Gas Characteristics Before The Energization; Procedure For Bushing Gas Compartment Decontamination; Procedure For Bushings Equipped With The Gas Filling Station - GE PHI 530.1425.2500 Operating And Maintenance Instructions Manual

WARNING: The gas re-filling operation MUST be performed with the bushing de-energized and
grounded. Safety prescriptions of Chapter 2 must be followed.
WARNING: The refilling action must be performed by qualified operators. The risk is that a wrong operation can
drain the gas from the bushing with possibility of plant tripping and equipment damages if the gas leakage will
be excessive.
WARNING: Always use equipment certified for SF6 gas. This will avoid mistakes, safety issues and risk for the
environment and the equipment.

8.3 Gas characteristics before the energization

Before the energization the gas parameters must be checked and, in particular:
Gas data must be recorded on a check list.
9

Procedure for bushing gas compartment decontamination

This part is applicable only in case of evidence of internal contamination by moisture.
It is applicable to the following cases:
SF6 transport pressure below the specified limits and / or with gas dew point ≥-30° C at atmospheric
•
pressure.
Evidence of gas dew point ≥ -20° C at rated filling pressure before the energization.
•
Evidence of gas dew point ≥ -18° C at rated filling pressure during the normal operation.
•
Opening of the bushing for internal inspection.
•
Note: This procedure in not applicable in case of evidence of internal pollution by dust and other solid particles.
This operation can be performed also with the bushing installed on the transformer.
The procedure requires the use of dry Nitrogen with a dew point < -55° C.
The operation is slightly different if the bushing is provided or not with the gas filling station.
9.1

Procedure for bushings equipped with the gas filling station

Connect a digital pressure gauge to the DILO valve at the level of the bushing flange.
•
Connect the DILO machine to the gas filling station DILO valve.
•
Start the DILO machine, recover all the gas of the bushing and store it in clean gas bottles.
•
Put the bushing under vacuum until the residual pressure measured at the bushing level will be <10 Pa
•
abs (0.1 mbar abs).
Keep the vacuum for at least 12 hours.
•
Stop the pump and connect the Nitrogen bottle at the DILO valve placed on the gas filling station. The
•
gas dew point must be < -55° C.
Fill the bushing with dry Nitrogen at 0.25 MPa abs (1.5 bar gauge).
•
HVDC TRANSFORMER BUSHINGS
Parameter
Gas Purity
Gas Dew point @ rated filling
pressure
SO2
Other pollutant
Table 15 – Gas parameters limits at the bushing energization
PHI 530.1425.2500
PHI 265.850.1500
Kepco project
Value
> 99.6 %
< -20° C
Absent
As in Table 14
IS 2664 GB
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