Type 50-DH-50 Air Circuit Breaker
Supplementary Information
Recommended Maintenance For
ORGANIC INSULATION
Organic insulating materials are used in high
voltage air circuit breakers for pole unit supports,
operating rods, barriers, braces, arc chutes and
similar purposes, where it has been found to be
more suitable than porcelain. The material used
on Westinghouse breakers is Micarta, which has
a long established record for insulating and me
chanical dependability. To ensure long continued
electrical resistance, the Micarta surface is pro
tected with high grade insulating varnish which
may be either clear or pigmented, depending on the
place of use and the apparatus design require
ments.
The purpose of the varnish is to retard moisture
absorption and to provide an easily cleaned sur
face. Like all other insulating surfaces, whether
organic or inorganic, a varnished Micarta surface
should receive periodic attention in order to main
tain the insulation resistance at the highest possible
value.
The objects of maintenance are two-fold, first to
remove dust and other foreign air borne materials
as well as chemical oxides which· result from aging
of the varnish, and second to make sure that the
varnish provides a continuous protective film over
the entire insulating surface.
In addition to the usually recommended periodic
equipment inspections, on breakers that have been
in service for three to five years, the insulation
should be inspected, cleaned, and the varnish re
newed if the surface indicates it to be needed.
Cleanin�
While the surface of the insulation is dry, con
tamination does not usually cause any large change
in insulation value.
However, if while it is
present, moisture is added in the form of condensa
tion, or by more direct means, the surface electrical
leakage may be greatly increased, even to the point
of electrical breakdown. The first object of mainte
nance therefore is cleaning. A clean varnished sur
face will be smooth, glossy, and free from foreign
material either loose or adhering to the surface.
To obtain a clean surface, it is necessary to
loosen the adhesive dirt by scrubbing and washing.
This is best accomplished in the following manner:
1. Wash with normal heptane, obtainable from
the major oil companies such as Esso Standard.
Use clean paper towels wet in the heptane. Use
a
fresh towel on each part.
Caution: Heptane is inflammable and no open
flames or sparks should be allowed near the
work.
2. After the ·heptane has evaporated, which re
quires only a minute or two, wash with de-ionized
water, sometimes called demineralized water, or
distilled water.
Note: De-ionized or demineralized water can be
obtained in small quantities from many firms that
maintain chemical laboratories, particularly storage
battery manufacturers or electroplaters.
Use fresh paper towels and keep the water in a
handy size glass bottle. Wet the towel from the
bottle, wash the part and dry immediately with a
fresh towel. Use fresh towels for each part.
Inspection
When inspecting the insulating parts prepara
tory to cleaning, wipe off superficial dirt with a
dry cloth and note the condition of the varnish and
of the Micarta. If the varnish appears in good con
dition, i.e., fairly smooth and with liberal coverage,
proceed with cleaning.
If the varnish appears thin, and is not uniform in
coverage, is cracked, or can be peeled off with the
fingernail, the parts should be revarnished.
Varnishin�
Varnishing can be done with the parts in position
on the breaker, as follows:
1. Sandpaper when needed to remove loose var
nish and wipe off all dust from sanding.
2. Apply three coats of varnish, Westinghouse
M fl,
135-2. Allow 24 hours drying time between
coats at ordinary temperatures. Drying time may
be decreased by preheating parts with infrared
lamps to a temperature of 40 to 50 degrees C before
applying varnish and likewise heating each coat
for about 4 to
8
hours, or until the varnish has set
up to the point where it will not be lifted by apply
ing the succeeding coat.
Lamina
t
ed
I
n
su
la
t
i
o
n
Resin bonded laminated insulating materials are
formed under pressure at high temperature. The
release of pressure, reduction of temperature and
some further shrinking of the resin bond produces
internal stresses. Relieving of these stresses may
result in the formation of minute cracks or checks
along the laminated edges of the insulation. Such
cracks,
if
small, are sealed by the varnish and are
not harmful.
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