145 kV HV GIS Switchgear - electrical strength under SF6 leakage?

[milosz125]

Hello

Considering HV switchgear rated for 145 kV 3 phase 50 Hz. All 3 phase busbars are in one enclosure so 3 phase or 2 phase faults are possible.
Assuming system failure (leakage) and SF6 pressure drop below 2 stage alarm level in feeder
compartment, does the electrical strength of the system still maintained?

I mean that typical distance for HV 3 phase air insulated busbars rated for 145 kV is around 1.1m (3.6 ft.).
In GIS switchgear for space saving issues busbars are closer each other, but in SF6 gas environment which has stronger electrical strength.
In normal condition pressure of SF6 gas in feeder compartment is around 0,6 MPa (87 PSI), but when pressure of SF6 drops severely
how to maintain electrical strength of the compartment. Compartment has own SF6 pressure loss detector which alarms remote control center, but HV voltage
at cable feeder is still present. Is sparkover between busbars serious threat in such conditions?

Greets

 

[rcwilson]

You need to get the specific information from the manufacturer.

Usually, GSIS switchgear is designed to withstand normal voltage at 1 atmosphere of pressure. At that pressure, the SF6 gas and the outside air are at the same pressure and gas cannot leak very much, unless the bus enclsoure has ruptured or has been broken.

If there is a rupture or a fast leak, you need to trip the bus. If the gas has leaked out to an alarm condition, you need to make plans to take a maintenance outage before a switching surge or other voltage spike causes a flashover.

Gas leaks are rare and are usually slow, so this philosophy is practical. A fast or sudden gas leak is probably from external damage so the bus should be tripped.

 

[milosz125]

Thank you for that explanation.

You need to get the specific information from the manufacturer.

Usually, GSIS switchgear is designed to withstand normal voltage at 1 atmosphere of pressure. At that pressure, the SF6 gas and the outside air are at the same pressure and gas cannot leak very much, unless the bus enclsoure has ruptured or has been broken.

If there is a rupture or a fast leak, you need to trip the bus. If the gas has leaked out to an alarm condition, you need to make plans to take a maintenance outage before a switching surge or other voltage spike causes a flashover.

Gas leaks are rare and are usually slow, so this philosophy is practical. A fast or sudden gas leak is probably from external damage so the bus should be tripped.

 

[meternerd]

It was my understanding that the SF6 is there to interrupt the arc during a trip. I thought the bushings and separation provided the insulation. In our stations in Alaska and here in the Sierras, we have cutout features to disable tripping on low pressure. This usually happened when the heaters failed and the temperature was below -30 deg F. SF6 will liquify at those temps, and the insulation value drops. The 345 lines remained energized during the few times it happened.