Electric Generator Safety On Ships

Generators onboard ships are the power suppliers for the entire vessel and are the primary sources of power to all running machinery systems, including the propulsion plant. For this reason, safe and efficient running of the ship’s generator has to be given highest consideration. Two important safety measures of generators are: Preferential trips and Air Circuit Breaker (ACB). Preferential trip is a kind of electrical arrangement, which is designed to disconnect the non-essential circuit i.e. non-essential load from the main bus bar in case of partial failure or overload of the main supply.

The non-essential circuits or loads on ships are air conditioning, exhaust and ventilation fans, and galley equipment, which can be disconnected momentarily and can be connected again after faultfinding. The main advantage of preferential trip is that it helps in preventing the operation of main circuit breaker trip and loss of power on essential services, thus blocking blackout and overloading of generators.

piston, with a small orifice, placed inside a small cylinder assembly. This piston moves up against the fluid silicon and the orifice in the piston governs the time delay.

Working of Preferential Trip

The current passes through the electromagnetic coil and the linkages are kept from contacting using a spring arrangement. As soon as the current value increases the limit, the electromagnetic coil pulls the linkage up against the spring force and operates the instantaneous circuit and the alarm system. The lower linkage completes the circuit for the preferential trip. The current passes through the coil in the preferential trip circuit, which pulls the piston in the dashpot arrangement.

The movement of this piston is governed by the diameter of the orifice and the time delay made by the same. The preferential trip operates at 5, 10 and 15 seconds and the load is removed accordingly. If the overload still persists, then an audible and visual alarm is sounded.

The preferential trip is one of those important electrical circuits, which help in removing the excessive load from the main bus bar, thus preventing situation like blackout especially when the ship is sailing in restricted or congested waters.