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Trip circuit what its functions

A trip circuit should be always ready to trip or disconnect an electrical system ormechanical system. Trip circuit receives signal from the protection system watch doglike relays, PLC etc. After receiving a signal trip circuit initiates the opening ordisconnecting means of a circuit by opening or disconnecting a circuit breaker by meansof actuating some mechanical or electrical systems. This electrical or mechanicalsystems might be spring, motor. As to open a circuit breaker it will require somestrength. o a relay as a watch dog is always activated also the trip circuit but on theother hand the circuit breaker is always inactive.

Why the trip circuit is required to be live always:

As the trip circuit has some important purpose the functionality or health of it must beensured. !hat happens if a trip circuit is open or damaged" #n this case the circuit willbe totally unprotected. The relay$ PLC will send out signal after happening a fault but astrip circuit is dead , the breaker will not open or disconnect.

In a protection system the tripping of a circuit breaker is crucial. If an interruptionoccurs in the trip circuit, the possible network fault will not be disconnected and thefault would have to be cleared by another protection upstream in the power system.The supervision function is particularly important when there is only one tripping coil

and CB tripping is vital. (For instance, in the case of generator circuit breakers or anyother important circuit breaker in distribution networks.

Functions of a typical trip circuit supervision relay

%alvaa&Below is trip circuit supervision relay function described based on a specificmodel! the settings and data might varied to models but the core principle is same.

The supervision function is based on a low'level () * mA+ current inection principle.

The inected current is sensed by two opto'couplers. The supervision function in threesteady states of circuit breaker'trip circuit is below image.#n normal condition theindicator L- glows green and output relays are in /picked'up0 condition. #n the event ofa fault, the measuring current goes below the operating value of the relay (1.* 2 1.3 mA+or completely stops flowing.

The supervision relay operates (drops'off+ after a delay of 1.4 sec and the indicator L-turns red. The supervision relay, for its functioning requires an au5iliary voltage (AC or

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C+ of a rated value . This voltage can be the same as that of the supervised circuit or itcould be a separate source with same magnitude (AC or C+. hould a fault occur in theau5iliary voltage supply, the L- does not glow and the output relay drops off. 6elayswith differing rated voltage for supervision circuit and au5iliary supply can be suppliedas a special e5ecution.

Tri

p circuit supervision relay function

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