FACILITIES INSTRUCTIONS, STANDARDS,
AND TECHNIQUES
Volume 3-2
TESTING AND MAINTENANCE OF HIGH-VOLTAGE BUSHINGS FACILITIES ENGINEERING BRANCH DENVER OFFICE
DENVER, COLORADO
Internet Version of This Manual Created
August 2000
The Appearance of the Internet Version of This Manual
May Differ From the Original, but the Contents Do Not
UNITED STATES DEPARTMENT OF THE INTERIOR
假期安排去腾冲旅游攻略BUREAU OF RECLAMATION
NOVEMBER 1991
CONTENTS
Section Page I Types of Bushings (1)
II Bushing Troubles (1)
III Safety (1)
IV Maintenance, Inspection, and Testing (3)
V Storage of Bushings (7)
Bibliography (8)
TABLES
Table Page
1 Bushing Troubles (2)
2 Manufacturer's Power-Factor Limits for Bushings (6)
i (FIST 3-2 11/91)
I. Types of Bushings
High-voltage bushings for u on transformers and breakers are made in veral principal types, as follows:
A. Composite Bushing.- A bushing
in which insulation consists of two or
more coaxial layers of different
insulating materials.
B. Compound-Filled Bushing.-A
bushing in which the space between
the major insulation (or conductor
where no major insulation is ud)
and the inside surface of a protective
weather casing (usually porcelain) is
filled with a compound having
insulating properties.
C. Condenr Bushing.- A bushing
in which cylindrical conducting layers
are arranged coaxially with the
conductor within the insulating
material. The length and diameter of
the cylinders are designed to control
the distribution of the electric field in
and over the outer surface of the
bushing. Condenr bushings may be
one of veral types:
1. Resin-bonded paper insulation;
2. Oil-impregnated paper insulation; or
3. Other.
D. Dry or Unfilled Type Bushing.-
Consists of porcelain tube with no
filler in the space between the shell
and conductor. The are usually
rated 25 kV and below.
E. Oil-Filled Bushing.- A bushing in
which the space between the major
insulation (or the conductor where no
major insulation is ud) and the
inside surface of a protective weather
casing (usually porcelain) is filled with
insulating oil.
F. Oil Immerd Bushing.- A
bushing compod of a system of
major insulations totally immerd in
a bath of insulating oil.
G. Oil-Impregnated Paper-
Insulated Bushing.- A bushing in
which the internal structure is made
of cellulo material impregnated
with oil.
H. Resin-Bonded, Paper-
Insulated Bushing.- A bushing in
which the major insulation is
provided by cellulo material
bonded with resin.
孰重孰轻I. Solid (Ceramic) Bushing.- A
bushing in which the major
insulation Is provided by a ceramic
or analogous material.
II. Bushing Troubles
Operating records show that about 90 percent of all preventable bushing failures are caud by moisture entering the bushing through leaky gaskets or other openings. Clo periodic inspection to find leaks and make repairs as needed will prevent most outages due to bush-lng failures. Such an external inspection requires little time and expen and will be well worth the effort. High-voltage bushings, if allowed to deteriorate, may explode with considerable violence and cau extensive damages to adjacent equipment. Flashovers may be caud by deposits of dirt on the bushings, particularly in areas where there are contaminants such as salts or conducting dusts in the air. The deposits should be removed by periodic cleaning.
Table 1 lists the common caus of bushing troubles and the inspection methods ud to detect the
m.
III. Safety
At all times, safety is the most important consideration. All testing work on bushings shall be performed in accordance with the ROMSS (Reclamation Operation and Maintenance Safety Standards) which establish safety standards and safe work practices for operations and activities performed by the Bureau. The
1 (FIST 3-
2 11/91)
Table 1. - Bushing troubles Trouble Possible Methods of
results detection
Cracked porcelain Moisture enters. Visual inspection.
Oil and/or gas Power factor test.
leaks. Hot collar test
Filler leaks out.
Deterioration of Moisture enters, Visual inspection. cemented joints Oil and/or gas Power factor test.
leaks. Hot collar test.
Filler leaks out.
Gasket leaks Moisture enters. Visual inspection.
吴的组词Oil and/or gas Power factor test.
leaks. Hot collar test.
Filler leaks out. Hot-wire test for
moisture.
Insulation resis
tance.
Moisture in Moisture enters. Power factor test, insulation Hot collar test.
Solder al leak Moisture enters. Visual inspection.
Filler leaks out. Power factor test.
Hot collar test.
Hot-wire test for
moisture.
Leak detector.
Broken connection Sparking in appa-Power factor test. between ground ratus tank or
sleeve and flange within bushing.
Discolored oil.
Voids in compound Internal corona. Hot collar test.
Power factor tip-
up test.
Oil migration Filler contamina-Visual inspection.初三物理公式
tion. Power factor test.
Hot collar test.
No oil Oil leaks out. Visual inspection,
Moisture enters. Power factor test.
Hot collar test.
Displaced grading Internal sparking Hot collar test.
shield discolors oil.
Electrical fiashover Cracked or bro-Visual inspection.
ken porcelain. Hot collar test.
Complete failure.
Lightning Cracked or bro-Visual inspection.
ken porcelain. Test lightning
Complete failure. arrestors. Table 1. - Bushing troubles - Continued
Trouble Possible
results
Methods of
detection
Corona Internal break
down.
Radio interfer
ence.
Treeing along sur
face of paper or
internal sur
faces.
Power factor test
Hot collar test.
Hot-wire test.
RRIV
Short-circuited
condenr ctions
Incread capaci
tance.
Reduced voltage
at capacitance
tap terminal.
Adds internal
stress to insula
tion.
Power factor test.
Voltage test at
capacitance tap.
Capacitance test.
Darkened oil Radio interfer
ence,
Poor test results.
Power factor test.
Hot collar test.
following are minimum suggestions for safety
and are not intended to superde safety practices established by individual regions or the ROMSS.
A. Handling. -When handling bushings,
care must be taken to be sure that rigging is
applied properly to prevent damage to the
bushing and/or to adjacent equipment and
personnel.
Cracked or chipped porcelain produce sharp
edges which can result in vere cuts on the
hands and arms of personnel working around
them.
B. Static Charges. -Static charges induced
by test potentials provide a source for rious
accidents through falls caud by reflex action, High- static voltages may be encountered at
the bushings installed in apparatus during cold weather and oil-handling operations. Protective or safety grounds should be ud to bleed off static charges. High-static charges may also be encountered at the bushing capacitance taps if
(FIST 3-2 11/91) 2
the covers are removed. The also
should be grounded before being handled.
Induced voltages from nearby energized
lines can cau rious accidents if they
are not handled properly. Employees
should be constantly reminded of the
possibility of induced charges and the
dangers Involved.
Induced voltages of steady-state nature
are often encountered when the deenergized circuit cloly parallels another energized circuit. In such instances, protective grounds should be
applied to the circuit at the bushings to be
inspected. If electrical tests are to be
conducted, the grounded leads may be
removed which would prevent such tests.
Refer to FIST Volume 1-1.
C. Field Testing.-Field testing generally
requires work in the proximity of energized equipment. A hazard analysis
should be performed and a short safety
meeting on the site should be conducted
prior to beginning field tests on bushings.
Adjacent high-voltage equipment which
may be hazardous to workmen shall be
marked off with visible warning devices,
such as tape, rope, or portable fence
ctions. Signs reading "DANGER - DO
NOT PASS THIS BARRIER, -- DANGER
-HIGH VOLTAGE," or similar notice
shall be placed along the barriers facing
the working area.
IV. Maintenance, Inspection,
and Testing
A. General.-All high-voltage bushings
should be inspected periodically to intervals of not over 3-5 years. The
inspections should include power-factor
tests for all bushings rated above 115 kV.
Lower voltage bushings should also be
tested if there is reason to suspect they
may be deteriorated. Bushings showing
signs of deterioration should be tested at
intervals of 6 months to 1 year and removed from rvice if the tests show a dangerous condition.
1. Terminal caps end connectors.
Check for tightness to avoid poor contact
and resultant heating.
2. Capacitance taps and power-factor
test electrodes.-Check to determine
proper grounding for bushings with a
grounded capacitance tap and for power-
factor test electrodes. Examine for proper
gasketing to prevent entrance of mois
ture.
3. Cement.-Check for crumbling or
chipped and repair as required.
4. Gaskets.-Check gaskets for
deterioration, looness, and leaking.
Loo gaskets should be replaced or
painted with General Electric lacquer or
other suitable oil-proof aler, and
tightened. Finding a loo gasket or al
may mean that moisture has entered the
bushing, and checks should be made to
determine if moisture is prent. The
bushing should be dried out if necessary.
5. Metal pads.-Check and paint as nec
essary. Examine structural parts, such as
clamping rings and washers, for cracks or
breaks.
6. Solder als.-Check for cracks and
leaks and repair as necessary.
B. Visual Inspection Annually with Binoculars.-The visual inspection should include the following items:
1. Porcelain.- Check for chips, cracks,
and contamination. Minor chips may be
painted with an insulating varnish to ob
tain a glossy finish which will shed dirt
and moisture. Superficial cracks that do
not affect the mechanical or electrical
strength of the bushing may be aled一见倾心的意思
with insulating varnish or epoxy. Bush恐龙的特点
ings with major chips or cracks which
appreciably decrea the creepage dis
tance should be replaced. The surface of
the porcelain should be cleaned as
3 (FIST 3-2 11/91)
needed to remove dirt, oil, and other deposits that may reduce the flashover value.
2. Oil level.-Check the oil level on
bushings equipped with sight gauges or
other types of oil-level indicators and
add oil as necessary. Low-oil levels with
no sign of an external leak may Indicate
a leak within the bushings which may
require replacement of the bushing as
field corrections would be difficult to
accomplish. The oil level of bushings
without oil-level indicators is not
normally checked unless there is
evidence of leakage.
C. Maintenance Tests.-Common maintenance tests are power factor, RIV (radio-in-fluence-voltage),
dc insulation resistance, and testing oil or compound for moisture. Descriptions of the various tests follow:
1. Power-factor Doble Tests.- The
power-factor test is the most effective
known field test procedure for the
early detection of bushing
contamination and deterioration. This
test also provides measurement of ac
test current which is directly
proportional to bushing capacitance.
Bushings may be tested by one or
more of four methods depending
upon the type of bushing and the
power-factor test t available. For
more complete detailed instructions
on the method of test and test
procedure, plea e the
appropriate power-factor test t
instruction book. The four test
methods are as follows:
a. The GST (grounded specimen
test).-This test measures the夸女人的话
insulating qualities of the insulation
between the current carrying or
center conductor and the mounting
flange of a bushing. The application
of such a test is necessarily limited to
bushings out of the apparatus such
as spare bushings, or bushings which (FIST 3-2 11/91) 4 have been isolated from connected windings and interrupters. The test is performed by energizing the bushing conductor and grounding the flange. Large variations in temperature have a significant effect on power-factor readings on certain types of bushings. For comparative purpos, readings should be taken at the same temperature, or corrections should be applied before comparing readings taken at different temperatures.
b. The hot-guard test.-This test measures the insulation between the cur-rent-carrying or center conductor and the mounting flange of a bushing. The test was designed specifically for "draw-lead" type bushings but is applicable to any bushing in apparatus which can be isolated from connecting w
indings and bus, but not sufficiently to withstand test potential. Both the bushing and the draw-lead, winding, and bus are energized at the same test potential, but only the current and loss of the bushing are measured.
c. The UST (ungrounded-specimen test).-This test measures the insulation between the current-carrying or center conductor and the capacitance tap, power-factor tap, and/or ungrounded flange of a bushing. This test may be applied to any bushing in or out of apparatus which is either equipped with capacitance or power-factor taps or the flange of which can be isolated from the grounded tank in which the bushing is installe
d. The insulation resistance between the taps or insulated flanges and ground should be 0.5 meg-ohm or better. While in this ca, anything that is attached to the bushing (such as contact asmblies or transformer windings) would also be energized; only the insulation of the bushing between
