the center conductor and the
ungrounded tap or flange would be
measured. In the case of bushings
equipped with capacitance taps, a
supplementary test should always be
made on the insulation between the
tap and the flange.
ungrounded tap or flange would be
measured. In the case of bushings
equipped with capacitance taps, a
supplementary test should always be
made on the insulation between the
tap and the flange.
d. The hot-collar test.- This test mea-
sures the condition of a specific small
section of bushing insulation between
an area of the upper porcelain
rainshed and the current-carrying or
center conductor. It is performed by
energizing one or more electrodes
(collars) placed around the bushing
porcelain with the bushing center
conductor grounded. This test is used
to supplement the three tests
described above or to test bushings in
apparatus when the above-mentioned
three tests are either inapplicable or
impractical. Hot-collar tests are
effective in locating cracks in
p o r c e l a i n , d e t e r i o r a t i o n o r
contamination of insulation in the
upper section of a bushing, low com-
pound or liquid level, or voids in com-
pound, often before such defects are
noticeable with the tests outlined in
subparagraphs a., b., and c.
sures the condition of a specific small
section of bushing insulation between
an area of the upper porcelain
rainshed and the current-carrying or
center conductor. It is performed by
energizing one or more electrodes
(collars) placed around the bushing
porcelain with the bushing center
conductor grounded. This test is used
to supplement the three tests
described above or to test bushings in
apparatus when the above-mentioned
three tests are either inapplicable or
impractical. Hot-collar tests are
effective in locating cracks in
p o r c e l a i n , d e t e r i o r a t i o n o r
contamination of insulation in the
upper section of a bushing, low com-
pound or liquid level, or voids in com-
pound, often before such defects are
noticeable with the tests outlined in
subparagraphs a., b., and c.
When bushings with capacitance or potential
taps (92 kV and above) are tested by the
ungrounded test specimen method, it is
recommended practice to include a separate
power-factor test on the tap Insulation as well.
The exception to this is General Electric
Company type of bushings built prior to 1932,
which have tap outlets designed to operate at
less than 100 volts. On all other capacitance
or potential taps, tests are performed at some
voltage from 2 to 5 kV. The procedure is to
energize the tap with the bushing center
conductor and flange grounded. The power
factor of a capacitance or potential tap will
generally be of the order of 1.0 percent or
less.
taps (92 kV and above) are tested by the
ungrounded test specimen method, it is
recommended practice to include a separate
power-factor test on the tap Insulation as well.
The exception to this is General Electric
Company type of bushings built prior to 1932,
which have tap outlets designed to operate at
less than 100 volts. On all other capacitance
or potential taps, tests are performed at some
voltage from 2 to 5 kV. The procedure is to
energize the tap with the bushing center
conductor and flange grounded. The power
factor of a capacitance or potential tap will
generally be of the order of 1.0 percent or
less.
PermissibleTest Potentials to be Applied to
Power-Factor Taps
Manufacturer
Bushing type
Test
or class
volts
General Electric
LC, U
2000
Lapp
POC
2000
Ohio Brass
L
250
Ohio Brass
GK, LK
500
Pennsylvania (Federal Pacific)
P
500
Westinghouse
S, OS
500
Routine tap-insulation tests are not normally
recommended for bushings rated 69 kV and
below with power-factor taps. However, a power-
factor test of the tap insulation should be
performed when questionable ungrounded
specimen test results or visual examination cast
suspicion on the condition of the power-factor
tap. The test procedure is as outlined above for
capacitance taps. In such cases, the maximum
permissible test potentials should be limited to
the following table.
recommended for bushings rated 69 kV and
below with power-factor taps. However, a power-
factor test of the tap insulation should be
performed when questionable ungrounded
specimen test results or visual examination cast
suspicion on the condition of the power-factor
tap. The test procedure is as outlined above for
capacitance taps. In such cases, the maximum
permissible test potentials should be limited to
the following table.
The power factor of the power-factor tap
insulation for most of the above- mentioned
bushings will generally be of the order of 1.0
percent or less. The principal exception to this is
the Ohio Brass, type L bushing. The inherent
properties of the fibrous-bakelite material used
for the tap insulator have resulted in power
factors up to 10 percent for apparently
satisfactory taps.
insulation for most of the above- mentioned
bushings will generally be of the order of 1.0
percent or less. The principal exception to this is
the Ohio Brass, type L bushing. The inherent
properties of the fibrous-bakelite material used
for the tap insulator have resulted in power
factors up to 10 percent for apparently
satisfactory taps.
The tabulations of factory power factors and
power-factors limits in
power-factors limits in
by the manufacturers or otherwise listed by
them. Please note, however, that many bushings
have the factory power factor listed on the
nameplate. In such cases, field measurement,
particularly ungrounded specimen tests, should
compare with and the bushings be rated on the
basis of nameplate power factors. In general, any
bushing that exhibits a history of continued
them. Please note, however, that many bushings
have the factory power factor listed on the
nameplate. In such cases, field measurement,
particularly ungrounded specimen tests, should
compare with and the bushings be rated on the
basis of nameplate power factors. In general, any
bushing that exhibits a history of continued
5 (FIST 3-2 11/91)