I. Types of Bushings
High-voltage bushings for use on
transformers and breakers are made in
several principal types, as follows:
transformers and breakers are made in
several principal types, as follows:
A. Composite Bushing.- A bushing
in which insulation consists of two or
more coaxial layers of different
insulating materials.
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 used)
and the inside surface of a protective
weather casing (usually porcelain) is
filled with a compound having
insulating properties.
bushing in which the space between
the major insulation (or conductor
where no major insulation is used)
and the inside surface of a protective
weather casing (usually porcelain) is
filled with a compound having
insulating properties.
C. Condenser 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. Condenser bushings may be
one of several types:
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. Condenser bushings may be
one of several 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. These are usually
rated 25 kV and below.
Consists of porcelain tube with no
filler in the space between the shell
and conductor. These 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 used) and the
inside surface of a protective weather
casing (usually porcelain) is filled with
insulating oil.
which the space between the major
insulation (or the conductor where no
major insulation is used) and the
inside surface of a protective weather
casing (usually porcelain) is filled with
insulating oil.
F. Oil Immersed Bushing.- A
bushing composed of a system of
major insulations totally immersed in
a bath of insulating oil.
bushing composed of a system of
major insulations totally immersed in
a bath of insulating oil.
G. Oil-Impregnated Paper-
Insulated Bushing.- A bushing in
which the internal structure is made
of cellulose material impregnated
with oil.
Insulated Bushing.- A bushing in
which the internal structure is made
of cellulose material impregnated
with oil.
H. Resin-Bonded, Paper-
Insulated Bushing.- A bushing in
which the major insulation is
provided by cellulose material
bonded with resin.
Insulated Bushing.- A bushing in
which the major insulation is
provided by cellulose material
bonded with resin.
I. Solid (Ceramic) Bushing.- A
bushing in which the major
insulation Is provided by a ceramic
or analogous material.
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 caused by moisture entering the
bushing through leaky gaskets or other
openings. Close periodic inspection to find
leaks and make repairs as needed will
prevent most outages due to bush-lng
failures. Such an external inspection re-
quires little time and expense and will be
well worth the effort. High-voltage bushings,
if allowed to deteriorate, may explode with
considerable violence and cause extensive
damages to adjacent equipment.
percent of all preventable bushing failures
are caused by moisture entering the
bushing through leaky gaskets or other
openings. Close periodic inspection to find
leaks and make repairs as needed will
prevent most outages due to bush-lng
failures. Such an external inspection re-
quires little time and expense and will be
well worth the effort. High-voltage bushings,
if allowed to deteriorate, may explode with
considerable violence and cause extensive
damages to adjacent equipment.
Flashovers may be caused by deposits of
dirt on the bushings, particularly in areas
where there are contaminants such as salts
or conducting dusts in the air. These
deposits should be removed by periodic
cleaning.
dirt on the bushings, particularly in areas
where there are contaminants such as salts
or conducting dusts in the air. These
deposits should be removed by periodic
cleaning.
troubles and the inspection methods used
to detect them.
to detect them.
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
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)