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 TM 5-684/NAVFAC MO-200/AFJMAN 32-1082
3-22. Cleaning of insulators.
provide a glossy finish and to lessen dirt accumula-
tion.
Since the insulating qualities of insulators, and
(c) Since the loss of a skirt on a pin-type
their ability to prevent flashovers, depend on pre-
insulator reduces the insulation value of the insula-
venting contamination buildup, cleaning fre-
tor by 30 percent or more, replace such broken
quencies will depend on the location. Ceramic insu-
units.
lators must maintain their glass-like glaze and care
b. Nonceramic insulators. Nonceramic or compos-
must be taken in cleaning to prevent this smooth
ite insulators include core, weathersheds, and
surface from being scratched or dulled. Nonceramic
metal-end fittings. A weathershed is the external
insulators will deteriorate with time as the surface
part of the insulator that protects the core or me-
decomposes, although proper cleaning will help to
chanical load-bearing component and provides the
extend their service life. For convenience, safety
wet electrical strength and leakage distance. The
and thoroughness, insulators should be cleaned
core consists of resin and glass fibers. The
while out of service.
weathersheds are of polymeric materials such as
epoxy resins or elastomers and normally contain
a. Causes of contamination. All insulators and
inorganic fillers.
also bushings are designed to permit satisfactory
(1) Construction.
operation with some contamination. However, alter-
nate wetting by early morning mist and fog, fol-
manufactured with rods of fiberglass treated with
lowed by exposure to dust and wind, can build up
epoxy resins. Rubber-like compounds are applied to
harmful deposits. Special contamination problems
the rods to fabricate suspension, dead-end, and
are encountered near steel mills, cement and chemi-
post-type insulators.
cal plants, and other factories that saturate the air
(b) Polysil. Polysil insulators are formed by
with finely divided, semi-conductive particles. Along
using various sizes of silica bound together chemi-
coastal areas, salt deposits build up and materially
cally with a resin into a compound which is approxi-
reduce the flashover value. Many of these deposits
mately 90 percent silica. Insulators have excellent
are extremely tenacious, requiring that the insula-
mechanical and dielectric strength, are nontrack-
tor be removed from service and cleaned by hand.
ing, and do not carbonize under severe arcing con-
Where contamination is serious, special long-
ditions. They are very durable for use in an adverse
leakage suspension insulators for high-voltage lines
atmosphere. Polysil was developed by the Electric
have been used; but, where severe deposits occur,
Power Research Institute (EPRI).
washing of special insulators is required as often as
(2) Inspection and replacement. Composite in-
for standard insulators. To lengthen maintenance
sulators are frequently used in outlying areas
intervals, in areas where contamination is severe,
where shooting vandalism is a problem. Damage to
ceramic insulators and bushings may be coated
nonceramic insulators, particularly from small
with special silicone greases. Greasing is not recom-
arms ammunition, may not always be easily de-
mended for nonceramic insulators, a channeled arc-
tected visually. When such damage is detected, the
ing can lead to tracking on greased composite insu-
damaged insulators should be replaced as soon as
lators. Many weathershed materials are unsuitable
practical, especially if embedded metal is found in
in areas where hydrocarbon vapors are prevalent or
the shank of the insulator. A few holes through only
where they come in contact with wood poles treated
the weathersheds will have little or no adverse ef-
with hydrocarbons.
fect on the performance of the insulator.
b. De-energized cleaning methods and materials
c. Metal parts. Metal parts consist of fittings that
connect the insulator at one end to the support and
methods are specified for porcelain cleaning. Table
at the other end to the conductor.
3-2 should also be consulted.
(1) Inspection. Look for fractures and any rust.
(1) Clean, grit-free, lintless wipers should be
(2) Repair insulators having defective hard-
used.
ware.
(a) Wire-brush rusty spots down to bare
(2) An abrasive, of the kitchen-cleanser type,
metal. Apply priming coat of paint and dry. Apply
mixed with clear water to the consistency of a thick
finish coat of paint to spots covered with primer.
paste, may be applied with a wiper or stiff-bristle
(b) Replace insulator if loose cement permits
brush. The amount of rubbing depends on the ma-
movement between porcelain and metal parts.
terial being removed. Rinse freely with clear water.
3-5
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