The cross-sectional size of the busbar determines the maximum amount of current that can be safely carried. Busbars can have a cross-sectional area of as little as 10 mm2, but electrical substations may use metal tubes 50 mm in diameter (20 cm2) or more as busbars. An aluminium smelter will have very large busbars used to carry tens of thousands of amperes to the electrochemical cells that produce aluminium from molten salts.
Busbars are typically contained inside switchgear, panel boards, or busway enclosures. Distribution boards split the electrical supply into separate circuits at one location. Busways, or bus ducts, are long busbars with a protective cover. Rather than branching from the main supply at one location, they allow new circuits to branch off anywhere along the route of the busway.
A busbar may either be supported on insulators, or else insulation may completely surround it. Busbars are protected from accidental contact either by a metal earthed enclosure or by elevation out of normal reach. Power Neutral busbars may also be insulated. Earthing (safety grounding) busbars are typically bare and bolted directly onto any metal chassis of their enclosure. Busbars may be enclosed in a metal housing, in the form of bus duct or busway, segregated-phase bus, or isolated-phase bus.
The strain bus-bar is a flexible, stranded conductor which is strung between substation metal structures and held by suspension-type insulators.
(2) Insulated-phase bus-bars, used at medium voltage
The insulated-phase bus-bar is a rigid bar supported by insulators and covered by a grounded metal shield. The main advantage of this system is the elimination of short circuits between adjacent phases.
(3) Sulfur hexafluoride (SF6)-insulated bus-bars, used in medium- and high-voltage systems
The sulfur hexafluoride-insulated bus-bar is a rigid aluminum tube, supported by insulators and installed in a larger metal tube, which is filled with high-pressure sulfur hexafluoride gas.
Advantages of Busbar Chambers
Busbars (usually 99% pure copper) are mainly used inside Main Switchboards. A Main Switchboard is an electrical distribution board that distributes electricity to large buildings or establishments. Busbar configurations can also be found in High Voltage switchyards/sub-stations.
As mentioned by others, they are used to carry high current. They have some advantages over cable;
1] They are rigid & can therefore tolerate the huge magnetic forces under "fault" conditions (provided they are supported correctly).
2] They are usually uninsulated or "tinned". In either case, they radiate heat better than insulated cables. As a result, a 1000 amp busbar is somewhat smaller than a cable of the same current rating.
Disadvantages of Busbar Chambers
1] Busbar is more difficult to install than cable because busbars require bending & cutting, which can only be done by large equipment. They must be bolted together using special bolts & then tensioned correctly.
2] Because they are usually uninsulated, there is an increased "arcing" hazard if they are not spaced correctly.
3] A "specialist" electrician is required to manufacture & install busbar into switchboard apparatus.
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