What are the steps to carry out restoration, when LBB Operates at a Substation ?

Bynitinnarvekar9

First, we will try to understand what LBB is and why it operates.

What is LBB? and When does it Operate? 

Ans: LBB is a Backup Protection to the Breaker, which operates in case the concerned Circuit Breaker fails to operate in 200 ms, by tripping all the Fault infeeds ( all the Circuit Breakers in that section and the Bus Section Circuit Breaker, if it exists).
It uses the Busbar Protection for the same.

Now, the main question, 

What are the steps to carry out restoration, when LBB Operates at a Substation ?

Ans: Lets say LBB Operates at a Substation, here are steps one can take for restoration:

  1. Identify the Section whose LBB Operated.
  2. In that Section, identify the Breaker whose one or all the three Poles are closed or stuck up.
  3. Since that section is dead, the Isolator of the Faulty Breaker can be opened.
  4. Once the Isolator of the Faulty Section is opened, the rest of the Bus Section can be taken in Service.
  5. Now the Faulty Breaker can be attended.

If there is a Transfer Bus, we can take the Feeder/Transformer in Service through Transfer Bus.

But, if there is no Transfer Bus, we need to attend to the Breaker not tripping problem immediately.
Now, the Breaker not tripping on Fault, problem may be either Mechanical or Electrical.

We need to take Mechanical Trials of the Breaker to check if it’s a Mechanical problem.

If the Breaker Mechanical operations are ok, then we need to check the Electrical Operation.

For this we need to close the Breaker and give the Trip Trial through the Relay. 

The Master Trip Relay (86) should operate. If it does not operate, we need to find the problem.

If the Master Trip Relay Operates correctly, then the Breaker should Trip. If the Master Trip Relay Operates and still the Breaker does not Trip, it means there is some problem in the Tripping Circuit.

Thank you.

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