ABB UBBRT User Manual

40
1ZSE 5492-118 en, Rev. 4
7. Oil lling
7.1 Filling methods and restrictions
Oil lling can be carried out at atmospheric pressure or under vacuum. The wall between the
on-load tap-changer and the transformer tank is designed to withstand vacuum on one side
and atmospheric pressure on the other side. It is not allowed to have vacuum on one side
and the pressure of an oil column on the other side.
Oil lling may be carried out in different ways depending on what the transformer manufac-
turer nds convenient as long as the rules above are fullled and the on-load tap-changer is
lled with oil to the correct level.
The methods below are recommended and it they are followed in detail no pressure limits
are exceeded and oil levels and gas cushions will be correct.
After oil lling, a gas cushion should remain on the top of the oil in the selector switch hous-
ing.
The connection to the oil conservator is designed to automatically give a gas cushion when
lling at atmospheric pressure. When lling under vacuum a certain amount of oil has to be
drained in order to obtain the gas cushion. See section 7.5.
NOTE: The oil dissolves gases, especially if degassed oil is used. If the number of
operations is low, the gas cushion may be dissolved in the oil.
NOTE: If the transformer is lled at atmospheric pressure the air release valve on the
ange should be opened and the trapped air let out. Even better is to replace the air
release valve with a pipe to the gas operated relay.
7.2 Filling at atmospheric pressure
1. Open the conservator valve, if any.
2. Dismantle the pipe to the breather. Or, if simpler, take away the dehydrating breather.
3. Connect the pump to the oil valve on the on-load tap-changer cover. Open the valve
and pump in oil to the correct level shown on the oil level indicator. For correct oil level,
see section 7.4.
4. Shut the oil valve and disconnect the pump.
5. Reassemble the pipe or the breather. The connections must be airtight, use sealing
tape on the threads and O-rings in the anges.
When the transformer and the on-load tap-changer have a common oil conservator, a lter
in the connection between the on-load tap-changer and the conservator is needed.
1. The conservator valve should be shut.
2. Open the air release valve on the oil lter housing.
3. Connect the pump to the oil valve on the on-load tap-changer cover. Open the valve
and pump in oil. Stop the pump when oil reaches the air release valve.
4. Shut the oil valve and the air release valve and disconnect the pump.
5. Open the conservator valve.
NOTE: An appropriate gas cushion automatically remains under the top cover by
those methods.
CAUTION
Do not energize the transformer earlier than three hours after oil lling in atmospheric pres-
sure. This waiting period is needed to allow airbubbles to disappear.
7 Oil lling

ABB UBBRT Specifications

General

Brand	ABB
Model	UBBRT
Category	Industrial Equipment
Language	English