Howard HI-104 Single-Phase Pad Transformer - Manual (Page 30)

Document 2.4.96, Revision 0
March, 2013
30
Single-Phase Pad-Mounted Compartmental-Type Distribution Transformers
4. Fluid quality tests, such as moisture content,
power factor, dielectric strength and dissolved gas
analysis.
Exterior Paint Finish
Any damage to the exterior paint finish that exposes
the primer coat or bare metal should be repaired
immediately in order to prevent corrosion. Areas
to be repaired should be thoroughly clean and dry.
The surface should be sanded to remove rust, loose
paint flakes and other debris. The surface should
then be cleaned with a suitable solvent to remove
any oil, grease or other contaminants. At lease two
coats of high-quality touchup 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 Trans-
former Division.
Fluid Leaks
Check the tank for indication of fluid leaks, looking
carefully at weld seams and at tank fittings, such
as bushings, gauges, plugs and valves. 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 trans-
former. False indications of a leak can occur as a re-
sult of residual fluid that was not sufficiently cleaned
after the transformer was filled with fluid. In some
cases silicone lubricant used to install high-voltage
bushing inserts can flow onto the front panel, giving
a false indication of a fluid leak.
In addition to the presence of fluid residue, a low
reading on the optional fluid level gauge and a con-
stant zero reading on the optional pressure/vacuum
gauge (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 sus-
pected 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 nitrogen through
the pressure test 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 to all
welds, joints, pipe fittings, and cable connections.
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 panel-type radiators is not
recommended due to the thin gauge material used
in its construction. Very small pin-hole leaks can
sometimes be repaired using an epoxy patch kit
designed to repair fluid 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 hum-
ming 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 condi-
tions at the installation site. Unusual sounds should
be investigated, as this might indicate a potential
problem.
Refer to NEMA Standards Publication TR-1 Trans-
formers, Regulators and Reactors, and IEEE Stan-