ABB UCL, Installation And Commissioning Manual

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Installation and commissioning guide UCL/VUCL

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1ZSC000562-AAZ en

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.

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.