What is the function of the metal tape shield in power cables?
The metal tape shield in power cables is typically made of copper tape wrapped around the outer semi-conductive layer. Its functions are as follows:
1) It strengthens the electric field confinement within the insulation layer, aligning the electric field direction with the insulation radius (i.e., radially). The metal tape is grounded, and the electric field terminates at the tape, with no electric field outside the tape.
2) In a three-phase, four-wire system, it serves as the center conductor to carry unbalanced current.
3) It prevents axial surface discharge. In an environment without a good ground connection, the semi-conductive layer has a certain resistivity, which can cause uneven potential distribution along the cable axis, leading to surface discharge along the cable.
4) Power station protection systems require an outer conductor shield. Wrapped copper tape has excellent lightning protection properties.
5) Under normal circumstances, capacitive current flows through the metal tape, but in the event of a short circuit, the metal tape serves as a return path for the short-circuit fault current.
