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 T M 5-684/NAVFAC MO-200/AFJMAN 32-1082
(6) Install a t erminal connector of the proper
j. Ground sleeve. Inspection and repair of the
capacity.
ground sleeve includes the following steps:
m. Migration of compound. Inspecting and re-
(1) Check the condition of the ground strap
pairing compound migration should be made in the
that ties the metal sleeve to the supporting flange,
following manner:
and examine for tight connections.
(1) Check the oil and the bottom of the appara-
(2) Replace the ground strap if it is badly cor-
tus tank for visual evidence of compound leakage
roded.
caused by fractured porcelain or leaking gaskets.
(3) Tighten the connection.
(2) If much bushing compound has migrated
(4) Where a bushing is installed in liquid-filled
into the oil or the apparatus tank, replace the bush-
apparatus, see that the lower end of the bushing
ing with one of a modern design.
ground sleeve is immersed in the liquid at all times.
(3) Remove fluid from the apparatus tank.
A ground sleeve is intended to distribute voltage
(4) Clean the apparatus tank.
stress longitudinally along the bushing stem, thus
preventing the formation of corona above the liquid
(5) Refill with new or filtered fluid.
level.
n. Internal carbon deposits. Excessive accumula-
k. Bushing conductor lead. The following proce-
tion of carbon should be noted. Electrostatic flux
dures for inspection and repair are recommended:
causes free carbon in the oil to collect on porcelain,
(1) Look for deteriorated conductor lead insula-
herkolite, and/or micarta. Free carbon immersed in
tion, particularly where the lead leaves the bushing
oil will form frostlike figures that adhere tightly to
stem.
insulating materials. If enough deposit collects,
(2) Check the upper end of this type of bushing
flashover may result, particularly if moisture is
for evidence of corrosion where the conductor is
present. Therefore, carbon deposits should be wiped
soldered to the bushing cap.
off with suitable solvent, flushed with clean mineral
(3) Remove deteriorated conductor lead insula-
oil, and wiped with a clean lintless rag saturated
tion; inspect strands for mechanical condition, and
with clean oil.
retape with varnished cambric tape; then apply
o. Arcing gap. Arcing or coordinating gaps, if
l-inch (25 millimeter) linen tape, half-lapped to the
present, should be free from any obstructions and
required thickness.
the gap set at proper spacing.
(4) Paint with applicable Military Specification
p. Oil gage. Some bushings are provided with
MIL-V-173 varnish or other suitable insulating
means of indicating the level of the filler. Check
varnish.
these devices for proper operation and see that glass
(5) Clean bushing cap and porcelain surfaces
is not cracked or broken.
with soap and warm water, and swab out the tube.
q. Oil level. Inspect the oil level frequently. Low
(6) When replacing bushing conductor leads,
oil levels may be caused by overfilling or by oil being
braze or silver solder the leads and their terminal
forced up into any expansion chamber not equipped
connections.
with a core seal.
Line or bus connections. Inspection and mainte-
3-34. Bushing power factor tests.
nance should include the following steps:
The power factor of a bushing (or any other insula-
(1) See that connections are tight and free from
tor) is an indication of the effectiveness of the insu-
corrosion and dirt. Corrosion and dirt cause over-
lation to function properly. A low power factor (1
heating of terminals. Contacts that are not tight
percent or less) is an indication of good insulation.
result in corona discharge and arcing between loose
Because of differences in materials, a single power
points of contact and cause radio interference. An
factor test is of little value. However, a series of
energized connection suspected of overheating may
power factor tests allows the results to be compared,
be checked by fastening an unlighted tallow candle
on a disconnect pole, and observing whether or not
and a trend can be established. Increasing power
the candle melts when brought in contact with the
factors indicate deteriorating insulation and correc-
tive measures should be taken. Power factor testing
connection.
is recommended for bushings rated over 15 kilovolts
(2) Check for adequate rigidity and see that the
and for all bushings, regardless of voltage rating, in
connection design does not overstrain the porcelain
substations rated over 5,000 kilovoltamperes.
bushing. Check the foundation for movement.
(3) Check th e size of the terminal connector to
a. Schedule. Bushings should be power-factor
tested at the time of installation and at intervals as
ensure adequate current-carrying capacity.
given in table 7-l for transformers. Spare bushings
(4) Clean dirt and corrosion from connections.
should be -power-factor tested when received from
(5) Polish co tac surfaces with crocus cloth,
n t
the factory, and at approximately 2-year intervals
install new lock washers, and tighten bolts securely.
3-10
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