Tightening Torques; Oil Filling; Oil Quality; Filling Methods And Restrictions - ABB VUBB User Manual

3.4 Tightening torques

The following tightening torques are recommended unless
otherwise stated in this user's guide:
M6 10 Nm ±10 %
M8 24.5 Nm ±10 %
M10 49 Nm ±10 %
M12 84 Nm ±10 %

3.5 Oil filling

3.5.1 Oil quality

The tap-changer contains about 300 liters of oil. The oil
quality should be LC set -30° according to IEC 60296:2012.
The oil should also comply with IEC 60422:2005.

3.5.2 Filling methods and restrictions

Oil filling can be carried out using one of the following
methods:
– At atmospheric pressure
– Under vacuum
The tap-changer housing is designed to for a vacuum on one
side and atmospheric pressure on the other.
CAUTION
The pressure difference between the inside and
outside of the housing may not exceed 100 kPa.
CAUTION
Be aware of the risk of slipping due to spilled oil.
The oil dissolves gases, especially if degassed oil is
used.
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3.5.3 Correct oil level

If possible, the oil levels of the oil conservators for the
transformer tank and tap-changer should be the same. The oil
level of the oil conservator for the tap-changer may never be
higher than the oil level of the transformer oil conservator.
At +20 °C, oil is filled to the level where the pointer on the oil
level indicator points half-way between MIN and MAX.
For temperatures other than +20 °C, proceed as follows:
– For every 10 °C increase of temperature, adjust the oil level
upwards a tenth of the scale range of the oil level indicator.
– For every 10 °C decrease of temperature, adjust the oil
level downwards a tenth of the scale range of the oil level
indicator.

3.5.4 Filling at atmospheric pressure

It is not necessary to perform steps 1 and 2 below. These two
steps are only described to speed oil filling. Oil filling can be
satisfactorily performed by only following steps 3 through 10:
1. Remove the inspection cover.
2. Pump in oil until it reaches the
3. Open the conservator valve, if any.
4. Remove the breathing device for the tap-changer
conservator.
5. Connect the pump to the oil valve on the tap-changer
cover.
6. Open the valve.
7. Pump in oil to the correct level. The oil level is shown on
the oil level indicator. (For correct oil level, see Section
3.5.3.)
8. Close the oil valve.
9. Disconnect the pump.
10. Refit the pipe or the breather. Make sure that the
connections are airtight – use sealing tape on the threads
and O-rings on the flanges.
CAUTION
Wait at least three hours before energizing the
transformer after filling oil at atmospheric pressure.
This waiting period is necessary to allow air bubbles
to dissipate.
mechanism.