Earth fault is considered very critical on board a ship. Some ships which operate at 440 V 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 which isolates when a machinery suffers an earth fault. How to find out 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. Any 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 to 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 of isolating each and every machinery in the 440 V circuit and check whether 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 for when the ship is underway. However changeover can be done from running machinery to the standby one and thus the earth fault can be found.
Finding Earth Fault on 220V Circuit
Finding an Earth Fault on a 220V circuit is...