A
bushing is an
electrical engineeringElectrical engineering, sometimes referred to as electrical and electronic engineering, is a field of engineering that deals with the study and application of electricity, electronics and electromagnetism. The field first became an identifiable occupation in the late nineteenth century after...
component that
insulatesAn insulator, also called a dielectric, is a material that resists the flow of electric current. An insulating material has atoms with tightly bonded valence electrons. These materials are used in parts of electrical equipment, also called insulators or insulation, intended to support or separate...
a
high voltageThe term high voltage characterizes electrical circuits, in which the voltage used is the cause of particular safety concerns and insulation requirements...
conductor passing through a metal enclosure. Bushings appear on
switchgearThe term switchgear, used in association with the electric power system, or grid, refers to the combination of electrical disconnects, fuses and/or circuit breakers used to isolate electrical equipment. Switchgear is used both to de-energize equipment to allow work to be done and to clear faults...
,
transformerA transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core, and thus a varying magnetic field...
s,
circuit breakerA circuit breaker is an automatically-operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow...
s and other high voltage equipment.
The bushing is a hollow
insulatorAn insulator, also called a dielectric, is a material that resists the flow of electric current. An insulating material has atoms with tightly bonded valence electrons. These materials are used in parts of electrical equipment, also called insulators or insulation, intended to support or separate...
, allowing a conductor to pass along its centre and connect at both ends to other equipment.
Bushings are often made of wet-process fired
porcelainPorcelain is a ceramic material made by heating raw materials, generally including clay in the form of kaolin, in a kiln to temperatures between and...
, and may be coated with a semi-conducting glaze to assist in equalizing the electrical stress along the length of the bushing.
The inside of the bushing may contain paper insulation and the bushing is often filled with oil to provide additional insulation.
A
bushing is an
electrical engineeringElectrical engineering, sometimes referred to as electrical and electronic engineering, is a field of engineering that deals with the study and application of electricity, electronics and electromagnetism. The field first became an identifiable occupation in the late nineteenth century after...
component that
insulatesAn insulator, also called a dielectric, is a material that resists the flow of electric current. An insulating material has atoms with tightly bonded valence electrons. These materials are used in parts of electrical equipment, also called insulators or insulation, intended to support or separate...
a
high voltageThe term high voltage characterizes electrical circuits, in which the voltage used is the cause of particular safety concerns and insulation requirements...
conductor passing through a metal enclosure. Bushings appear on
switchgearThe term switchgear, used in association with the electric power system, or grid, refers to the combination of electrical disconnects, fuses and/or circuit breakers used to isolate electrical equipment. Switchgear is used both to de-energize equipment to allow work to be done and to clear faults...
,
transformerA transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core, and thus a varying magnetic field...
s,
circuit breakerA circuit breaker is an automatically-operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow...
s and other high voltage equipment.
Description
The bushing is a hollow
insulatorAn insulator, also called a dielectric, is a material that resists the flow of electric current. An insulating material has atoms with tightly bonded valence electrons. These materials are used in parts of electrical equipment, also called insulators or insulation, intended to support or separate...
, allowing a conductor to pass along its centre and connect at both ends to other equipment.
Bushings are often made of wet-process fired
porcelainPorcelain is a ceramic material made by heating raw materials, generally including clay in the form of kaolin, in a kiln to temperatures between and...
, and may be coated with a semi-conducting glaze to assist in equalizing the electrical stress along the length of the bushing.
The inside of the bushing may contain paper insulation and the bushing is often filled with oil to provide additional insulation. Bushings for medium-voltage and
low-voltageLow voltage is an electrical engineering term that broadly identifies safety considerations of an electricity supply system based on the voltage used. While different definitions exist for the exact voltage range covered by "low voltage", the most commonly used ones include "mains voltage"...
apparatus may be made of resins reinforced with paper. The use of
polymerA polymer is a large molecule composed of repeating structural units typically connected by covalent chemical bonds. While polymer in popular usage suggests plastic, the term actually refers to a large class of natural and synthetic materials with a variety of properties.Due to the extraordinary...
bushings for high voltage applications is becoming more common. The largest high-voltage bushings made are usually associated with high-voltage direct-current converters.
Capacitor types
Some of the higher voltage types (layers of conductive paper, film, ink or aluminum foil are used with an insulating medium) are called
capacitorA capacitor or condenser is a passive electronic component consisting of a pair of conductors separated by a dielectric. When a voltage potential difference exists between the conductors, an electric field is present in the dielectric. This field stores energy and produces a mechanical force...
bushings because they form a low value capacitor between the conductor and the wall. This is done to reduce the electrical field stress that would otherwise occur and cause
breakdownThe term electrical breakdown has several similar but distinctly different meanings. The term can apply to the failure of an electric circuit....
.
Bushing failure
Bushings sometimes fail due to
partial dischargeIn electrical engineering, a partial discharge is a localised dielectric breakdown of a small portion of a solid or liquid electrical insulation system under high voltage stress...
degradation in the insulation. There is at present great interest in the electricity supply industry in monitoring the condition of high voltage bushings.
See also
In
mechanical engineeringMechanical Engineering is an engineering discipline that was developed from the application of principles from physics and materials science. Mechanical engineering involves the analysis, design, manufacturing, and maintenance of various systems...
, a
bushingA bushing is a type of bearing. It is a cylindrical lining designed to reduce friction and wear inside a hole, or constrict and restrain motion of mechanical parts.- Threaded Insert :...
or plain bearing refers to a part which allows a rotating component to pass through a stationary one, the bushing carrying the load.