcurrent protection relays are built into main alternator breakers to safeguard the individual alternators and the distribution system against certain faults.

(a) Sketch a typical relay. (8)

(b) Describe the operation of the relay sketched in (a). (8)

Reference Answer

### (a) Sketch of an Attracted Armature Instantaneous Overcurrent Relay
A diagram of an attracted armature type instantaneous overcurrent relay is required. The sketch should clearly label the following essential components:
* **Current Transformer (CT):** Showing the primary connected to the main power line (from the alternator) and the secondary connected to the relay's operating coil.
* **Operating Coil (Relay Coil):** An electromagnet that is energized by the secondary current from the CT.

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