Due to electromagnetic induction, the metal shield (or metal sheath) of the long-line high-voltage single-core power cable generates induction voltage, which leads to insulation aging, and at the same time reduces the insulation level, resulting in a decrease in cable life; once the induced voltage exceeds the set breakdown voltage value, The outer sheath is broken down to form a single-core cable multi-point ground fault.

Therefore, the power industry standard DL/T401 《Guidelines for the Selection of High Voltage Power Cables》 stipulates that a cable sheath protector must be used to limit the induced voltage and fault overvoltage on the power metal shield (or metal sheath).