Howard Medium Power Substation - Manual (Page 8)

Document 2.4.06, Revision 4
June 2013 Medium Power Substation Transformers
STORAgE
Transformer Storage
Transformers can be stored if properly prepared. It is
recommended that stored transformers be completely
assembled. Prior to storage, transformers should be
pressure tested according to the instructions on Page
14 (Pre-energization Tests and Checklist). The gas
space above insulating fluid should be pressurized with
dry nitrogen to a pressure of between two to three PSIG.
This will prevent a negative internal pressure which
might draw moisture into the tank. Transformers not
designed for outdoor use must be stored indoors. If
the transformer is not completely assembled, separate
components and accessories should be stored in a
clean dry area in their original shipping containers.
Transformer fluid containers or totes should be covered
or stored in a protected area to prevent exposure to
rain water or other contaminants. Condenser bushings
should be stored in an upright position.
Extended Storage
If the transformer is to be stored for an extended period
of time before being placed into service, it should
be placed on a firm level surface. The following test
procedure should be used prior to storage (in addition
to following the Receiving Inspection instructions
on Pages 4 and 5 and Transformer Storage
recommendations on this page).
1. Measure and record ambient temperature and
barometric pressure (for correction of test data).
2. Pressure test the tank using the procedure on
Page 14 (Pre-energization Tests and Checklist)
and check for fluid leaks. Following pressure
test, reduce tank pressure to two (2) PSIG.
3. Test insulating fluid for dielectric strength and
moisture content.
4. Test insulation with a 1000-volt or 2500-volt
Megger test set. (Omit if bushings have not been
installed.)
5. Measure insulation power factor using Doble or
similar test set. (Omit if bushings have not been
installed.)
6. Measure coil ratios in each tap position to
ensure proper operation of the de-energized
tap changer. (Omit if bushings have not been
installed.)
7. Observe fluid level gauge to verify proper fluid
level.
Sidewall-mounted bushings, if exposed and not
contained in a terminal chamber or switch enclosure,
should be protected from moisture and ultraviolet
damage with an appropriate covering. This covering
should be checked periodically to ensure it is intact.
Cover-mounted bushings which are shipped separately
from the transformer should be stored in a clean,
dry location in their original shipping cartons. These
bushings should be carefully inspected for damage prior
to installation on the transformer.
All space heaters (if supplied) in terminal chambers,
switch cabinets, control cabinets or other enclosures,
must be connected and energized at all times to control
moisture. Desiccant packets may be used to control
moisture in control cabinets only, if it is not practical to
energize the control cabinet space heater. Desiccant
packets must be replaced periodically to maintain
effectiveness.
It is recommended that the transformer be inspected
periodically as described below while it is in extended
storage. Results should be recorded and compared with
previous results to ensure that no damage or change in
condition has occurred.
Quarterly Inspection
The quarterly inspection described below should be
performed after the first month of storage and then
quarterly thereafter.
1. Inspect protective covering on sidewall-mounted
bushings. Replace covering if damaged.
2. Inspect space heaters to ensure they are
working properly. Inspect desiccant packets (if
any) in control cabinets; replace if necessary.
3. Record fluid-level and pressure/vacuum
gauge readings. Ensure that tank pressure is
maintained at approximately 2 PSIG.
4. Measure and record ambient temperature and
barometric pressure.
5. If vacuum/pressure gauge or fluid level gauge
readings indicate a possible tank leak, perform
a tank pressure test according to instructions
found on Page 14 (Pre-energization Tests and
Checklist). Any leaks found should be repaired
immediately and then rechecked during
subsequent inspections.
6. Transformer fluid containers or totes should be
visually inspected for damage and any indication
of water intrusion or other contamination.
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