WARNING
Be aware of the risk for slipperiness caused by oil spillage for instance when working
on the transformer cover.
The motor-drive mechanism must not be installed in any explosive atmosphere. The
electrical equipment creates sparks which can cause an explosion.
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.
Before carrying out work on the on-load tap-changer, put the LOCAL/REMOTE switch
in the motor-drive mechanism to position ”0”. It is also recommended to shut the door
of the motor-drive mechanism and pad lock it when work is carried out on the on-load
tap-changer. The key should be kept by the operator. This is done to avoid unexpect
-
ed start of the motor-drive mechanism.
Before starting any work inside the motor-drive mechanism, the auxiliary power must
be switched off.
N.B. The motor, contactors and heating element may be energized from separate
sources.
During drying of the transformer
CAUTION
During drying with hot air and vacuum, the maximum permitted pressure difference for the
on-load tap-changer is 100 kPa at a maximum permitted temperature of 135 °C (275 °F).
During drying by the vapour phase process the cover of the selector switch housing and the
bottom valve should be left open. The maximum permitted temperature is 135
o
C (275
o
F).
Use the special bottom key only (delivered with the on-load tap-changer) to operate the bot-
tom valve. The use of a stiffer tool may damage the valve.
Do not operate the on-load tap-changer during the drying process or afterwards until it is
filled with oil, to avoid seizing.
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 finally with the recommended tightening torque as described in section 1.7
Tightening Torque, in this guide.