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Selection and Application of Electric Busbars 2012-10-22

A busbar is a strip or a bar of cooper, brass or aluminum used to aggregate, distribute and convey electricity. It is general wire used to convey electric power for hydropower or substation. The electric power input by engine, transformer or rectifier can be conveyed to users or other substations through it. As huge electric power passes through the busbars when they are operating, if they are shorted out, they will bear large heating and electrodynamic effect, reasonable selection of the materials, section forms and sectional areas of the busbars directly affect safety and cost of equipments.
Common busbars include rigid busbars and flexible busbars. The rigid bars are made of cooper or aluminum and their shapes contain rectangle, tank and pipe shape. They are mainly used in indoor distribution equipment with 35KV or below, outdoor distribution equipment with 110KV~220KV usually applies aluminum busbar. On the contrary, the flexible busbars apply to the outdoor distribution equipment with above 35KV. And they are usually made of aluminum wire, cooper wire or steel-cored cooper wire.
According to the materials of busbars, the busbars can be divided into copper bars, aluminum bars, steel busbars and copper clad aluminum busbars. Busbars with different materials apply to different conditions.
Firstly, as copper has high electric conductivity and good wear resistance, the copper busbar is mainly used in corrosion resistant areas such as coastal areas or chemical plants nearby. However, it is very expensive. Secondly, the electric conductivity of aluminum is only less than copper's, as it is light and cheap, the aluminum busbar can be widely used in outdoor and indoor equipments. Thirdly, because of strong mechanical strength and weak conductivity of steel, the steel busbar can only be used in high voltage with small capacity circuit, low voltage with working current with less than 200A and loop of DC circuit and grounding device. In addition, the copper clad aluminum busbar is a kind of composite conductor which applies aluminum as the core and is covered with cooper outside. It integrates advantages of copper busbars and aluminum busbars, that is, it processes conductivity of cooper and low cost of aluminum. So it is widely used in many electric types of equipment.
As conductors are affected by many factors like resistors, busbars will be heated when they pass through the current. The allowing temperature of copper and aluminum busbars is about 70℃. With the limitation of temperature, busbars of different materials and sections give relative longtime current value. Therefore, while elect sections of busbars, the maximum longtime working current should be taken into consideration. Generally, the maximum longtime working current should be less than allowing current of the elected section of the busbar.
Above all, many factors can affect the working performance of busbars. While selecting busbars, one should consider types, materials, sections of busbars and so on.