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5 Commissioning
5.1 Waiting time before energization
Waiting times after oil-filling of the transformer
Some waiting time is necessary after the transformer has been oil-filled, before the bushing is energized. The
reason for this is that air bubbles stick to the bushings surface when the transformer is filled with oil, and
flashovers and partial discharges can form in the bubbles. Thus, it is important to let the necessary waiting
time pass, to make sure that all the air bubbles have risen to the surface of the oil before the bushing is
energized. Refer to the table.
The transformer is oil-filled with
The vacuum process
Gas-saturated transformer oil
De-gassed transformer oil
A reduced oil-level
5.2 Recommended tests before energization
5.2.1 Overview
The tests should be done to check the insulation, sealing and current path of the bushing.
NOTE!
The tests should be done after installation, but before connecting the outer terminal of the bushing
to the power circuit.
5.2.2 Tightness test between transformer and bushing flange
Many different methods can be used, and we thus refer to the instructions given by the company responsible
for field erection.
For example, the tightness of the seal between the transformer and the bushing flange can be examined when
the transformer is oil-filled, with chalk or paper strips.
Installation and maintenance guide
1ZSC000563-AAB EN, REV. 6, 2019-09-12
Necessary waiting time
No waiting time is necessary, air bubbles does not
form in vacuum. Refer to the transformer
manuafacturers instructions.
After the oil-filling process has been completed, wait
for 24 hours before energizing the transformer.
After the oil-filling process has been completed, wait
for 6 hours before energizing the transformer.
After the oil-level has been restored, wait 24 hours
before energizing the transformer.
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