Question

A ship operating in the U.M.S. mode must have an automatic fire detection system for the machinery space.

(a) Sketch a line diagram of the system showing how shipboard mains supply is fed through battery charger and emergency battery to fire detector heads and fire zone indicator panel and alarms.

(b) In the event of a mains supply failure state the length of time for which the emergency battery should be capable of operating the system.

(c) Sketch and describe a line termination or other method of monitoring the integrity of the system.

Answer 1

Part (a)

Line diagram of the system showing shipboard fire detector heads and fire zone indicator panels and alarms supplied by mains and emergency batteries.

Part (b)

In the event of mains supply failure, the emergency battery must be capable of operating the fire detection system for at least 30 minutes

Part (c)

System Integrity monitoring - Line termination and fault detection:

Zone Monitoring (K1, Lamp 1): A normally-closed relay (K1) is energized by the power supply. A closed circuit indicates a functioning zone. If power fails or a break occurs in the circuit for zone A, K1 de-energizes and Lamp 1 extinguishes, indicating a fault.

Overcurrent Detection (K2, Lamp 3): A current sensing device (e.g., a current transformer or overcurrent relay) monitors the total system current. An excessive current, indicating a short circuit or fault, energizes K2 and illuminates Lamp 3.

Leakage Current Detection (K3, Lamp 4): A current transformer (toroid) is placed around the input and return lines of the system. Under normal operation, equal and opposite currents produce no net magnetic flux, thus no current in the secondary winding. A leakage current will result in an imbalance, inducing a current in the secondary winding, energizing K3, and illuminating Lamp 4.

Fire Alarm (K4, Lamp 5): A fire detector head in each zone is a normally open circuit. When a fire occurs, the detector head closes, short-circuiting a known resistance and increasing current. This increased current energizes K4 and illuminates Lamp 5, signalling a fire/smoke alarm in the corresponding zone.

✓ Verified Model Answer (Text Solution)

Line diagram of the system showing shipboard fire detector heads and fire zone indicator panels and alarms supplied by mains and emergency batteries.

In the event of mains supply failure, the emergency battery must be capable of operating the fire detection system for at least 30 minutes

System Integrity monitoring - Line termination and fault detection: