HVDC TRANSFORMER BUSHINGS
PHI 530.1425.2500
PHI 265.850.1500
Kepco project
IS 2664 GB
Page
23
of
70
o
Minimum impregnation time under vacuum:
≥
12 h.
•
Recirculation of the internal side of the pressboard barriers from the DN25 internal pipe
o
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:
≥
70°C.
o
Recirculate the internal part of the barriers until parameters are in line with
Table 13
data.
•
Recirculation of the outer side of the pressboard barriers
o
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:
≥
70°C.
o
Recirculate the outer side of the barriers until parameters are in line with
Table 13
data.
•
Bushing installation
o
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
100 litres for PHI 265 and 420 litres PHI 530 kV).
o
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
turret.
o
Install the bushing in accordance to the procedure at
Paragraph 5.5.
•
Final filling and oil recirculation
o
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
the transformer turret.
o
Recirculate from valve ‘C’ to valve ‘B’ (Top to Bottom) for a minimum of 2 passes of total oil
volume, until the oil temperature on the return pipe is
≥
70°C and the parameters are in line with
Table 13
data.
o
Complete the filling operation of the transformer and apply the standing time defined for the
transformer procedure.
o
Check the oil characteristics inside the transformer turret that must be in line with
Table 13
data
(see also
Table 9
for the ISO 11218 solid contamination limits classes).
Parameter
Limit
Water content by Karl Fisher at 20°C
≤
2 ppm
Breakdown voltage on 2.5 mm gap
≥
80 kV
Total gas content
< 5000 ppm (0.5%)
Power factor at 90°C
≤
0.005
Resistivity at 30°C
≥
15 10
12
Ohm x m
Particle content
ISO11218 Class 00
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.