Checking Oil Quality; Maintenance; Replacement Of The Complete Switching Mechanism Including Vacuum Interrupters - ABB VUBB User Manual

5. Check the oil level in the conservator. The level must
be as stipulated in the instructions from the transformer
manufacturer.
WARNING
The oil in the tap-changer housing may be hot.
Observe caution!
6. Check the breather according to the instructions from the
transformer manufacturer. If more than half of the drying
agent has changed color, it must be dried or replaced.
The drying agent normally starts to change color from the
bottom of the breather. If it changes color at the top of
the breather, there is a leakage in the connections to the
conservator. Locate the leakage and seal it.
WARNING
The breathers and the tube from the conservator
contain explosive gases. No open fires, hot surfaces
or sparks may be present when removing the
breather.

5.3 Checking oil quality

Check the quality of the oil according to IEC 60422:2005.
To simplify oil sampling, the transformer should have an oil tap
as shown in Fig. 65.
An oil filter unit is normally not required on the VUBB tap-
changer. But, if the tap-changer is equipped with an oil filter
unit from ABB, it should be inspected once a year.
Fig. 65 Oil sampling tap.

5.4 Maintenance

For maintenance, please contact ABB or make sure that
personnel performing maintenance are trained and certified by
ABB.
Maintenance of the tap-changer should be performed
regularly at intervals of 300,000 operations; see Table 2. The
relevant information is stated on the rating plate. This permits
confirmation of mechanical integrity and monitoring of contact
wear, and the necessary preparations can be made for
replacing the vacuum interrupters.
Table 2.
No. of operations Main activity
300,000 Maintenance (sequence measurement via
inspection hole on cover)
600,000 Replacement of switching mechanism (including
vacuum interrupters)
900,000 Maintenance (sequence measurement via
inspection hole on cover)
1,200,000 End of life
5.5 Replacement of the complete switching mechanism
including vacuum interrupters
The vacuum interrupters are sensitive and the settings must
be exact. It is thus important that replacement is performed
by an ABB-certified technician. Contact ABB or make sure
that personnel performing replacement of the complete
switching mechanism including vacuum interrupters are
trained and certified by ABB.
The estimated contact life of the vacuum interrupters in the
selector switch at rated load is stated on the rating plate of
the tap-changer. Also see Table 2.
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