WARNING
When oil that has been used in a diverter switch compartment is pumped out, con-
ducting tubes and hoses that are earthed should be used to avoid the risk of explo-
sion due to the gases produced by the arcs during service.
The oil in the diverter switch compartment may be hot. Be cautious!
There is always a cushion of explosive gases over the oil surface. This is sucked into
the on-load tap-changer tank during draining of the oil. No open re, hot surfaces or
sparks may be present when the top cover is opened.
CAUTION
Do not ll oil into the on-load tap-changer if the transformer tank is under vacuum and the
on-load tap-changer is not.
Do not ll oil into the transformer tank if the on-load tap-changer is under vacuum and the
transformer tank is not.
Leave a gas cushion on top of the oil in the diverter switch housing.
Take care to avoid ingestion of moist air when oil is drained. If the ambient air is moist, let
incoming air pass through a dehydrating breather with slow air ow to obtain proper dehy-
dration.
NOTE: Check the oil level one month after lling. It is usual for the oil level of the oil
conservator to fall due to gas absorption in the oil from the gas cushion in the diverter
switch housing, if the on-load tap-changer is not operated. Restore the gas cushion
and the oil level according to section 3.3.
Mounting of gaskets
CAUTION
Sealing surfaces and gaskets must be clean and undamaged. Diametrically opposed bolts
in sealing joints must be tightened alternately several times, beginning with a low tighten-
ing torque and nally with the recommended tightening torque as described in section 1.6
Tightening torque, in this guide.
After oil lling
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.
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