1. Remove all oil from the transformer.
2. Test new, unprocessed oil for
dielectric strength using ASTM Method D877. The oil must have a
minimum breakdown voltage of 30 kV.
3. After assembly, pressurize the
transformer to 2 psig by adding drynitrogen. Check the transformer
for leaks.
4. For transformers rated 115 kV and
above, after waiting for a 24 h period, make a dew-point check to
determine the dryness of the transformer insulation. For new
transformers and transformers in warranty, refer to the
manufacturer’s instructions for acceptable dew-point readings.
For transformers not in warranty, refer
to Table 8.1.5. If it does not pass dew-point test, a hot oil dryout
is required. After dryout, repeat step 4.
5. Draw a vacuum of 2 mmHg or less.
Hold this vacuum for a period of time specified in the manufacturer’s
instruction book, if the transformer is new or in warranty. If the
transformer is not in warranty, use Table 8.1.6.
6. Maintaining a vacuum of 2 mmHg or
less, admit oil into the top of the transformer connection. Once oil
filling is started, it must not be interrupted. Oil degassing
equipment is required for transformers rated 115 kV and above.
7. If the transformer is a conservator
type, stop filling when oil reaches a level 2 in. below the
transformer cover. If the transformer is equipped with a nitrogen
bottle, stop filling when the oil level gauge is slightly over the
25°C level. This is to compensate for the transformer expanding when
vacuum is broken and for oil cooling.
8. Break the vacuum with dry nitrogen.
If the transformer has a conservator with air bag, or air separation
membrane, add the remaining oil to the expansion tanks in accordance
with the manufacturer’s recommendations.
9. Bleed the air from transformer oil
pump vents. Turn on all pumps and leave them running while the oil
cools.
10. Allow the transformer to stand
before energizing (with oil pumps running) according to the timetable
shown in Table 8.1.7. Run one half of the pumps for half the time and
the other half of the pumps for the second half of the time.
11. Prior to energizing the
transformer, check oil levels in all compartments. Pump oil into the
top, if necessary, to raise the oil level to the 25°C mark.
12. Prior to energizing the
transformer, shut off all oil pumps and place controls on automatic
so that no pumps are running prior to energizing. This is important
to eliminate static electrification of the oil, which could cause an
internal failure. This hold time must be a minimum of 12 h.
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