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8.1 Gas first filling operation and control of alarm and tripping signals
The bushing is shipped in slight overpressure of SF6 gas. If the pressure is positive proceed with the operation
as follows, on the contrary, contact GE Energy Connections Supervisor for additional instructions.
Check that the Transport pressure gauge has been removed (see Figure 1).
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Check the gas characteristics and fill the data on the Gas filling check list, see Appendix 8.
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Connect the gas plant to the DILO filling valve 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
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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
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leakages stop the activities and contact GE Energy Connections Supervisor.
If the bushing does not show any leakage gradually increase the pressure at the rated filling pressure
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value of 0.63 MPa (5.3 bar gauge). The pressure must be directly measured on the compensated gas
density monitors installed on the bushing flange.
During the pressure rise, check the functionality of the Tripping (0.52 MPa abs), Alarm 2 (0.55 MPa abs)
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and Alarm 1 (0.58 MPa abs) contacts and record the respective operating pressures on the bushing
check list, see Appendix 7. In case of malfunction, check the wiring and inform GE Energy Connections
Supervisor.
During the alarm / tripping functionality test, record on the bushing check list the readings on the two
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gas density monitors.
Keep the bushing at the rated filling pressure for 4 hours, the purpose of this standing time is to allow
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the gas temperature stabilization, then make the final adjustment of the gas pressure.
Disconnect the gas plant from the DILO filling valve located on the bushing flange.
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The gas density monitors installed on gas bushings are 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 a gas average temperature of 20° C. This condition is directly related to the
gas density inside the bushing (see Chapter 10).
8.2 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 refilling operation has to be done within 7 – 10 days after Alarm 1 intervention and it is mandatory to perform
it within 1 – 2 days after the Alarm 2 intervention.
Gas refilling can be done from the 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:
Check the gas characteristics and fill the data on the Gas filling check list, see Appendix 8.
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Connect the gas filling equipment (gas plant or SF6 system for direct filling from gas bottles) to the filling
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valve of the bushing flange.
Gradually and slowly increase the gas pressure up to the rated filling pressure value of 0.63 MPa abs
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@20° C (5.3 bar gauge). Pressure must be directly measured on the temperature compensated pressure
gauge installed on the bushing.
Stop the gas filling equipment and shut the bottle valves.
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Disconnect the filling equipment from the gas filling station DILO valve.
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NOTE: In case of use of the DILO machine, check that the machine set-up is for gas filling and that the
connecting pipe is full of SF6 before connecting to the gas filling station DILO valve.
In case of direct filling from the bottle, check that the bottle is effectively charged with SF6, that the gas quantity
is sufficient for the re-filling, the pressure reduction unit and the pipe are compatible with the DILO filling system
and all equipment is specific for SF6 filling application and certified for a safe use. Also in this case, before
connecting the equipment to the gas filling station, check that the connecting pipe is effectively filled by SF6 gas.
HVDC TRANSFORMER BUSHINGS
PHI 530.1425.2500
PHI 265.850.1500
Kepco project
IS 2664 GB
Page 25 of 70
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