Electrical Maintenance And Earth Fault On Ships

Scheduled and routine maintenance is the key to ensure smooth running of electrical machinery systems and to prevent hazardous accidents on board ships. Earth fault is considered very critical on board a ship. Some ships, which operate at 440V do not have any trip devices attached for a single earth fault. However, when the operating voltage exceeds 3000V, it is mandatory to have a protection system that isolates when ship machinery suffers an earth fault.

The seriousness of the action to be taken on an Earth Fault depends on the part of the electrical system it affects. Conventional ships which operate on 3 Phase, 440V, have earth fault indicators installed on all three phases. Any earth fault on a 440V system is considered to be a serious trouble and immediate action is required to identify the faulty circuit. Earth fault on 220V or any low voltage lighting circuit can be considered as important but need not require immediate attention. However, attention should be paid at the next earliest opportunity.

Finding Earth Fault on 440V circuit

Whenever there is an earth fault alarm, immediately inform the electrical officer (if he is on board). First action is to check the trueness of the alarm. Usually there will be a test button which when pressed, resets the alarm and rechecks the condition of the earth fault.

If the ship is having IAS (Integrated Automation System), check on the computer in the list of events, after which the alarm has activated. If IAS facility is not available, there is only one option left i.e. isolating each and every machinery system in the 440 V circuit.

When this is done, check for which machinery the earth fault indication returns back to normal. Isolation of all machinery, which operates on 440V is not always possible. Certain critical equipment like steering gear and lubricating oil pumps cannot be isolated when the ship is underway. However changeover can be done from running machinery to the standby one and the earth fault can be found.

Finding Earth Fault on 220V Circuit

Finding an earth fault on a 220V circuit is comparatively difficult than a 440V circuit. The main reason being the lighting circuits found all round the vessel. However, any earth fault alarm with respect to a 220V circuit is usually treated as important but not an emergency.

When a 220V earth fault alarm sounds, as said earlier, pressing the test button checks the trueness of the alarm and then investigation can be started on each and every 220V circuit.