Nuova Via di Piano Comprensorio Vulcano
Sesto San Giovanni, MI 20099 Italy
Tel. 02-24105.001
IS 2653 GB
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6.1
Gas first filling operation and control of alarm and tripping signals
The bushing is shipped in slight overpressure of SF6 gas (See Chapter 5.1). If the pressure is positive proceed
in the operation as follows, unless contact GE Grid Solutions RPV Supervisor for additional instructions.
•
Install a calibrated vacuum / pressure digital gauge to one DILO valve on the bushing
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Connect the vacuum pump to another DILO valve on the bushing
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Start the vacuum pump and reach 1mbar residual pressure and keep it for 12 hours
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Stop the vacuum and connect a dry nitrogen bottles pack to another DILO valve on the bushing
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Fill the bushing at 1,5bar abs (0,5 bar gauge) and maintain the pressure for 12 hours
•
Check and record the dew point of the gas and the pressure
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Remove the gas by restarting the vacuum pump and set a vacuum level of 1 mbar residual
pressure and keep it for 6 hours
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Stop vacuum and fill with dry nitrogen at 1,5 bar abs (0,5 bar gauge) and maintain the
pressure for 12 hours
•
Check and record the dew point of the gas and the pressure. The dew point of the gas should be <= -
48°C at atmospheric pressure (-44.6°C at 1,5bar abs)
•
Start the vacuum pump and reach 1 mbar residual pressure and keep it for 24 hours
•
Fill the bushing with SF6 at 1,2 bar abs and wait 24h. SF6 should be of the quality provided in the
instruction manual and checked before filling.
•
Check the gas parameters the moisture content must be <= 15 ppm weight (122 ppm vol). If gas
parameters are OK, proceed with the installation of the bushing, unless contact RPV for additional
instructions.
•
Carefully reinstall the density meters to avoid any damage on the gaskets.
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Connect the gas plant to the gas filling DILO type valve located on the bushing flange.
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Gradually increase the gas pressure up to 0.2 MPa abs (1 bar gauge). Pressure must be directly
measured on the gas density monitors installed on the bushing flange.
•
Check all the gas seals for leakages with a suitable SF6 leak-meter device. In case of significant
leakages stop activities and contact GE Grid Solutions RPV supervisor.
•
If the bushing does not show any leakage, gradually increase the pressure at the rated filling pressure
value, the pressure must be directly measured on the compensated gas density monitors installed on
the bushing flange.
•
During the pressure rising, check the functionality of the alarms signal contacts and record the
respective operating pressures on the bushing check list. In case of malfunction, check the wiring and
inform GE Grid Solutions Supervisor.
•
Keep the bushing at the rated filling pressure for 4 hours, the purpose of this standing time is to allow
the gas temperature stabilization, then make the final adjustment of the gas pressure.
•
Disconnect the gas plant from the gas filling valve and close it with its cap.
The gas density monitor installed on the wall bushing is fully thermally compensated devices that indicate the
pressure independently from the effective gas temperature. Whatever the temperature of the gas, the
instrument indicates a pressure equivalent to an average gas temperature of 20°C. This condition is related
with the gas density inside the bushing.
6.2
Gas refilling during the bushing normal operation
The bushing is a fully sealed unit and its leakage rate is <0.5% x year. Anyway, after many years of operation it
could be necessary to refill it. The bushing refilling can be done with the bushing out of operation. The refilling
operation has to be done within 7 – 10 days after Alarm 1 intervention.
Gas refilling can be done from the DN 20 DILO type valve located on the bushing flange by a gas plant or a
SF6 bottle, equipped with the appropriate pressure reduction equipment and DILO connecting plug (contact
DILO GmbH for information about filling set equipment for direct bottle filling).
The filling procedure is here below described:
