Operate the SF6 GIS (Gas Insulated System) only within the range of its rated gas pressure. If The GIS's gas pressure drops below its rated level, check for depleted gas supplies and/or system leak.
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To prevent equipmnet malfunction, check the GIS gas system schematic diagram to confirm safe gas pressure levels and system operation status before opening/closing any system valves.
For CB (Circuit Breaker), rated gas pressure is 7 Bar and admissible minimum gas pressure is 6.5 Bar.
For DS (Disconneting Switch) or ES (Earthing Switch), rated gas pressure is 6.5 Bar and admissible minimum gas pressure is 6.0 Bar.
And for the Bus Bar or other compartement, rated gas pressure is 6.0 Bar and admissible minimum gas pressure is 5.5 Bar.
Before starting any work on OHL 500kV, disconnect the breaker from network and earth, switch off control current and vent SF6 gas, pressurized air.
SF6 gas losses due to leaks
Leakage kan occur at SF6 gas lines, pipe connection, rubber seals, welded joint.
Detect the leakage point by detector.
Tighten screwed connection, if leak persists, replace faulty components.
Replace the damaged or faulty seals.
Solder at site.
Evacuation and filling of SF6 gas.
Evacuation and filling of SF6 gas can be executed by the following two apparatus.
Gas transfer equipment constructed from vacuum pump gas compressor, storage tank and control device.
Gas supply equipmnet constructed from SF6 gas cylinder and control valve and vacuum pump.
Evacuation.
Confirm the valve of each pole attached to the gas tank body is open.
Exhaust SF6 gas to atmosphere from vent valve.
Filling.
Detach the blind cover from the valve.
Connect flexible hose with the valve installed on the gas tank body of each pole.
Open the valve.
Continue to operating of vacuum pump more than one hour after attainment of 1.0 mmHg vacuum degree.
Shutdown the vacuum pump.
Confirm that the valve on the gas tank is to be closed.
Connect gas cylinder and pressure reducing valve to the valve temporary with flexible hose, and the loose connection should be applied between the flanges of the valve and the hose.
Open cylinder valve slightly and blow SF6 several ten secands to evacuate the air inside the hose and close the cylinder valve.
Fasten the flanges between the valve and the hose immediately.
Open cylinder valve and fill SF6 gas with watching the gas pressure gauge.
Fill SF6 gas a little bit higher than the rated gas pressure (7.2 ~ 7.5Bar at 20C) and should be measure the gas pressure afetr SF6 gas temperature is stabilized.
Close the valve, disconnect the hose and attach blind cover to the valve.
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