increase in power factor should be
questioned and scheduled for removal
from service. Measured power-factor
values should be temperature corrected to
20
questioned and scheduled for removal
from service. Measured power-factor
values should be temperature corrected to
20
E
2. The RIV test.- The RIV test can provide
detection of corona in resin- bonded, solid-
core noncondenser bushings. Methods of
measurement of RIV are described in
NEMA Publication No. 107. Copies of this
publication may be obtained from D-8440
or D-8450.
detection of corona in resin- bonded, solid-
core noncondenser bushings. Methods of
measurement of RIV are described in
NEMA Publication No. 107. Copies of this
publication may be obtained from D-8440
or D-8450.
Liquid-filled bushings generally have a low
RIV value. A high RIV value on this type of
bushings which cannot be reduced by
cleaning the porcelain indicates the level
of the filling liquid should be checked.
RIV value. A high RIV value on this type of
bushings which cannot be reduced by
cleaning the porcelain indicates the level
of the filling liquid should be checked.
3. The dc insulation resistance test. The
dc insulation resistance test generally
cannot be relied on to detect early con-
tamination in bushings. When bushing de-
terioration can be detected by dc insulation
resistance, it is generally in an advanced
stage requiring immediate attention. A
2500-volt insulation resistance meter
may be used for an insulation resistance
check, but a high reading should not be
completely relied upon as indicating a
good bushing. Any bushing testing less
than 20,000 megohms has questionable
insulating value.
dc insulation resistance test generally
cannot be relied on to detect early con-
tamination in bushings. When bushing de-
terioration can be detected by dc insulation
resistance, it is generally in an advanced
stage requiring immediate attention. A
2500-volt insulation resistance meter
may be used for an insulation resistance
check, but a high reading should not be
completely relied upon as indicating a
good bushing. Any bushing testing less
than 20,000 megohms has questionable
insulating value.
4. Hot-wire test for moisture.- Plastic
type compound used in compound filled
bushings may absorb moisture if there are
leaks through the shell or cap. A moisture
content of as little as 0.15 percent in soft
compounds can be detected by pushing a
red-hot rod into the compound. If moisture
is present, a crackling, sputtering, or
hissing sound will be heard. If no moisture
is present, the compound will melt quietly.
Another test is to put some compound on
type compound used in compound filled
bushings may absorb moisture if there are
leaks through the shell or cap. A moisture
content of as little as 0.15 percent in soft
compounds can be detected by pushing a
red-hot rod into the compound. If moisture
is present, a crackling, sputtering, or
hissing sound will be heard. If no moisture
is present, the compound will melt quietly.
Another test is to put some compound on
a wire and melt it in the flame of a match. If
moisture is present, there will be a sputtering
sound and small sparks will be thrown off. Dry
compound will melt without disturbance.
moisture is present, there will be a sputtering
sound and small sparks will be thrown off. Dry
compound will melt without disturbance.
5. Testing oil for moisture. - Whenever
the presence of moisture in the oil of an oil-
filled bushing is suspected or found by a
bushing power-factor test, the oil should be
drained out and a sample tested by a
dielectric or power-factor test. Since the
quantity of oil in a bushing is small, the old
oil should be discarded and new oil put in. If
moisture is found in the oil, the bushing
should be dried out before returning to
service.
the presence of moisture in the oil of an oil-
filled bushing is suspected or found by a
bushing power-factor test, the oil should be
drained out and a sample tested by a
dielectric or power-factor test. Since the
quantity of oil in a bushing is small, the old
oil should be discarded and new oil put in. If
moisture is found in the oil, the bushing
should be dried out before returning to
service.
V. Storage of Bushings
The manufacturer's instructions for storage should
be followed for all bushings. The following are
general guidelines for the storage of bushings:
be followed for all bushings. The following are
general guidelines for the storage of bushings:
A. Bushings should be stored where they
will not be subject to mechanical damage.
will not be subject to mechanical damage.
B. Bushings having exposed paper insulation
on the lower end require special protection to
prevent moisture contamination. This can be
accomplished with a tank or tub filled with oil
or with a special moisture- proof wrapping.
Completely sealed outdoor bushings may be
stored out of doors.
on the lower end require special protection to
prevent moisture contamination. This can be
accomplished with a tank or tub filled with oil
or with a special moisture- proof wrapping.
Completely sealed outdoor bushings may be
stored out of doors.
C. Liquid- and plastic-filled bushings
should never be stored in a horizontal
position. Storage in a horizontal position can
introduce voids or air bubbles into the filler
insulation.
should never be stored in a horizontal
position. Storage in a horizontal position can
introduce voids or air bubbles into the filler
insulation.
The condition of stored bushings should be
checked periodically for oil level, mechanical
damage, and power factor as described in section
IV - Maintenance, Inspection, and Testing. The
power factor of a stored bushing should be
checked before putting it in service.
checked periodically for oil level, mechanical
damage, and power factor as described in section
IV - Maintenance, Inspection, and Testing. The
power factor of a stored bushing should be
checked before putting it in service.
7 (FIST 3-2 11/91)