Question With reference to an emergency, source of electrical power in cargo ships:-

Question

With reference to an emergency, source of electrical power in cargo ships:-

(a) Describe a typical power source.

(b) Give a typical list of essential services, which must be supplied simultaneously.

Answer a)

Fig.

Emergency generators for passenger vessels are now required to be automatically started and connected within 45 seconds. A set of automatically connected emergency batteries capable of carrying certain essential items for 30 minutes, is also required.

Alternatively batteries are permitted as the main emergency source of power.

Regulations specify the supply of emergency power to essential services on passenger ships for a period of upto 36 hours.

A shorter period is allowed in vessels such as ferries.

Some of the essential services may be operated by other than electrical means (such as hydraulically controlled water tight doors), others may have their own electrical power.

If the batteries are the only source of power they must supply the emergency load without recharging or excessive voltage drop (12% limit) for the required length of time.

Because the specified period is upto 36 hours: batteries are used normally as a temporary power source with the emergency generator taking over essential supplies when it starts.

The emergency switch board has two sections, one operating at 440 volts and the other at 220 volts.

The 440 V supply, under normal circumstances, is taken from the main engine room switch board through a circuit breaker. A loss of main power causes this breaker to be tripped and the supply is taken over directly by the emergency generator when started through breaker B.

An inter lock prevents simultaneous closure of both breakers.

A special feeder is some times fitted so that in a dead ship situation the emergency generator can be connected to the main switchboard.

This special condition breaker would only be closed when the engine room board was cleared of all load, i.e. all distribution breakers were open. Selected machinery within the capacity of the emergency generator could then be operated to restore power, at which stage the special breaker would be disconnected.

b) Typical essential services include

1) Emergency lighting (at every muster and embarkation station, alleyways, stairways and exits, personnel lift cars, machinery spaces and main generating stations including their control positions, all control stations, emergency switch board all-stowage positions of fireman's outfits, at the steering gear, at the fire pump and the emergency bilge pump and at the starting position of their motors.

2) Navigation lights; and other lights required by COLREG.

3) MF radio installation, ship earth station if applicable.

4) All internal communication equipment required in an emergency.

5) Ship borne navigational equipment.

6) Fire detection and alarm system and fire door holding and release system.

7) Intermittent operation of Day light signaling lamp.

8) The ship's whistle.

9) Manually operated call points.

10) All internal signals that are required in an emergency.

11) One of the fire pumps ( either of the main fire pumps, or the emergency fire pump.)

12) Automatic sprinkler pump,

13) Emergency fire pump. # all the above services for 36Hrs.

Also 14) any water tight doors with their indicators and warning signals

15) The emergency arrangements to bring the lift cars to deck, level for the escape of persons:

c) PERIODICAL TESTING OF THE EMERGENCY INSTALLATION:

Correct functioning of the auto start equipment is obviously vital to the production of emergency power.

Regular, weekly, testing of the emergency generator should include simulation of the loss of normal power.

The start up equipment may provide a pushbutton to interrupt the normal voltage supply to the panel which then triggers the start sequence.

Loss of main power supply can easily be simulated by pulling a fuse in the auto start pane which supplies the under-voltage or under-frequency relay.

Emergency generators should be regularly checked and run up to speed for short test runs to comply with safety regulations. These no-load running checks should when practicable, be supplemented occasionally by a proper load test.

This requires the disconnection of normal mains power while the emergency generator is loaded upto near its rated value. Only the proper load test will prove the performance of the generator and its prime mover, together with its circuit-breaker operation.