CYCL asymmetric current source single-phase ground fault the asymmetric current source, close to the vicinity of the substation distribution transformer substation (or line) action, the fault line with the special characteristics of the pulse current signal. 2. Short circuit and ground fault indicator (Short and Grounded Fault Indicator) THFI-II single-phase ground fault occurs, the fault indicator mounted on the fault line detection to asymmetric current source signal flop and flash directions. In order to determine the point where single-phase ground fault outlet, branch and section. Fault indicator can also be indicated by determining the short-circuit current short-circuit fault, this can determine the short-circuit fault point where the outlet, branch and section. Installed in the substation outlet at fault indicator through the optical fiber media converter fault signal is passed to the substation RTU ground fault line selection.