Yoke-Mounting - ABB UCL Installation And Commissioning Manual

3.2 Yoke-mounting

(Pre-mounting on active part of the transformer.)
The top section of the diverter switch housing is designed
to be divided into an upper and a lower flange (see Figs. 11
and 13) to fit the yoke-mounting.
Before lifting and joining the diverter switch housing to the
transformer cover, it is placed on a yoke fork (two beams) that
is fastened on the upper transformer yoke; see Fig. 10.
The guide pins used on the yoke fork should be
insulated with bushings in order to prevent circulating
current in the yoke fork when the transformer is in
operation.
Mounting of the tap-changer on the yoke fork can be carried
out by two alternative methods depending on when the
transformer ratio measurement is carried out:
– Transformer ratio measurement is carried out before the
drying process; see Section 3.2.1.
– Transformer ratio measurement is carried out after the
drying process; see Section 3.2.2.
For mounting on the transformer cover after the drying
process; see Section 3.2.3.
CAUTION
To avoid seizing, do not operate the tap-changer,
neither during the drying process nor afterwards, until
the diverter switch housing is filled with oil and the tap
selector is immersed in oil.
Bevel gear
On-load
tap-changer
Fig. 10. Yoke-mounting principle.
1ZSC000562-AAZ en | Installation and commissioning guide UCL/VUCL 19
Transformer
active part
Yoke fork