1. The working temperature of insulation materials is higher

The current carrying capacity of the bus duct is related to the higher working temperature of the insulation material. The temperature rise caused by the conductor load during normal continuous operation should not exceed the specified temperature. The higher operating temperature of bus ducts is different from that of wires. It refers to the temperature of the sheath. The sheath mainly serves to protect the insulation. Therefore, the working temperature of cable insulation sheath material is higher than that of wire insulation material.

The temperature rise of the busbar is not related to the voltage applied to the busbar, but only to the current flowing through the busbar. Under the same cross-sectional structure, the higher the current density passing through, the higher the temperature rise of the bus duct.

2. Environmental temperature correction coefficient

Obviously, the higher the temperature, the smaller the allowable current carrying capacity of the bus duct. Assuming an air ambient temperature of 30 ° C based on the current carrying capacity provided in various technical manuals; For bus ducts directly buried underground or laid in urban underground pipelines, assuming a temperature of 20 ° C. If the environment is different, multiply by a correction factor. The correction factor is related to the temperature of the environment and the high working temperature of the insulation material.

3. Correction factor for bus duct laying method

There are many ways to lay bus ducts. Taking bridges as an example, they can be laid in perforated trays, perforated trays, brackets, and ladders, with or without covers. Different laying methods have different correction factors.

In engineering, it is often found that due to the limitation of cable cross-section, in order to increase capacity. Cables can be used in a dual or even triple manner. This method is not advisable because when multiple cables are connected in parallel, the contact resistance at the joint is different, and this contact resistance is often equal to the resistance of the cable itself. As a result, the current distribution of multiple parallel cables will be unbalanced. Therefore, bus ducts are used for large capacity distribution main lines. Although the price of using bus ducts is higher than that of cables, from the perspective of product cost-effectiveness, bus ducts are increasingly favored by Chinese designers and owners.