ABB BUE, Руководство по ремонту

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32 1ZSE 5492-129 en, Rev. 6
3.5 Examination of the diverter switch after a pressure relay trip
The pressure relay has tripped during normal operation.
3.5.1 Tools and material required
■
Maintenance guide for the on-load tap-changer in question
■ Lifting device as proposed in Maintenance guide
■
Sliding caliper
■
Rags (non-fuzzying)
3.5.2 Procedure
WARNING
Before any work is carried out on the on-load tap-changer:
Make sure that the transformer is disconnected and that earthing is properly carried
out. Obtain a signed certificate from the engineer in charge.
Close the valve to the oil conservator. Take off the cover of the diverter switch housing. The
oil level should be at least 50 mm below the upper edge of the housing. If the housing is
completely filled with oil or close to, the reason for the pressure relay trip is likely to be due
to this small or absent gas cushion.
Even if the gas cushion is small or absent,
the diverter switch should be lifted out of the
housing and be carefully investigated in order to exclude other reasons for the pressure relay
trip. Follow the procedure in section ”Lifting and cleaning the diverter switch” in the Mainte -
nance guide, when lifting the diverter switch.
Look for flash marks, loose parts etc. Measure the transition resistors according to section
”Checking the transition resistors” in the Maintenance guide. Finish with an
even number of
operations of the diverter switch according to section ”Checking the contact positions” in
the Maintenance guide. Make sure the diverter switch operates fast and distinct and stops in
the end positions.
If no faults are found, install the diverter switch according to section ”Installation of the di-
verter switch” in the Maintenance guide.
CAUTION
It is very important that the diverter switch is correctly installed. An incorrect installation will
jeopardize both the on-load tap-changer and the transformer!
If necessary according to above, restore the gas cushion according to section 3.3 ”Restor -
ing the gas cushion” in this guide.
Make sure the valve to the oil conservator is open!
After a pressure relay trip, we also recommend to carry out an insulation test and a ratio test
of the transformer.
If both the on-load tap-changer and the transformer are functioning properly, continue with
the next step.
3. Repairs and adjustments