How to choose different cross-sections of dense busbars? The selection and application of dense busbars should consider different types and materials of busways under different environmental conditions. In addition, for various bus ducts, the selection of bus duct sections should usually be based on the long-term operating current. And verify the short-term thermal stability of the bus duct under high short-circuit current conditions. Due to factors such as the resistance of multiple conductors in close proximity and the metering effect of alternating current, the bus duct will generate heat when current passes through. The allowable heating temperature for copper and aluminum busbars during long-term operation is 70 ℃, but when the contact surface is reliably covered with tin (such as ultrasonic tin plating), the allowable temperature can be increased to 85 ℃. Due to the limitation of the allowable temperature for continuous heating, busbars of different materials and cross-sections are given corresponding long-term allowable current values. When selecting a busbar section, the actual long-term operating current of the busbar (considering over half an hour) should be subtracted to be less than the long-term allowable current value of the selected section busbar slot

In situations where the average annual load is high and the conductors and bus ducts are the main body (such as outdoor distribution equipment bus ducts), the bus ducts are usually selected using the economic current density method. Economic current density refers to the current flowing through a unit cross-sectional area of a bus duct, taking into account the low losses, annual maintenance, and depreciation costs of the bus duct and associated equipment. Divide the economic current density by the long-term operating current (excluding overload) to obtain the busbar cross-section. The cross-sectional area of the bus duct selected by the economic current density method is generally larger than that selected by the long-term operating current.

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