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Busbar

From Wikipedia, the free encyclopedia
Copper busbar in an LT panel
Copper busbar in an LT Panel
1500amperecopperbusbars within a power distribution rack for a large building

Inelectric power distribution,abusbar(alsobus bar) is a metallic strip or bar, typically housed insideswitchgear,panel boards,andbusway enclosuresfor local high current power distribution. They are also used to connect high voltage equipment at electrical switchyards, and low voltage equipment inbattery banks.They are generally uninsulated, and have sufficient stiffness to be supported in air by insulated pillars. These features allow sufficient cooling of the conductors, and the ability to tap in at various points without creating a new joint.

Design and placement

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The busbar's material composition and cross-sectional size determine the maximum current it can safely carry. Busbars can have a cross-sectional area of as little as 10 square millimetres (0.016 sq in), butelectrical substationsmay use metal tubes 50 millimetres (2.0 in) in diameter (2,000 square millimetres (3.1 sq in)) or more as busbars.Aluminium smeltersuse very large busbars to carry tens of thousands ofamperesto theelectrochemical cellsthatproduce aluminiumfrom moltensalts.

Busbars are produced in a variety of shapes, including flat strips, solid bars and rods, and are typically composed ofcopper,brassoraluminiumas solid or hollow tubes.[1]Some of these shapes allowheatto dissipate more efficiently due to their highsurface areatocross-sectionalarea ratio. Theskin effectmakes50–60 HzACbusbars more than about 8 millimetres (0.31 in) thickness inefficient, so hollow or flat shapes are prevalent in higher-current applications. A hollow section also has higherstiffnessthan a solid rod of equivalent current-carrying capacity, which allows a greater span between busbar supports in outdoorelectrical switchyards.

A busbar must be sufficiently rigid to support its own weight, and forces imposed by mechanicalvibrationand possiblyearthquakes,as well as accumulatedprecipitationin outdoor exposures. In addition,thermal expansionfrom temperature changes induced byohmic heatingand ambient temperature variations, andmagnetic forcesinduced by large currents, must be considered. To address these concerns, flexible bus bars, typically a sandwich of thin conductor layers, were developed. They require a structural frame or cabinet for their installation.

Distribution boards split the electrical supply into separate circuits at one location. Busways, or bus ducts, are long busbars with protective covers. Rather than branching from the main supply at one location, they allow new circuits to branch off anywhere along the busway.

A busbar may be either supported on insulators, or wrapped in insulation. They are protected from accidental contact either by a metal earthed enclosure or by elevation out of normal reach.[2]Insulated bus bars are used in busways listed to UL 857 standards.[3]Powerneutralbusbars may also be insulated because it is not guaranteed that the potential between power neutral and safety grounding is always zero.Earthing(safety grounding) busbars are typically bare and bolted directly onto any metal chassis of their enclosure. They may be enclosed in a metal housing, in the form of a bus duct or busway, segregated-phase bus, orisolated-phase bus.

Busbars may be connected to each other and to electrical apparatus by bolting, clamping or welding. Joints between high-current bus sections often have precisely machined matching surfaces that aresilver-platedto reducecontact resistance.Atextra high voltages(more than 300 kV) in outdoor buses,corona dischargearound the connections becomes a source ofradio-frequency interferenceandpower loss,so special connection fittings designed for these voltages are used.

See also

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References

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  1. ^"Copper for Busbars: Guidance for Design and Installation"(PDF).Copperalliance.org.uk.Archived(PDF)from the original on 19 February 2018.Retrieved30 October2017.
  2. ^"What is a Busbar & Other FAQs on Electrical Copper Busbars".Starlinepower.Archived fromthe originalon 30 October 2017.Retrieved30 October2017.
  3. ^"Power Drops / Distribution".busstrut.Retrieved13 January2024.
  4. ^"IEC 60050 – International Electrotechnical Vocabulary – Details for IEV number 605-02-22:" flexible busbar "".Archivedfrom the original on 2019-01-28.Retrieved2019-01-27.
  5. ^"IEC 60050 – International Electrotechnical Vocabulary – Details for IEV number 605-02-21:" rigid busbar "".Archivedfrom the original on 2019-01-28.Retrieved2019-01-27.

Further reading

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  • Walter A. Elmore (1994).Protective Relaying Theory and Applications.Marcel Dekker Inc.ISBN978-0-8247-9152-0.
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