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 equipments 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.
Construction and Working
The preferential trip circuit consists of an electromagnetic coil and a dashpot arrangement to provide some delay to disconnect the non-essential circuits. Along with this, there is also an alarm system provided, which functions as soon as an overload is detected and trips start operating. There are some mechanical linkages also in the circuit which instantaneously operates the circuit and completes the circuit for preferential trips.
The dashpot arrangement consists of a small piston with a small orifice and which is placed inside a small cylinder assembly. This piston moves up against the fluid silicon and the time delay is governed by the orifice in the piston.
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 circuit.
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 circuit diagrams which help in removing the excessive load from the main bus bar, thus preventing situation like blackout which is a dangerous incident to ship, especially when the ship is sailing in restricted or congested waters.
You may also like to read Starting of Emergency generator.
Image Credit
Marine Electrical Equipment and Practice by H.D McGeorge
i want to free download some engineering book.please allow me for that.thanking you.
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hi sir
plz tel me how an e.t.o (electro technical officer ) career now a days .Because i heard that lots of people talking abt this rank is waste, no future and recently imo ban this rank in all ships .
waiting for your reply
@ Chandrashekar:
This is an important rank in the ship. You will be joining as an Asst. Electrical officer and then you will be promoted to Electrical officer after giving exam as per STCW 2010 (Highest rank for electrical officer).
NO. This rank was never banned by IMO
Can you give me detailed instruction on how to simulate or test preference trip onboard ship. I’m an electrical officer. thanks
Operating character appear on the nameplate in an A/C motor
a. Temp. Rise
b. Input kW
c. Rotor torque
d. Type of wibding
sir gooday may I ask how to trouble preference trip,, im an on board electrian
how to test the preferential trip and overload trip while generator running in parrellel
emergency generator not coming into service during blockout situation what was problem over there.
Good morning to eto frnd
Im getting trouble in preference tripped in ums ship
When im tried to generator safety alarm is working good
Problem is when i tried to generator shutdown tripped mean lube oil low pressure shutdown tripped then preference tripped happened without load at acb open condition
What could be reason plz advise me
Why nowadays we have only 2 preferential trips 5 and 10 seconds ?
Why 15 seconds is trip is eliminated?
@Monzur: because of the local level trips and added safety/ Automation.