In the cable power supply system, the grounding capacitor current is large. When the current is greater than the specified value, arc grounding overvoltage will occur. The purpose of neutral point resistance grounding is to inject resistive current into the fault point, make the grounding fault current resistive-capacitive, reduce the phase difference with voltage, reduce the reignition rate after zero-crossing arc extinguishing of fault point current, limit overvoltage to less than 2.6 times of phase voltage, improve the sensitivity of relay protection tripping, and effectively protect the normal operation of the system.