24
1ZSE 5492-118 en, Rev. 4
4. Drying
A drying agent is placed inside the package to keep the on-load tap-changer dry during
transport. It is not necessary to dry the tap-changer if the package not have been destroyed.
The on-load tap-changer can be dried together with the transformer according to one of the
following processes: alternating hot-air and vacuum or vapour-phase at a temperature of
max. 135 °C (275 °F) and a maximum pressure difference of 100 kPa between tap-changer
and transformer.
4.1 Observations before processing
1. When drying with the vapour-phase process the bottom valve of the on-load tap-
changer shall be open and the cover of the on-load tap-changer, the O-ring and the
sealing of the suction pipe shall be removed. See section 3.2.2, point 1. To open the
bottom valve, proceed as follows:
2. Use the delivered bottom valve key to engage the internal hexagon hole of the bottom
valve. Open the valve by turning anticlockwise max. 4 turns.
3. When drying in a vacuum pan with the hot-air process, the top cover of the on-load
tap-changer, the O-ring and sealing of the suction pipe shall be removed. See section
3.2.2, point 1.
4.2 Observations after processing
CAUTION
To avoid seizing, do not operate the on-load tap-changer, neither during the drying process
nor afterwards, until it is filled with oil.
1. Make sure that all liquid has been drained from the selector switch housing. Close the
bottom valve. Tightening torque is approximately 15 Nm.
2. If a tie-in resistor from ABB is supplied, its screw joints are to be retightened (tightening
torque 15 Nm) and locked by the method specified by the transformer manufacturer.
4 Drying