The long-term allowable cable current rate refers to the current value when the current in the cable passes through, and the temperature of the cable conductor reaches the long-term allowable operating temperature after the thermal stability is reached.The carrying capacity depends on the maximum allowable working temperature of the product, and has a great relationship with the working system of electrification (such as long-term continuous load, variable load, intermittent load operation, etc.) as well as the laying mode and environmental conditions of electric wires and cables.The carrying current usually refers to the allowable operating current in the case of long-term continuous load operation, and is converted in other cases accordingly.
Electric wires and cables used for power and lighting lines and used for special occasions, such as high voltage ignition wires for vehicles and compensation wires for instrument measuring systems, are not required for carrying capacity.
It is correct that the cable manufacturer only provides the cable section data, not the cable rated current data.Since the rated current of the cable is related to the environment, the working continuity rate of the load, the allowable working temperature of the cable insulation material, the allowable pressure drop of the cable and other parameters, it should be selected by the electrical designer of the purchaser after thorough consideration.
The economic section of the cable is still misunderstood.Some designers and owners think that the minimum section of the cable is the economic section if the temperature rise does not exceed the standard requirements. This is a wrong view, because he ignores the economic losses caused by the energy consumption of the cable itself.Under the same load, the larger the cable section, that is, the smaller the current density of the cable, the smaller the energy consumption of the cable.
The temperature rise of the cable is related to the current density. The higher the current density is, the higher the temperature rise will be.The life of the insulating material is related to the working temperature of the insulating material.The higher the working temperature of insulating material is, the shorter its life is.
The economic section of the cable is a comprehensive parameter, which involves the initial investment cost of the cable, the energy consumption cost within the service life of the cable, the service life of the cable, etc.It is generally accepted in China that the economic cross section of the cable is twice as large as that for temperature rise only.
Post time: Nov-23-2020