Generator Circuit Breaker low SF6 pressure in close position

Can anyone explain the status of GCB (Generator Circuit Breaker) in close position getting low low SF6 alarm, what will happened, will it open on low low pressure? if not then how to shut down the prime mover (Gas Turbine). During this condition it may be chance of trip protection called, so what should do as a operator?
 
SF6 is used for arc suppression in medium and high voltage breakers. I recommend removing the gas turbine from service.
Then find leaks and recharge the breaker with SF6.

Since the gas turbine will lower load to near zero before opening the breaker, arcing is minimal.

However, if the turbine were to trip from full load a very large and destructive arc could occur.
 
Mr. Lodi...
For increased safety:
Assuming gen'r CB in question is connected to a "live" grid, then it is best to lower load-flow, with load PF as close to 1.0 as possible. Then open Gen'r stator CB at lowest current value reached before "reverse power" occurs.

For the reason why, refer to an earlier topic: "How PF Affects Breaker Performance" !

Regards Phil Corso
 
SF6 is used for arc suppression in medium and high voltage breakers. I recommend removing the gas turbine from service.
Then find leaks and recharge the breaker with SF6.

Since the gas turbine will lower load to near zero before opening the breaker, arcing is minimal.

However, if the turbine were to trip from full load a very large and destructive arc could occur.
Good to read...
It is operator action. What should be system design configuration. What will be automatic reaction on low low sf6 alarm?
 
Mr. Lodhi,

What will be automatic reaction on low low sf6 alarm?
I do not have access to your generator protection drawings or settings.
I would have removed the generator from service when the low alarm became active. I would not have waited for LOW LOW.
Mr. Lodi...
For increased safety:
Assuming gen'r CB in question is connected to a "live" grid, then it is best to lower load-flow, with load PF as close to 1.0 as possible. Then open Gen'r stator CB at lowest current value reached before "reverse power" occurs.

For the reason why, refer to an earlier topic: "How PF Affects Breaker Performance" !

Regards Phil Corso

Therefore, all I can recommend is to remove the generator from service to allow for servicing the generator breaker.

My experience with SF6 breakers is that no one ever performs service on a closed breaker. Usually the breaker is opened and isolated from the high voltage bus. Then the servicing begins.

Hope this helps.
 
Mr. Lodi...
For increased safety:
Assuming gen'r CB in question is connected to a "live" grid, then it is best to lower load-flow, with load PF as close to 1.0 as possible. Then open Gen'r stator CB at lowest current value reached before "reverse power" occurs.

For the reason why, refer to an earlier topic: "How PF Affects Breaker Performance" !

Regards Phil Corso
PhilCorso,

You bring up a very valid point.

The turbine control system in shutdown control does not try to handle PF. The AVR merely maintains the voltage that it was at when the STOP command was given.

However, an operator could perform some procedures that would allow for PF to be at unity before the the shutdown command was given.

Even further, the operator could place the turbine in preselect and lower load and then check for unity.

My point is the OP should have never let the condition get to a LOW LOW condition.
 
Mr. Lodhi,

Another important note, The gas turbine will need to be on cooldown for a day before the high voltage bus voltage can be removed from your generator step up transformer. One day of cooldown before the breaker can be serviced.
 
Got it.

Actually i see in drawing the tripping circuit will operate on low low sf6 logic which blink me to raise this question. I see it again
 
And one thing more Low alarm is normally appeared in winter season when ambient temperature goes minus, that time GT dont tripped, we just use portable heater for sometime after that low alarm clear.
 
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