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6Oil Filling
4. Let oil in through the oil valve of the on-load tap-changer. (For connection
dimensions, see the dimension drawing for the on-load tap-changer).
5. Shut the oil valve when the oil level in the oil conservator is correct at the actual
temperature, see even section 1.5.
6. When atmospheric pressure is restored in the transformer, remove the connection
between the two conservators and connect the breathing device to the oil
conservator for the on-load tap-changer. Make sure the connection to the
breathing device is properly sealed.
7. Restore the gas cushion in the diverter switch housing according to section 6.5.1
Restoring the Gas Cushion, procedure, point 1-6 and 9 in this guide.
6.5 Restoring the Gas Cushion
Check the oil level in the oil conservator one month after oil filling. If the oil level is
lower now than when the oil filling was finished (correct for temperature differencies!)
and no leakages are observed, the gas cushion has been solved in the oil and has to be
restored.
The procedure below is used for on-load tap-changers without oil filter unit for
continuous oil filtration. In case the on-load tap-changer is equipped with an oil filter
unit for continuous oil filtration from ABB, and it is installed according to our
recommendations, follow the instructions in Oil filter unit for on-load tap-changers,
manual for restoring the gas cushion.
CAUTION
To operate the on-load tap-changer with a too small or no gas cushion means a risk
for a trip of the pressure relay.
WARNING
The oil in the diverter switch housing may be hot. Be cautious!
WARNING
There is always a cushion of explosive gases in the top of the diverter switch
housing. No open fire, hot surfaces or sparks may be present during opening of the
housing or draining from the valve. After the cover is removed let the gas vent
away approximately 15 min before any work is started.
WARNING
Before any work is carried out on the on-load tap-changer:
Make sure that the transformer is disconnected and that earthing is properly
carried out. Obtain a signed certificate from the engineer in charge.
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