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3.15 Lubrication of the on-load tap-changer and the drive
shaft system
The bevel gears are greased at delivery and the same type of
grease is used for the couplings of the outer shaft system.
For access to the couplings, loosen the hose-clips and push
the protective tubes together. For access to the bevel gears,
dismount the covers.
WARNING
The bevel gear contains moving gears. Be cautious!
WARNING
Rotating shafts. Be cautious!
Check and lubricate with grease if necessary. Use standard
lithium complex or calcium complex grease with EP additive
NLGI 2. Temperature range from -30°C to +100°C. Suggested
products: Dow Corning Molykote Multilub, Gulf Crown EP 2 or
similar.
Remount the covers (make sure the gaskets are properly in
place).
3.16 Checking of the motor-drive mechanism
See the maintenance guide for the motor-drive mechanism.
3.17 Oil filling
If check of contact timing is to be carried out, see section
3.18, fill the diverter switch housing with oil up to the level
of the fixed main breaking contacts by easiest possible
method before checking. Oil fill completely according to the
instructions below after check of contact timing.
3.17.1 Filling methods and restrictions
Oil filling can be carried out at atmospheric pressure or under
vacuum. The wall between the diverter switch housing and
the transformer tank is designed to withstand vacuum on one
side and atmospheric pressure on the other side. It is not
allowed to have vacuum on one side and the pressure of an
oil column on the other side.
After maintenance oil is normally filled at atmospheric
pressure. This procedure is described in section 3.17.3. If
filling is to be carried out under vacuum, see the Installation
and commissioning guide.
After oil filling, a gas cushion should remain on the top of the
oil in the diverter switch housing.
22 Maintenance guide UCG | 1ZSE 5492-124 en, Rev 6
The connection to the oil conservator is designed to
automatically give a gas cushion when filling at atmospheric
pressure.
If new oil, especially degassed oil, is filled into the
diverter switch housing and the number of operations
is low, the gas cushion may be dissolved in the
oil. The oil level in the oil conservator should then
be checked after a month in service and if the oil
level is lower than after the oil filling, (corrected for
temperature differencies), the gas cushion should be
restored according to section 3.17.5 "Restoring the
gas cushion" in this guide.
3.17.2 Before filling
Oil filling may be carried out in different ways
depending on what is convenient as long as the rules
above are fulfilled and the on-load tap-changer is
filled with oil to the correct level with a gas cushion on
the top. The method below is recommended and if it
is followed in detail no pressure limits are exceeded
and oil levels and gas cushion will be correct. If the
on-load tap-changer consists of more than one unit,
fill one at a time.
3.17.3 Filling at atmospheric pressure
See Fig. 10.
1. Close the air release valve
2. Open the conservator valve, if any.
3. Dismantle the breathing device on the conservator for the
on-load tap-changer.
4. Pump oil into the diverter switch housing via the oil valve
(connection dimensions, see the dimension drawing for
the on-load tap-changer). Continue until the conservator
is filled to the correct level at the actual temperature. See
section 3.17.4. If there is more than one unit connected
to the same conservator, fill all of them until the oil level
indicator starts to move and fill up to the right level when
filling the last unit.
5. Shut the oil valve and disconnect the pump.
6. Remount the breathing device. Make sure the connection
to the breathing device is properly sealed.
3.17.4 Oil level
For correct oil level in the oil conservator, see the transformer
documentation.
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