ABB UCL Installation And Commissioning Manual page 4

WARNING
Before carrying out work on the tap-changer, put
the LOCAL/REMOTE switch on the motor-drive
mechanism to position 0. It is also advisable to shut
the door of the motor-drive mechanism and pad lock
it when work is carried out on the tap-changer. The
key should be kept by the operator. This is done
to avoid an unexpected start of the motor-drive
mechanism.
WARNING
Before starting any work inside the motor-drive
mechanism, the auxiliary power must be switched off.
NOTE: The motor, contactors and heating element
may be energized from separate sources.
During drying of the transformer
CAUTION
The diverter switch should not be installed during
drying, since the process removes grease needed for
operation.
CAUTION
While drying with hot air and vacuum, the maximum
permitted pressure difference for the diverter switch
housing is 100 kPa at the maximum permitted
temperature of 135 °C (275 °F).
CAUTION
During drying with the vapor phase process, the cover
of the diverter switch housing and the bottom valve
should be left open. The valve is opened with the
special bottom valve key – a long hexagonal rod. The
maximum permitted temperature is 135 °C (275 °F).
CAUTION
Use the special bottom valve key only (delivered with
the tap-changer) to operate the bottom valve through
the oil draining tube. The use of a stiffer tool may
damage the valve.
CAUTION
To avoid seizing, do not operate the tap-changer
during the drying process or afterwards until it is filled
with oil.
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 tightening torque and finally with
the recommended tightening torque as described in
Section 1.8 Tightening torques in this guide.
During oil filling
WARNING
When oil that has been used in a diverter switch
housing is pumped out, grounded conducting
tubes and hoses should be used to avoid the risk of
explosion due to the gases produced by arcs during
service.
CAUTION
Do not fill the diverter switch housing with oil if the
transformer tank is under vacuum and the diverter
switch housing is not.
CAUTION
Do not fill the transformer tank with oil if the diverter
switch housing is under vacuum and the transformer
tank is not.
After oil filling
CAUTION
Do not energize the transformer earlier than three
hours after oil filling at atmospheric pressure. This
waiting period is needed to allow air bubbles to
dissipate.