View source for Busbar

{{Short description|Strip inside switchgear for local high current distribution}}
{{Hatnote|For Electrical busbar system, see  [[Electrical busbar system]].}}
{{More footnotes|date=August 2014}}
{{Power engineering}}
[[File:Busbar in an LT panel.png|thumb|Copper busbar in a panel]]
[[File:Busbars.jpg|thumb|upright|1500 [[ampere]] [[copper]] busbars within a power distribution rack for a large building]]
In  [[electric power distribution]], a '''busbar'''  (also '''bus bar''') is a metallic strip or bar, typically housed inside [[switchgear]], [[Distribution board|panel boards]], and [[Bus duct|busway enclosures]] for local high current power distribution. They are also used to connect high voltage equipment at electrical switchyards, and low-voltage equipment in [[Electric battery|battery 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==
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 {{convert|10|mm2}}, but [[electrical substation]]s may use metal tubes {{convert|50|mm}} in diameter or more as busbars. [[Aluminium smelter]]s use very large busbars to carry tens of thousands of [[ampere]]s to the [[electrochemical cell]]s that [[Hall–Héroult process|produce aluminium]] from molten [[salts]].
Busbars are produced in a variety of shapes, including flat strips, solid bars and rods, and are typically composed of [[copper]], [[brass]] or [[aluminium]] as solid or hollow tubes.<ref>{{cite web |url=http://copperalliance.org.uk/docs/librariesprovider5/pub-22-copper-for-busbars/copper-for-busbars-all-sections.pdf?sfvrsn=2 |format=PDF |title=Copper for Busbars: Guidance for Design and Installation |website=CopperAlliance.org.uk |archive-date=19 February 2018 |archive-url=https://web.archive.org/web/20180219115627/http://copperalliance.org.uk/docs/librariesprovider5/pub-22-copper-for-busbars/copper-for-busbars-all-sections.pdf?sfvrsn=2 |url-status=live |access-date=30 October 2017 }}</ref> Some of these shapes allow [[heat]] to dissipate more efficiently due to their high [[surface area]] to [[Cross section (geometry)|cross-sectional]] area ratio. The [[skin effect]] makes [[Utility frequency|50–60 Hz]] [[alternating current|AC]] busbars more than about {{convert|8|mm|in}} thickness inefficient, so hollow or flat shapes are prevalent in higher-current applications. A hollow section also has higher [[stiffness]] than a solid rod of equivalent current-carrying capacity, which allows a greater span between busbar supports in outdoor [[Electrical substation|electrical switchyards]].
A busbar must be sufficiently rigid to support its own weight, and forces imposed by mechanical [[vibration]] and possibly [[earthquake]]s, as well as accumulated [[Precipitation types|precipitation]] in outdoor exposures. In addition, [[thermal expansion]] from temperature changes induced by [[ohmic heating]] and ambient temperature variations, and [[magnetic force]]s induced 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.<ref>{{cite web|url=http://www.starlinepower.com/busbar-faq/|title=What is a Busbar & Other FAQs on Electrical Copper Busbars|website=Starlinepower.com|access-date=30 October 2017|archive-url=https://web.archive.org/web/20171030185939/http://www.starlinepower.com/busbar-faq/|archive-date=30 October 2017|url-status=dead}}</ref> Insulated bus bars are used in busways listed to UL 857 standards.<ref>{{cite web |url=https://busstrut.com/busstrut-one-system/power-connections/ |title=Power Drops / Distribution |website=busstrut.com |access-date=13 January 2024 }}</ref> Power [[Ground and neutral|neutral]] busbars may also be insulated because it is not guaranteed that the potential between power neutral and safety grounding is always zero. [[Ground and neutral|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, or [[isolated-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 are [[Plating#Silver plating|silver-plated]] to reduce [[contact resistance]].  At [[extra high voltage]]s (more than 300&nbsp;kV) in outdoor buses, [[corona discharge]] around the connections becomes a source of [[radio-frequency interference]] and [[power loss]], so special connection fittings designed for these voltages are used.
<gallery mode="packed" caption="110 kV busbars in [[electrical substation]]s">
UW_Ebingen_Sammelschienen.jpg|flexible busbar<ref>{{Cite web|url=http://www.electropedia.org/iev/iev.nsf/display?openform&ievref=605-02-22|title=IEC 60050 – International Electrotechnical Vocabulary – Details for IEV number 605-02-22: "flexible busbar"|access-date=2019-01-27|archive-date=2019-01-28|archive-url=https://web.archive.org/web/20190128030458/http://www.electropedia.org/iev/iev.nsf/display?openform&ievref=605-02-22|url-status=live}}</ref>
Kändelweg Sammelschienen.jpg|rigid busbar<ref>{{Cite web|url=http://www.electropedia.org/iev/iev.nsf/display?openform&ievref=605-02-21|title=IEC 60050 – International Electrotechnical Vocabulary – Details for IEV number 605-02-21: "rigid busbar"|access-date=2019-01-27|archive-date=2019-01-28|archive-url=https://web.archive.org/web/20190128030457/http://www.electropedia.org/iev/iev.nsf/display?openform&ievref=605-02-21|url-status=live}}</ref>
</gallery>
==See also==
* {{Annotated link|Bus (computing)}}
* {{Annotated link|Bus duct}}
* {{Annotated link|Electrical busbar system}}
* {{Annotated link|Jumper (computing)}}
* {{Annotated link|Wire bridge}}
==References==
{{Reflist}}
==Further reading==
* {{cite book |last=Elmore |first=Walter A. |date=1994 |title=Protective Relaying Theory and Applications |publisher=Marcel Dekker |isbn=978-0-8247-9152-0 }}
* {{cite web |last=Paschal |first=John |url=http://ecmweb.com/mag/electric_ensuring_good_bus/ |title=Ensuring a Good Bus Duct Installation |work=Electrical Construction & Maintenance |date=2000-10-01 |access-date=2009-04-06 }}
==External links==
* {{Commons category-inline|Busbars}}
{{Electricity delivery}}
[[Category:Electric power systems components]]