ABB Power Grids Ltd.
GKSL 680205.021 RE
Rev. 2, 26.09.2019
8
crane. The other sling is fixed around the two uppermost porcelain sheds and attached to the same lifting
hook. The angle is adjusting by the polyspast.
7.2 Installation on the transformer
The bushings type BRIT do not contain transformer oil and therefore can be mounted right after transporting
or storage without being kept upright for a certain period.
7.3 Cleaning the bushing surfaces and interfaces
The sealing faces on the transformer tank and at the bushing flange must be free from corrosion and
contamination and offer a high surface finish (max. Ra 3.2). Clean these sealing faces by soaking a lint-free
cotton cloth in the cleaning liquid and wiping them off.
Always make sure that the vent hole at the flange is not obstructed or closed e.g. by a flat seal.
The unshielded area of the bushing (insulating body at oil side) may not be scratched. If the lifting eyes at
the bottom of the flange protrude, they must be dismounted before tightening the flange. The fastening of
the flange must be designed in a way that no deformation may occur at the bushing flange. The support
surface of the transformer must have a flatness tolerance of max. 0.3 mm (no steps allowed).
Before the installation, the bushing must adapt to the environmental temperature to prevent condensation
at the bushing surface.
Warning! Do not damage the sealing face!
7.4 Tightening order and tightening torques
Tightening order and tightening torques
After the bushing flange has been seated, the screws / nuts must be tightened by hand as far as possible in
a first step. Fastening the flange must be done by observing the following tightening sequence:
1. Light fastening using screw wrench.
2. Fastening up to 25% of the recommended torque.
3. Fastening up to 75% of the recommended torque.
4. Fastening up to 100% of the recommended torque.
5. Further tightening sequence for inspection using 100% of the recommended torque.
6. If possible, repeat steps 4 and 5 after 24 hours as the pretensioning force may weaken within the first 24
hours.
So that no screw / nut is forgotten, the tightened screws / nuts are to be marked using a felt pen dash.
