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May 21, 2021
As an important structure of medium voltage power cable, metal shielding layer will pass capacitive current under normal operation of the cable, and act as the path of short-circuit current in case of short circuit; At the same time, the electromagnetic field generated when the cable is electrified is shielded in the insulated core to reduce the electromagnetic interference to the outside world.
The copper strip shielding is composed of a layer of overlapped soft copper strip, and the double-layer copper strip can also be used for gap wrapping. The nominal thickness of copper strip for single core cable shielding is not less than 0.12mm. The copper wire shield is composed of loosely wound soft copper wire, and its surface is tightly tied with reverse wound copper wire or copper tape. The average gap between adjacent copper wires shall be no more than 4mm.
The shielding method of copper wire and copper strip winding can improve the disadvantages of shielding method of copper strip winding from the structure. It has neither oxide layer produced by copper strip overlapping, nor strong bending and hot and cold deformation, and the copper strip winding is not easy to arch and embed into the insulation shielding layer.
The cross-section of the metal shield directly affects the ability of the cable to withstand the short-circuit current in case of fault. If the cross-section is too small, the short-circuit current will overheat or burn out and damage the insulation. Therefore, it is necessary to determine the cross section of metal shield according to the fault current capacity.
In 10kV and below cable, when conductor section is more than 500, try to use copper wire shielding! If you insist on using copper tape shielding, you need to thicken the thickness of copper tape! According to the conditions of cable laying, if it needs to carry a large short-circuit current, it is recommended to use copper wire shielding. Therefore, the difference between copper tape shielding and copper wire shielding is the ability to carry short-circuit current. Copper wire is slightly larger (also depends on the effect of copper wire). Copper tape is homogenizing magnetic field and shielding.