Howard HI-102 Overhead Transformer - Manual (Page 24)

Document 2.4.95, Revision 0
May. 2013
24
Fluid-Filled Overhead Distribution Transformers
paint flakes and other debris. The surface should
then be cleaned with a suitable solvent to remove
any oil, grease or other contaminants. At least two
coats of a high-quality touch-up paint should be
applied to the damaged area. Bare metal should
receive a primer coat before applying the final
finish. Touch-up paint is available from the Howard
Industries Transformer Division.
Fluid Leaks
Check the tank for indication of fluid leaks, looking
carefully at weld seams, bushings and all tank
fittings. Fluid leaks should be repaired as soon as
possible to prevent moisture contamination of the
insulating fluid and to prevent internal flashover due
to low fluid level.
▲
! WARNING
FAILURE TO FOLLOW THE INSTRUCTIONS
BELOW COULD RESULT IN DEATH OR SERIOUS
PERSONAL INJURY, AND COULD ALSO RESULT
IN DAMAGE TO THE EQUIPMENT.
• De-energize transformer from a remote
location before performing any inspection or
maintenance work.
• Make sure all transformer terminals and
bushings have zero voltage.
• Make sure that the transformer is properly
grounded.
• Fluid leaks should be repaired as soon as
they are discovered.
If a fluid leak is suspected, investigate thoroughly
to determine if an actual leak does exist on the
transformer. False indications of a leak can occur
as a result of residual fluid that was not sufficiently
cleaned after the transformer was filled with fluid.
In addition to the presence of fluid residue, a low
reading on the fluid level gauge, if present, and a
constant zero reading on the pressure/vacuum
gauge, if present, (which does not vary over time
as a function of transformer loading and ambient
temperature) are also indications of a possible fluid
leak.
To verify that a fluid leak does exist, clean the
suspected leak area with an appropriate solvent
to completely remove the fluid and observe the
area for reappearance of fluid. To accelerate the
test, pressurize the tank with dry air or dry nitrogen
through the PRV fitting to a pressure of 3-4 PSIG. Let
the tank stand under pressure for one to two hours,
then inspect for leaks. Leaks above the fluid level
can be detected by applying soap solution prior to
the pressure test.
In many cases a small pin-hole tank leak or leak
from a bushing, gauge, valve or other fitting can be
repaired on site. Pin-hole and weld seam leaks can
usually be repaired by welding on a de-energized
transformer. Welding on radiator panels is not
recommended due to the thinner gauge material
used. Very small pin-hole leaks can sometimes be
repaired using an epoxy patch kit designed to repair
oil leaks.
Bushing leaks can sometimes be corrected by
tightening the bushing clamp bolts. Do not exceed
the recommended torque values listed in Table 2 to
prevent the possibility of bushing or gasket damage.
Audible Sound Level
It is normal for transformers to emit an audible
humming sound, which is primarily caused by
alternating magnetic flux in the transformer core.
Amplitude and harmonic content of the sound is
influenced by transformer size, the energizing voltage
level and sinusoidal purity, load conditions and
acoustic conditions at the installation site. Unusual
sounds should be investigated, as this might indicate
a potential problem.
Refer to NEMA Standards Publication TR1,
Transformers, Regulators and Reactors, and IEEE
Standard C57.12.90, IEEE Standard Test Code for
Liquid-Immersed Distribution, Power, and Regulating
Transformers for more information about design
sound levels and factory sound testing.
Low-Voltage Circuit Breaker
The low-voltage circuit breaker, if present, is
accessible by removing the transformer cover or
handhole cover. The link to the operating handle
can be adjusted if necessary for proper operation.
Defective breakers should be replaced. Refer to
“Opening the Transformer Tank” for instructions.