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 TM 5-684/NAVFAC MO-200/AFJMAN 32-1082
in cap and assemblies, and a need for repainting.
thing that may result in an operating hazard. Frac-
Fractures and cracks are caused by deterioration of
tures or chips may be caused by the following ac-
cement, which allows the entrance of moisture that
tions.
(a) Rigid bus connections that do not allow
alternately freezes and thaws.
for thermal expansion or contraction.
f. Metal parts repair.
(b) Thrust from breaker operation, which
(1) Remove fractured, cracked, or defective
may fracture either the top or bottom porcelain if
clamping rings and hardware, and replace immedi-
the bottom member is loose.
ately.
(c) Uneven or excessive tightening of
(2) Wire brush spots down to bare metal, apply
clamping-ring bolts.
a priming coat of paint, allow to dry, and then add a
(d) Improper cementing onto the clamping
finish coat. Repaint periodically with a good
ring.
weather-resisting paint.
(e) Mechanical shock caused by blows or pro-
(3) Bushings that leak quantities of filler com-
jectiles.
pound or oil (especially at the clamping and mount-
(2) Contamination Check for foreign deposits,
ing flange assembly) should be removed from ser-
such as dirt, salt, cement dust, rust, carbon, acid oil
vice promptly and a replacement installed. These
sludge, filler compound, copper sulfate, or other ma-
conditions cannot be readily corrected in the field.
terial that may cause flashover under moist condi-
(4) Repairs that involve the baking out or
tions.
vacuum treatment of insulation, replacement of a
(3) Loose porcelain. Check for loose or improper
porcelain rain shield, or modernizing and rebuild-
seating of the lower porcelain.
ing, should be accomplished in a qualified service
(4) Evidence of flashover. Flashover may be
depot or manufacturer's shop. This work requires
caused by an operating voltage above the bushing
expert techniques, as well as special tools and
rating, excessive transient voltage, or semi-
equipment.
conductive foreign particles contaminating the por-
g. Cement inspection. The cement between
celain.
clamping rings, caps, and porcelain should be in-
d. Porcelain repair. In addition to the upper or
spected for crumbling or chipped surfaces and dete-
main body porcelain, some bushings have a lower
rioration that will permit the entrance of moisture.
porcelain member to give added strength against
Absorption of moisture and subsequent expansion
mechanical shock. Porcelain repairs generally are
and contraction, as a result of temperature changes,
made in either of the following ways:
hasten cement deterioration. Litharge and glycerin
(1) Fractures. When the main section of either
cement are particularly vulnerable.
the lower or upper porcelain is fractured, replace
h. Cement repair. It is often more economical and
the bushing. When the cause appears to be a too
desirable to replace rather than repair a deterio-
rigid connection, install a flexible connector or ex-
rated bushing.
pansion joint made from a flat strap, in addition to
(1) Make a temporary repair by cleaning porce-
replacing the bushing.
lain and painting the exposed cemented parts with
(2) Chips. When the main body of the porcelain
an insulating varnish in accordance with Military
is intact, but a crack is about to detach a large chip
Specification MIL-V-173.
of skirt, protect adjacent skirt and remove the chip
(2) Remove litharge and glycerin cemented
with a hammer. Smooth the sharp edges with an
bushings at the first opportunity and replace with
abrasive stone to prevent injury to workmen, and
bushings having mod.ern-type cement.
paint the exposed surfaces with a weather-resisting
(3) When loose cement permits movement of
material to provide a glossy finish that keeps out
porcelain, replace the bushing.
dirt and grit.
(3) Contam ination Remove deposits of foreign
i. Gasket inspection and repair. When inspecting
materials. Clean as recommended.
and repairing gaskets, look for leakage of filling
(4) Tracking. When there is evidence of flash-
materials, deterioration of gaskets, and improper
over, check the bushing voltage rating and surge
seating of gasket material (especially rubber-like
protection. Clean the bushings. Bushings experienc-
and cork composition). If quantities of filler have
ing frequent flashovers should be reported to the
leaked from the bushing, replace the bushing imme-
operating department, as this may require a review
diately. Cork exposed to moisture and air turns
of the application and associated surge.
dark, crumbles, and loses elasticity and binder. Re-
_
e. Metal parts inspection. Metal parts of bush-
place all deteriorated or improperly seated gaskets
with new gaskets as recommended by the bushing
ings, including the mounting flange and hardware,
manufacturer.
should be inspected for fractures, cracks, blowholes
3-9
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