Disconnection And Earthing Of The Transformer; Oil Volumes And Lifting Heights; Recommended Set Of Spare Parts; Oil Testing And Oil Draining - ABB UC series Maintenance Manual

3.3.2 Disconnection and earthing of the transformer

WARNING
Before starting any work in the on-load tap-changer
the protective motor switch and the LOCAL/REMOTE
switch must be set at 0.
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.

3.3.3 Oil volumes and lifting heights

The necessary number of empty drums for collecting and
filtering of the oil in the diverter switch housing should be
kept ready. The drums must be carefully cleaned and free
from water. New oil needed should be of class II according to
IEC 60296, 2012-02.
Quantity of oil in the diverter switch housing and lifting height for
the diverter switch
UCG.. 380/... Approx. 170 litres (lifting height 1.4 m)
UCG.. 650/... Approx. 170 litres (lifting height 1.4 m)
UCG.. 1050/... Approx. 205 litres (lifting height 1.7 m)
The volume of the oil conservator is not included.
Alternatively, the oil may be replaced by new oil and the used
oil filtered at some later occasion. A certain quantity of new
oil, at least 50 litres, should be kept ready to replace waste oil
and for cleaning.
CAUTION
Do not energize the transformer until oil has been
filled as per section 3.17 "Oil filling" in this guide.

3.3.4 Recommended set of spare parts

It is recommended to have a set of contacts for the diverter
switch available during the overhaul, see the spare parts list
for ordering.

3.4 Oil testing and oil draining

The diverter switch housing is equipped with an oil valve
placed on the top section. For connection dimensions, see
the dimension drawing for the on-load tap-changer.
WARNING
The oil in the diverter switch housing may be hot. Be
cautious!
Take an oil-sample from the oil valve and carry out the
dielectric strength test according to IEC 60156, 1995-08
(between spherical calottes, distance 2.5 mm). This test is
carried out for deciding whether the oil can be filtered or must
be exchanged.
The dielectric strength of the oil should not be allowed to be
less than 120 kV/cm for an on-load tap-changer in service.
When taking the oil-sample, first drain some oil into a
bucket to clean the valve.
If the oil conservator of the on-load tap-changer is common
with the oil conservator of the transformer tank, close the
valve in the pipe connection to the oil conservator and open
the oil valve. After a while, open the air release valve. See
Fig. 10.
CAUTION
Never block the hole in the draining tube!
If the on-load tap-changer is equipped with an oil
filter unit for continuous oil filtration from ABB and
it is maintained and operated according to our
instructions, oil draining and filtering is not needed,
provided that the dielectric strength is at least
160 kV/cm (IEC 60156, 1995-08).
There is a hole in the upper part of the draining tube
to prevent air from being trapped inside the tube
when oil filling. The air sucked in through this hole
when draining might disturb the function of some
types of pumps. In such case, drain the oil using a
hose instead.
1ZSE 5492-124 en, Rev. 6 | Maintenance guide UCG 15