Cleaning; Cleaning The Diverter Switch Housing; Cleaning The Oil Filter In The Conservator Pipe (If Any); Oil Filtration - ABB UC series Maintenance Manual

3.6 Cleaning

3.6.1 Cleaning the diverter switch housing

Clean the inner walls of the housing by means of a nylon
brush, then flush with oil. Drain the oil. Wipe the bottom and
inner walls with rags.
WARNING
In no case should any person go down into the
diverter switch housing. The cleaning of the diverter
switch housing should be carried out by using
brushes and rags and by flushing with oil.
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, the cleaning of the diverter switch is not
necessary.
Drain the housing completely by using a hose before oil filling
is carried out.

3.6.2 Cleaning the oil filter in the conservator pipe (if any)

The diverter switch housing and the oil conservator are
connected by a pipe. The diverter switch oil is contaminated
due to the arcing that occurs when the contacts operate.
In case of a common conservator with the transformer the
impure oil in the diverter switch housing must be prevented
from entering the oil conservator. An oil filter is therefore
mounted in the pipe.
The filter, which is mounted in a flange pipe on the top of the
diverter switch housing, is screwed from the inside. It can
easily be screwed out for inspection and cleaning.
The oil filter does not need to be replaced nor cleaned in any
other way than by washing with oil.

3.7 Oil filtration

The drained oil should be filtered until it is cleaned and has
regained the high dielectric strength required. The break-
down value for purified oil should be at least 160 kV/cm
according to IEC 60156,1995-08.
To check the result of the filtering, take test sample after the
oil has been filled into the on-load tap-changer.
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, no further oil filtration is necessary. Only
take an sample and measure the dielectric strength of
the oil, see section "Oil testing and oil draining" in this
guide.

3.8 Checking of the breathing device

Check the breathing device according to the instructions from
the transformer manufacturer.
WARNING
The breathers and the tube from the conservator
contains explosive gases. No open fire, hot surfaces
or sparks may be present when loosening the
breather.
1ZSE 5492-124 en, Rev. 6 | Maintenance guide UCG 17