Closing Circuit of 33 kv Outdoor Gang Operated Vaccume Circuit Breaker

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There are following elements in the Closing Circuit:

1. Closing Coil
2. TNC Switch
3. Closing Resistance
4. NC Aux Contact 52b
5. Antipumping Relay
6. Local Remote Switch

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Closing Coil:

1. A permanat Negative (K2) is given to one end of the Closing Coil.
2. When Positive is extended to Closing Coil, through the TNC Switch, the Closing Coil Energises and attracts the Closing Plunger, which inturn activates, the Closing Mechanism and the Breaker Closes.
3. Please note that the Closing Coil is not designed for Continous supply, because they don’t need to.  And so when a Continous Dc is applied to it, it gets burned.

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TNC Switch:

1. Positive is given to one end of the TNC Switch
2. When turned to C, it extends the Pulse to the Closing Coil and then with the help of Springs, returns back to Neutral (N) Position. Thus, it is used to give a pulse.

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Closing Resistance:

1. A Resistance is used just before the Closing Coil to limit the flow of current through the Closing Coil.

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Normally Close (NC) Auxillary Contact- 52b:

1. Closing Coil are not designed for Continous Supply. 
2. When the TNC Switch is put on “C”, it gives a pulse to the Closing Coil and then return back to the Neutral (N) Position.
3. Now, if  the TNC Switch Spring fails, it may get stuck up at “C”, which results in Continous Supply being getting extended to the Closing Coil, burning the Closing Coil.
4. Hence, we use a Breaker NC Auxillary Contact called as 52b, in the Closing Circuit. As, soon as the Breaker turns ON, the 52b opens up, breaking the Closing Circuit and therby protects the Closing Coil from Continous Supply. For Details on the Auxillary Contact and Auxillary Switch, click on the Link : Auxillary Contact.

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NC Antipumping Contact:

1. When we give the Closing Pulse and the TNC Switch gets stuck up at C, the Auxillary contact 52b opens up and breaks the Closing Circuit.
2. But, 52b may be sluggish in operation, exposing the Closing Coil to Voltage for higher periods and may result in burning of the Closing Coil. Therefore, we need a faster operating Contact and hence the need for the Antipumping Device.
3. We connect the Coill of the AP Relay across the Closing Coil and its NC Contact in series with the Closing Coil.
4. Once the Closing Command is given through the TNC Switch, the Closing Coil gets operated and at the same time,  AP Relay gets energised, and its NC Contact opens, breaking the Closing Circuit faster than the NC Auxillary contact 52 b , therby protecting the Coil. Also, it prevents the Hunting Effect in the Circuit Breaker.To know more about the Antipumping Relay , click on the Link : Antipumping Relay in Circuit Breaker.

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The Breaker can be Closed Locally in the Yard using the TNC Switch of teh Breaker or Remotely through the Control Room Using the TNC Switch in the Relay Panel/Control Panel.

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Local Closing:

1. Positive is given to the Local/Remote (LR) Switch in the Breaker. When the LR Switch is in the Local Mode, Positive gets extenede to the TNC Switch. When the TNC Switch is kept on C, the Positive is extended to the Closing Coil and thus the Breaker Closes Locally.

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Remote Closing:

1. When the Breaker is OFF and under Maintaince, we switch the DC MCB, so that the Breaker cannot be closed, so as to avoid any accident, in case someone Closes the Breaker.

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