Saturday, 10 September 2016

Anti Pumping Relay in Circuit Breaker

Anti Pumping Relay is used in a Circuit Breaker to indicate the spring failure of TNC i.e. Trip Neutral and Close (TNC) switch. TNC switch is used to manually Open and Close the Circuit Breaker either from Local or Remote.

This is called TNC switch as it has three positions namely TRIP, NEUTRAL and CLOSE. This type of switch is spring loaded switch i.e. to close the Circuit Breaker one need to move the TNC switch from NEUTRAL position to CLOSE position and then due to spring the switch automatically will come to NEUTRAL position. Thus even though the Circuit Breaker is Close, the position of TNC switch will be at NEUTRAL. Same is the case for tripping the Circuit Breaker.

The function of Anti Pumping relay is to cut off the supply to CB closing coil in case of TNC switch spring failure and prevent CB hunting effect i.e. continuous closing, opening operation.

Anti pumping is also called Trip Free Mechanism of any Circuit Breaker. Why it is called Trip Free Mechanism?

Suppose the Circuit Breaker has been closed by manually by pressing the TNC switch. The operating mechanism will start operating for closing operation.

Meanwhile a fault has taken place and fault sensing relay gives a trip command to the Circuit Breaker. The Trip Free Mechanism / Anti pumping feature ensures that the Circuit Breaker is tripped by protective relay even if it is under process of closing.

What will Happen if Anti Pumping Relay is not Present?

Suppose the Circuit Breaker is closed using TNC switch, and at the same instant spring of TNC switch fails and it did not came to its NEUTRAL position. So continuos supply will be available to the Breaker closing coil.

Assume a fault occurred and the protection relay had been operated at this instant and opened the CB. Since supply is continuously available to the Circuit Breaker closing coil because of TNC spring failure, then CB will close again, since fault is still persisting the Circuit Breaker will trip. In this way the continuous Circuit Breaker opening and closing will take place which may damage Circuit Breaker operating mechanism.

This phenomenon of continuous Circuit Breaker opening and closing is termed as Circuit Breaker hunting.  That is why to prevent Circuit Breaker hunting, Anti Pumping Relay is used.

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