Question 1

What is the need of an LR Switch in an HV/EHV Circuit Breaker?

Accepted Answer

The LR Switch, when kept on the Local Mode (during Breaker Maintenance), will not allow the Closing of the Breaker Remotely, thereby ensuring the Safety of the personnel working on the Breaker.

So, when someone needs to work on the Breaker (Under Shutdown) , he can and should put the LR Switch in the Breaker in the Local Mode, so that the Breaker cannot be closed Remotely i.e. from the TNC Switch in the Control Room, ensuring his Safety.

Question 2

How is the Wiring carried out of the LR Switch in the Breaker? And what is Closing Positive K5 ?

Accepted Answer

The LR Switch Contacts are wired in Closing Circuit, in such a way that, instead of giving the DC Positive directly to Local TNC (Breaker TNC) and Remote TNC (CP/RP TNC) , it is given through the Local-Remote (LR) Switch in the Breaker.

In the Breaker Closing Circuit, the DC Positive (K1) is first given to the LR Switch in the Breaker and from there, it can be extended to Local TNC Switch or Remote TNC Switch

If the Breaker is the Local Mode, the DC Positive is extended till the Local TNC (Breaker TNC Switch) and not to the Remote TNC Switch and so the Breaker can be closed Locally, but cannot be closed Remotely.

When the LR Switch is kept in the Remote Mode, the DC Positive is extended to the Remote TNC Switch, this DC Positive is called Closing Positive K5.
It is so called because, this DC Positive is specifically used for Breaker Closing, when the Remote TNC Switch is kept on 'C' (K5 becomes K21).

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