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A single phase to earth fault location method in distribution network based on signal injection principle is proposed. It is expected to solve single phase to earth fault location problem in neutral indirectly earth system. When single phase to earth fault occurs, a sine current signal with constant frequency is injected into the fault phase from potential transformer's secondary side, the injected signal current and its voltage drop on the fault line can be measured through the fault line's zero sequence current transformer (CT) and potential transformer (PT) on the bus. Based on distributed parameter model of distribution line, we can get the relational expressions between injected signal voltage and current at measuring point and fault point, then, we can solve the fault distance by using the resistive characteristic of transition resistance. This method is not affected by system structure and operating mode, and the use of distributed parameter line model eliminating the impact of distributed capacitance, the result of fault distance has high precision. Simulation results verify the correctness and feasibility of the proposed method.