ABB UC User Manual - Page 7

Browse online or download pdf User Manual for Industrial Equipment ABB UC. ABB UC 12 pages. On-load tap-changers

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Procedure

Checking of the breather and the oil level must be carried out from ground level since the trans-

former is energized.

1 Checking of the breather

Check the breather according to the instructions for the transformer.

The breathers and the tube from the conservator contains explosive gases. No open fire, hot surfaces

or sparks may be present when removing the breather.

2 Checking of the oil level in the conservator

The oil level in the conservator should be according to the instructions in the transformer

documentation.

If the oil level, corrected for temperature differencies at the different reading occasions, has became

lower and no leakages are observed, the gas cushion on top of the oil in the diverter switch housing

has been dissolved in the oil.

Call a specialist for restoring the gas cushion. Prepare for the outage of the transformer during the

restoring.

NOTE: In case the on-load tap-changer has an oil filter unit from ABB that is installed according to

our instructions, no outage of the transformer is necessary.

To operate the on-load tap-changer with a too small or no gas cushion means a risk for a trip of the

pressure relay.

3 Checking of the motor and the counter

Open the motor-drive cabinet door and turn the selector-switch to the LOCAL position. Then turn the

control switch to the RAISE (LOWER) position.

Check that the motor works properly, the position indicator increases (decreases) one step, and the

counter advances one step for each operation. Record the counter's value. The counter shows the

number of operations run by the on-load tap-changer (the overhaul schedule can be determined with

the help of this information).

Turn the control switch to the LOWER (RAISE) position. Check that the motor also works properly in

that direction, the position indicator decreases (increases) one step and the counter advances one step

more.

Reset the draghands.

4 Checking of the emergency stop

Give a RAISE or LOWER impulse and after about one second press the emergency stop. The operation

should be interrupted. Reset the emergency stop by turning the knob clockwise and set the protective

motorswitch to ON. The started operation should now be completed. Operate back to service position.

WARNING

CAUTION