9.List FIVE safety devices that may be fitted to the main swichboard of a vessel, stating reasons for fitting each device.
(10)
Q9. Five safety devices that may be fitted to the main switchboard of a vessel, with reasons for fitting each (10 marks)
1. Circuit Breakers (Air Circuit Breaker / MCBs)
- Reason: Protect the generators and distribution system against overcurrent and short circuits, disconnecting the faulty circuit to prevent equipment damage or fire.
2. Reverse Power Relay
- Reason: Prevents a generator from becoming a motor and driving the prime mover (e.g. diesel engine or turbine) if synchronisation is lost or if load drops suddenly.
3. Under/Over-Voltage Protection Relay
- Reason: Trips the generator if voltage deviates beyond safe limits, protecting equipment and consumers from damage caused by under-voltage (loss of supply) or over-voltage (insulation breakdown).
4. Under/Over-Frequency Relay
- Reason: Disconnects the generator in the event of abnormal frequency, which may result from governor failure or excessive load, protecting both machinery and sensitive electronic equipment.
5. Earth Fault Indicator/Relay
- Reason: Detects insulation failure and leakage to earth, giving an alarm or tripping to prevent electric shock risk, fire hazard, or progressive insulation breakdown.