Oil Pressure Vs Average Temperature; Oil Pressure Gauge - GE PHI 530.1425.2500 Operating And Maintenance Instructions Manual

6.1 Oil pressure vs average temperature

PHI bushings are sealed and pressurized devices. To compensate the oil volume variation by the temperature,
each unit is provided with a built-in expansion vessel system equipped with internal bellows (Prysmian expansion
vessel).
This expansion system allows to maintain a positive pressure at the minimum expected oil temperature,
generally equal to the minimum specified ambient temperature, and the maximum oil expansion volume related
to the oil maximum average temperature during the bushing operation.
On the basis of the above-mentioned design concepts and the specific technical characteristic of the selected
expansion vessels, the next Figure 8 shows the curves Pressure vs Average oil temperature for the two PHI
bushings.
This curve is used in GE Factory to set the proper oil pressure at the end of the bushing production process and
it is also useful to check the bushing status during the operation by controlling the oil pressure on the built-in oil
pressure gauge, see next Paragraph 6.2.

6.2 Oil pressure gauge

To monitor the pressure important parameter each unit is provided by one or more pressure gauges, provided
with electrical contacts (see Figure 9).
The events that can be detected by this pressure gauge are:
Low oil pressure, related to the possibility of an oil leakage from the oil impregnated paper section.
•
High oil pressure, related to an internal fault in the oil impregnated paper section or a gas leakage from
•
the gas section of the bushing.
HVDC TRANSFORMER BUSHINGS
Figure 8 – Oil pressure vs. average oil temperature
PHI 530.1425.2500
PHI 265.850.1500
Kepco project
IS 2664 GB
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