Preferential trip:

Preferential trip is a kind of electrical arrangement on ship 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’s which can be disconnected momentarily and can be connected again after fault finding. 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 and thus prevents blackout and overloading of generator.

Reverse power trip:

There is not much difference between an alternator and electric motors from the engineer’s perspective. They are both based on similar principles. So just imagine what would happen if an alternator
suddenly would act as a motor. This is only possible in systems where two or more generators are running in parallel. Hence this type of protection system is used only if there is more than one alternator on board
a ship. The system is designed in such a way that it will release the breaker and prevent motoring of
alternator if a reversal of power occurs. This protection device is also used to prevent damage to the prime mover, which might be stopped due to some fault. Though it is extremely difficult to detect reverse current
with an alternating current system, reverse power can be detected and protection can be provided by reverse power relay


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