GE Industrial Solutions Seconday Substation Transformer - Manual (Page 3)

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attempting to loosen and remove manhole
cover.
A. INSULATING LIQUID
Before opening a transformer, take samples
of the insulating liquid from the top and
bottom of tank and test the dielectric
strength. The dielectric strength should be
no less then 27.5 kV. If it is lower, the
transformer should not be placed in service
until the dielectric strength has been restored
by filtration.
B. CORE-AND-COIL ASSEMBLY
Lower the insulating liquid to the top of the
core-and-coil assembly and inspect the
interior to see if any damage has occurred. If
possible, DO NOT allow the coils and
insulation to be exposed to the air.
Examine the top of the core-and-coil
assembly, all horizontal surfaces and the
underside of the cover for signs of moisture.
If there are no signs of moisture or damage,
proceed with the
reassembly of the
transformer. If there are signs of moisture
inside the tank, steps should be taken to
determine the extent of it and the manner in
which the moisture entered the transformer.
Reassembly should be carried through and
the manufacturer of the equipment should be
requested to make recommendations
concerning further checks and steps for
drying out the transformer.
If the transformer appears to have been
damaged internally, or if it is desirable to
remove the core-and-coil assembly for
inspection or drying, the transformer may be
untanked as follows:
1. Remove the handhole lid and
disconnect high-and low-voltage
leads if the bushings are in position.
Remove large bushings from cover if
any.
2. Small bushings if any may be left on
the cover if they are protected and
the cover is carefully handled.
Remove cover. Remove
thermometer, tap changer and liquid
gauge and all other accessories and
associated wells which project into
the tank and which might interfere
with untanking operations.
3. Use slings for removing the core-and-
coil assembly.
4. Particular care must be taken in
handling tools and other loose
articles when working with a
transformer. Metallic objects, if
dropped in the windings and allowed
to remain there, can cause a severe
fault.
STORAGE
It is advisable to locate a transformer,
complete with liquid, in its permanent location
even if it will not be placed in service for some
time. It is recommended to check the paint
finish and to repair all damaged painted
surfaces. If the transformer is shipped and
stored in dry inert gas, the gas pressure
should be maintained and periodically
tested. If an oil-filled, indoor-type transformer
is stored outdoors, it should be thoroughly
covered to keep out rain. A transformer
should not be stored or operated in the
presence of corrosive vapors or gases, such
as chlorine.
Should it become necessary to store
accessories for a long period of time, they
should be stored in a clean, dry place or the
manufacturer should be contacted for explicit
instructions on the storage of individual
pieces.
LOCATION
Accessibility, ventilation and ease of
inspection should be given careful
consideration in the location of transformers.