Installation and commissioning guide
2750 515-1 EN, REV. 14, 2020-06-26
61
5 Commissioning
5.1 Waiting time before energization
General requirements for the bushing
•
If the bushing has been stored in the vertical position with the top end upwards, then no waiting time
is required.
•
If the bushing has been stored in an inclined position of 7°, required waiting time in the vertical position
is 24 hours.
•
If the bushing has been stored in the horizontal position then air bubbles must be removed from
condenser core surface before it can be energized. Refer to the table.
•
The waiting times can be met with the bushing installed on the transformer.
When the bushing is in the vertical position, air bubbles that are trapped in the oil collects at the top.
Storage time in the horizontal
position
Minimum required waiting time in the vertical position
Before service voltage
application
Before test voltage application
Less than one year
24 hours
24 hours
More than one year
7 days
7 days
CAUTION!
If you do not obey this procedure, flashovers or partial discharges can occur inside the bushing.
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
Necessary waiting time
The vacuum process
No waiting time is necessary, air bubbles does not
form in vacuum. Refer to the transformer
manuafacturers instructions.
Gas-saturated transformer oil
After the oil-filling process has been completed, wait
for 24 hours before energizing the transformer.
De-gassed transformer oil
After the oil-filling process has been completed, wait
for 6 hours before energizing the transformer.
A reduced oil-level
After the oil-level has been restored, wait 24 hours
before energizing the transformer.
