A relay is an important electromechanical safety device in ship’s electrical circuit and is normally used to open the faulty circuit from the main supply when any kind of electrical fault occurs. A relay is fitted in the Main and Emergency switch board of the ship as a protective device.
Relay has to be kept operational and healthy at all times, else at the time of fault if it relay does not operate properly, the whole system may suffer loss of power or damage. The most common application of relays is for overload and short circuit protection.
A ship engineer or electrical officer has to make sure that relay is efficiently in operation and all the maintenance is carried out on the same as per schedule or as per continuous monitoring.
If during inspection, the relay is found out to be defective it must be replaced immediately with a spare one.
A simple electromagnetic Relay is shown in the below diagram and it will get activated when the magnetic effect of the iron core is sufficiently increased by the excess or high current in the coil which will attract the iron armature held against the spring force to trip the circuit.
A brief maintenance for relay is given as follows-
- Checks to be carried out on relay contacts for damage due to arcing.
- Polish the contact with emery paper to remove rust and deposits.
- Check the closing linkage for free movement.
- Check the continuity of the contacts with multimeter.
- There are arc chutes provided to quench the arcing. Check for burnout of the same.
- Check the tension of the spring.
- Open circuit and short circuit test to be performed on the coil by multimeter.
- Check the continuity of the trip circuit by multimeter.
- Check tightness of the supply terminals.
You may also like to read-Permanent magnet moving coil instrument (PMMC)
Reference and Image Credits:
Book on Marine Electrical by H.D. Mc George