The invention discloses a selective electric leakage 
protection system for a low-
voltage power grid of an underground 
coal mine, and relates to an electric leakage 
protection system for the underground 
coal mine. The 
system comprises a selective electric leakage protection addition 
DC source method electric leakage detection 
system, a zero-sequence power direction type electric leakage detection 
system, and a selective electric leakage 
protection system. The selective electric leakage protection addition 
DC source method electric leakage detection system is provided with an independent DC power supply between a three-phase 
power grid and the ground. The zero-sequence power direction type electric leakage detection system judges an electric leakage fault 
branch circuit through a zero-sequence 
voltage and a zero-sequence current. The selective electric leakage protection system selects a single-
chip microcomputer in the C8051F040 series, and a CAN2.0B controller is integrated in a 
chip and has a mode of external 
crystal oscillation. A power supply circuit of the system achieves the selective switching-off of an electric leakage circuit through the detection of a zero-sequence current 
signal, and the whole power 
supply network is not 
cut off. The system is reliable in performance, is convenient and effective, is safe and stable, is high in 
cost performance, and achieves the optimization of power supply.