ABB BUL2 Manual do utilizador - Página 6

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Inspection

CAUTION

Approval should be given by the site engineer in

charge for inspection as well as for operating the tap-

changer.

It is recommended to inspect the tap-changer once a year.

This principally concerns the motor-drive mechanism and

refers to a visual inspection inside the BUE/BUL cabinet to

check that nothing is loose, and that the heater is functioning.

In the motor-drive mechanism a counter registers every tap-

change operation. During inspection the counter is read and

noted. If possible, motor and counter are to be tested by

operating one step and then back.

If the tap-changer has its own oil conservator, the breather

and the oil level indicator on the oil conservator are to be

checked according to the instructions from the transformer

manufacturer.

The inspection is to be carried out while the transformer is in

service.

On the conservator the following are to be checked:

– Oil level

– Breather

In the motor-drive mechanism the following items are to be

checked:

– Motor and counter

– Emergency stop

– Heater

– Earth fault protector for the outlet (option)

If the tap-changer is equipped with an oil filter unit, the

pressure drop over the filter is to be checked.

Required tools

The following eq uipment is required for the inspection:

– Set of screwdrivers

– Pen and note pad

6 User's manual UBB | 1ZSE 5492-156 en, Rev. 4

Procedure

WARNING

Checking of the breather and the oil level must be

carried out from ground level since the transformer is

energized.

1. Checking of the breather

WARNING

The breathers and the tube from the conservator

might contain explosive gases. No open fire, hot

surfaces or sparks may be present when removing the

breather.

Check the breather according to the instructions for the

transformer.

If more than half of the drying agent has changed colour, it

must be dried or replaced.

The drying agent usually starts to change colour from the

bottom of the breather. If it changes colour at the top of

the breather, there is a leakage in the connections to the

conservator. Locate the leakage and seal it.

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.

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 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.