ABB UCG Series, Installation And Commissioning Manual

Page: 25 / 56

1ZSC000562-AAZ en | Installation and commissioning guide UCL/VUCL 25
3.3 Connection to terminals
Connection to the tap selector should follow the connection
diagram supplied with the tap-changer.
In order to obtain maximum reliability for the tap selector
contacts, the temperature rise of the conductors connected
to the tap selector should be kept as low as possible and
should never be more than 30K above the surrounding oil.
CAUTION
All terminals must have conductors or connections,
including contact no. 30; see Fig. 9.
If there are connections between parallel conductors from
the diverter switch on the tap selector terminal, the parallel
conductors from the active part of the transformer should also
be connected on the tap selector terminals (in order to avoid
circulation currents through the tap selector contacts; see
Fig. 21).
If the impulse withstand voltage to ground exceeds 380 kV,
the conductor connections on the tap selector shall be
insulated by winding paper around them to a thickness of
3 mm; see Fig. 7. The paper should be of the same quality
as used for insulating conductors within the active part of the
transformer.
CAUTION
All connections should be made carefully and in such
a way that there is no risk that they can loosen. The
conductors must not cause mechanical strain on
the tap selector terminal. Each conductor should be
curved to take up expansion. See Fig. 20.
CAUTION
It is advisable that the distance between the cylinders
or the bars of the tap selector and any conductor
be at least 50 mm. The transformer manufacturer is
responsible for maintaining sufficiently large insulation
distances.
When yoke-mounted, inserts (wooden blocks, or
similar) are placed between the yoke fork and the
lower flange of the diverter switch housing (see
Fig. 21), so that the conductors can be mounted
at the correct height. The wooden blocks must be
removed before mounting the tap-changer on the
transformer cover.
Connection
Conductors from
active part of the
transformer
Tap selector
Conductors from
diverter switch
Connection
Fig. 19.