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In China, current transformers (TAs) are just installed at A-phase and C-phase in most distribution networks with neutral indirectly grounding. It is a very difficult problem to select single-phase grounding line using the currents of A phase and B phase. After analyzing the currents of A-phase and C- phase when B-phase grounding fault occurs, the fault line detection algorithm applying the transient characters of the sum of A-phase mutational current and C-phase mutational current is proposed. For A-phase to ground fault or C-phase to ground fault, the algorithm of constructing B-phase transient current and furthermore constructing the exact zero-sequence current is founded out through the analysis in frequency domain and time domain, and the fault line-detection method can be actualized according to zero-sequence current's transient characters. Based on them, a new method used to identify single phase to ground fault line using transient characteristics in two TAs distribution networks is formed. The proposed line-selection method is not affected by the mode whether the Petersen coil exists at neutral and the unbalanced current under normal operation condition.