The invention discloses a line single-phase earth fault positioning method based on the before-and-after fault
voltage phase characteristic. The line single-phase earth fault positioning method includes the steps of firstly, measuring a fault-phase
voltage, a fault-phase current and a zero sequence current at the protection installation position of an electric
transmission line, measuring voltages of the other two normal phases, calculating a fault-phase
voltage when the electric
transmission line normally operates in real time through the voltages of the two normal phases after line single-phase earth faults, sequentially calculating a
phase angle of the fault-phase voltage of each point on the electric
transmission line and the fault-phase voltage, when the electric transmission line normally operates, of the point of the electric transmission line in the mode of beginning with the protection installation position of the
power transmission line and gradually increasing with a fixed step length, and achieving accurate
ranging of the electric transmission line single-phase earth faults through the characteristic that the angles of the fault-phase voltages in front of and behind a fault point and the fault-phase voltage when the electric transmission line normally operates can generate
phase step changes. According to the line single-phase earth fault positioning method, the fault-phase voltage before the line single-phase earth faults is not required to be memorized, a loop for keeping the voltage before the line faults is not required to be set, influences of transition resistance and a load current are eliminated, and the
ranging accuracy is high.