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Home>News> Effect of Busbar Arrangements on Rating

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Effect of Busbar Arrangements on Rating 2013-06-27

 The efficiency of all types of heavy current busbars depends upon careful design, the most important factors being: a) The provision of a maximum surface area for the dissipation of heat. b) An arrangement of bars which cause a minimum of interference with the natural movements of air currents. c) An approximately uniform current density in all parts of the conductors. This is normally obtained by having as much copper as possible equidistant from the magnetic centre of the busbar. d) Low skin effect and proximity effect for a.c. busbar systems. To meet these requirements there are many different arrangements of copper busbars using laminations, as well as copper extrusions of various cross-sections.

Laminated copper bars To obtain the best and most efficient rating for rectangular strip copper conductors they should be mounted whenever possible with their major cross-sectional axes vertical so giving maximum cooling surfaces. Laminated copper bars To obtain the best and most efficient rating for rectangular strip copper conductors they should be mounted whenever possible with their major cross-sectional axes vertical so giving maximum cooling surfaces.

Inter-leaving of conductors Where long low-voltage a.c. bars are carrying heavy currents, particularly at a low power factor, inductive volt drop may become a serious problem with laminated bars arranged as in Figure 9a. The voltage drop for any given size of conductor is proportional to the current and the length of the bars, and increases as the separation between conductors of different phases increases. In the case of laminated bars the inductive volt drop can be reduced by splitting up the bars into an equivalent number of smaller circuits in parallel, with the conductors of different phases interleaved as shown in Figure 9b. This reduces the average spacing between conductors of different phases and so reduces the inductive volt drop. Transposition of conductors The unbalanced current distribution in a laminated bar carrying a.c. current due to skin and proximity effects may be counteracted by transposing laminations or groups of laminations at intervals. Tappings and other connections make transposition difficult, but it can be worthwhile where long sections of bars are free from tappings. The arrangement is as shown in Figure 9e.