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.
 
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?
A lot of good comments, but I think your questions are partially answered. So, let me try and fill the gaps in:
All SF6 breakers have an internal safety mechanism which will lock-out a closed breaker in closed position, if the gas pressure becomes lower than a threshold value (set out by the manufacturer). This is to ensure that the breaker cannot be attempted to be open when the its interrupting capability is severely compromised. Although I do not know for certain, but I anticipate this dangerously low pressure (ie, the lock out pressure) will be lower than the SF6 low low alarm.

What will happen if there is a fault on the system and a trip is issued to the breaker which is locked-out closed? Well, the CB fail will clear the fault in CBF time via taking a larger portion of the system out.

If the leak is slow and gradual, I would follow the SF6 top up procedure as my 1st option. If top is not possible or leak is bad, then follow the de-energisation procedure.
 
In general a generator is connected to a step-up transformer via an 11.5Kv circuit breaker before being connected to the grid, and the transformer is connected to the grid via a 30Kv or 220Kv circuit breaker or other, in the event of a drop in SF6 pressure the circuit breaker 30 or 220 Kv can be used to isolate the generator. If we manage to repair the 11.5 circuit breaker so much the better, if not we transmit the opening signals of the 11.5kv circuit breaker to the 220kv circuit breaker for protection. We have operated with this configuration for more than a year by keeping the 11.5 Kv circuit breaker closed and synchronizing with 220kv circuit breaker
 
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