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Minimum impregnation time under vacuum: ≥ 12 h.
o
Recirculation of the internal side of the pressboard barriers from the DN25 internal pipe
•
Oil treatment plant connected to point 'A' to bottom valve 'B'.
o
Recirculation steps: 'A' 'B', 'B' 'A', 'A' 'B' (Top to Bottom, Bottom to Top, Top to Bottom).
o
Min. number of oil passes of total oil volume for each recirculation step: 3.
o
Temperature of the oil at the return pipe:
o
Recirculate the internal part of the barriers until parameters are in line with Table 13 data.
o
Recirculation of the outer side of the pressboard barriers
•
Oil treatment plant connected to valve 'B' and 'C'.
o
Recirculation steps: 'B' 'C', 'C' 'B' (Bottom to Top, Top to Bottom).
o
Min. number of oil passes of total oil volume for each recirculation step: 1.5.
o
Temperature of the oil at the return pipe:
o
Recirculate the outer side of the barriers until parameters are in line with Table 13 data.
o
Bushing installation
•
Break the vacuum in the turret via a silica gel breather.
o
Drain from valve 'B' an oil volume corresponding to the bushing oil side volume (approximately
o
100 litres for PHI 265 and 420 litres PHI 530 kV).
Connect the valve 'C' to a dry air equipment and circulate the air inside the turret.
o
Open the turret manhole by taking care to avoid any foreign material from dropping inside the
o
turret.
Install the bushing in accordance to the procedure at Paragraph 5.5.
o
Final filling and oil recirculation
•
Connect the oil treatment machine to the valves 'B' and 'C'.
o
Apply vacuum to the turret via the Buchholtz relay pipe.
o
Vacuum level in the turret ≤ 0.1 kPa (1 mbar).
o
Vacuum time @ vacuum level: ≥ 3 h.
o
Fill the turret from valve 'B' with treated oil as in Table 12. No air has to remain trapped inside
o
the transformer turret.
Recirculate from valve 'C' to valve 'B' (Top to Bottom) for a minimum of 2 passes of total oil
o
volume, until the oil temperature on the return pipe is ≥ 70° C and the parameters are in line with
Table 13 data.
Complete the filling operation of the transformer and apply the standing time defined for the
o
transformer procedure.
Check the oil characteristics inside the transformer turret that must be in line with Table 13 data
o
(see also Table 9 for the ISO 11218 solid contamination limits classes).
Parameter
Water content by Karl Fisher at 20° C
Breakdown voltage on 2.5 mm gap
Total gas content
Power factor at 90° C
Resistivity at 30° C
Particle content
Table 13 – Oil parameters for turret final oil filling and recirculation
NOTE:
Fibre count readings may be adversely affected by many issues; thus, the following aspects need to be ensured:
The vacuum pump is operating effectively.
•
The vacuum and pressure values are balanced in the system.
•
There are no extreme temperature influences.
•
The velocity of pumping does not cause turbulent flow or bubble evolution.
•
The sampling point is not in a position subjected to vacuum or turbulent flow which may damage the on-
•
line equipment and is reasonably close to the output of the tank circulation system.
Bottle sampling is NOT recommended as the reading may well be higher and the Class 00 criteria
•
difficult to achieve.
HVDC TRANSFORMER BUSHINGS
PHI 530.1425.2500
PHI 265.850.1500
Kepco project
≥70° C.
≥70° C.
IS 2664 GB
Page 23 of 70
Limit
≤ 2 ppm
≥ 80 kV
< 5000 ppm (0.5%)
≤ 0.005
12
≥15 10
Ohm x m
ISO11218 Class 00
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