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7. Electrical connection and testing
7.1 General
Before the transformer is energized, tests must be carried out
to ensure that all mechanical and electrical connections are
correct, and to check the proper function of the motor-drive
mechanism and the tap-changer.
When testing the transformer, the tap-changer can be
operated either by the hand crank or electrically. When
operating electrically, the motor-drive mechanism is
connected according to Section 7.2.
WARNING
If 2 kV insulation testing is to be performed, some
equipment must be disconnected in order to avoid
damage. Examples of equipment to be disconnected
are the measuring transducer, pressure relay, diodes
(for example, N4) and temperature relays.
7.2 Connecting and testing the motor-drive mechanism and
the tap-changer
Connect the ground connection from the transformer to the
ground terminal on the tap-changer flange.
Connect the ground connector from the transformer to the
ground terminal on the motor-drive mechanism.
Connect the motor supply and the control supply to the
correct terminals on the motor-drive mechanism as shown by
the circuit diagram supplied with the tap-changer.
Operate the motor-drive mechanism by means of the hand
crank to a position at the middle of the range but not in a
through-position ( = a position with a letter in).
Turn the control selector switch to position LOCAL. Now send
a pulse for a RAISE operation.
If the phase sequence is wrong, (three-phase supply),
the motor-drive mechanism will start in the LOWER
direction.
The motor-drive mechanism will stop when it has
made approximately half of the complete operation
and will operate back and forth without the tap-
changer changing position until the control selector
switch is turned to position 0.
If the phase sequence is wrong, reverse two of the
motor supply cables to attain the correct sequence.
44 Installation and commissioning guide UCL/VUCL | 1ZSC000562-AAZ en
WARNING
Dangerous voltage!
For BUE: Run the motor-drive mechanism and check again
that the red mark on the brake disk stops within the tolerance
of ± 25° from the exact position; see Fig. 24.
For BUL: Run the motor-drive mechanism and check that the
center of the notch in the cam disk stops within ±2 mm from
the center of the roller on the brake arm; see Fig. 25.
For adjustment of the motor-drive mechanisms, see
Maintenance guide 1ZSC000498-ABH
Operate the drive mechanism electrically between the end-
positions. Check the end-stops. When attempting to operate
electrically beyond the end-position, the motor should not
be started. Check the mechanical end-stop by attempting to
hand crank it beyond the end-position. After a couple of turns
on the hand crank, it should be mechanically stopped. Hand
crank back to the end-position (where the indicator flag is
positioned at the middle for BUE and when the indicator flag
is white for BUL). Operate the tap-changer electrically to the
other end-position and repeat the test procedure above.
WARNING
The transformer must never be energized when the
end-stop is inoperable.
7.3 Electrical tests on the transformer
Acceptance tests on the transformer or commissioning can
now be performed.
7.4 After energizing
WARNING
Before any work is carried out on the tap-changer:
Make sure that the transformer is disconnected and
grounding is properly performed. Obtain a signed
certificate from the engineer in charge.
.
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