Coal mine power supply system is generally ground substation, 10KV or 6KV power supply through the underground central substation, mining area substation until the power distribution point of the work surface, basically belongs to the vertical mode of four power supply system. The development of electrical equipment in coal mine is developing along with the change of power supply voltage level. Power supply voltage generally adopt 1140V voltage level of 380V and 660V, using comprehensive mechanized working face, using the 3300V voltage is, manual electric tools (coal drill) and underground lighting are specified with the 127V voltage level.