Procedure - ABB UZE Repair Manual

3 Repairs and adjustments

3.1.4 Procedure

If the transformer is located outdoors the on-load tap-changer must be protected against
rain.
1.
2.
3.
NOTE: Be careful with the gasket when removing the cover.
4.
5.
6.
7.
NOTE: If a stud bolt is broken, the rest has to be drilled out and the hole has to be
rethreaded (M16).
8.
9.
10. Remove the old gasket from the board and the phase unit. Use solvent and a chisel to
11. Before mounting new stud bolts, (if necessary) brush grease onto 4-5 of thread turns to
12. Test assemble the distance pieces, t = 9 mm, between the clamp screws and the
13. Mount the phase unit in the following way:
20
Lower the oil level in the transformer to a level below the on-load tap-changer. Refer to
the documentation for the transformer.
Drain the oil from the on-load tap-changer. Use the pump and clean, empty, drums.
The on-load tap-changer must be empty before the repair procedure is continued. For
information about oil draining, see the Maintenance Guide.
Open the front cover by loosening the domed nuts (19 mm).
Wash the tank clean with oil by using a hose and a pump. After washing, the inside of
the tank and the phase units should be wiped clean with rags (not cotton waste).
Mark the shafts to make it possible to remount them in their right place and so that they
will get the ends in the same position as before. Dismantle the shafts on both sides of
the phase unit by loosening the screwed couplings on the left hand side of each shaft.
Take care of shims, if any.
Disconnect the conductors of the transformer side of the phase unit. On UZF through
the connection cover on the roof of the tap-changer tank. On UZE through some man-
hole on the transformer.
Unscrew the nuts of the clamps that holds the phase unit.
The phase unit now stays in place by the glued gasket. Make some arrangement in
order to prevent it from tilting out when coming loose from the board, e.g. by using a
rope between the phases.
Loosen the phase unit by wedging between the moulding and the board. Use wooden
wedges.
Place wedges, one in each of the upper corners between the gasket and the board, by
some light beats. Wet the glued gasket with ethylacetate or similar solvement to dis-
solve the glue. The epoxy moulding is wedged to come loose by gradual wedging and
wetting the glue. Do this carefully and give the solvent time to dissolve the glue. If this is
done too quickly, there is a risk of breaking the moulding or the board.
remove all residues of the gasket and make the surfaces quite free from glue and oil.
Also wash the surrounding surfaces with solvent to make sure that the surfaces to be
glued will remain dry during the gluing process.
be screwed into the board.
Mount the stud bolts. Screw until stop. Don't use a higher tightening torque than 5 Nm.
moulding, and fasten them temporarily to the screws with tape. The distance pieces are
used for guiding the phase unit when glued to the board.
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Clean the surfaces with the solvent immediately before gluing.
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Glue should be spread over both sides of the gasket at least 8 hours before final
gluing.
CAUTION
1ZSE 5492-128 en, Rev. 4