Abstract: For faults in leakage protection of smart low-voltage feed switch of Nantun Coal Mine, the paper analyzed leakage protection principle and causes of the faults, and proposed reformation schemes: increase zero sequence current by additional capacitance at the master switch, so that integrated protector can be used for acquisition and judgment, and sub switch of the leakage branch can operate reliably; connect a circuit breaker auxiliary contact normally closed in series in leakage detection circuit of sub switch, so that detection circuit based on additional DC power principle can be cut off completely after closing of the sub switch to eliminate interference to leakage detection of master switch. Field application results show that the improved leakage protection of the low-voltage power supply system operates normally, leakage action time is shortened from 2 s to less than 250 ms, and the leakage protection of sub switch acts sensitively and reliably.