Electric transmission line phase fault distance protecting method

The invention discloses an electric transmission line phase fault distance protecting method. According to the electric transmission line phase fault distance protecting method, additional fault impedance caused by a transition resistor is worked out through electric capacity between fault phases; line fault impedance from a transmission-line relay location to a phase fault point is obtained through difference between the ratio between the voltage between the fault phases and the current between the fault phases and the additional fault impedance, whether amplitude of the additional fault impedance line fault impedance from the transmission-line relay location to the phase fault point is less than line fault impedance from the transmission-line relay location to a protection setting range location is judged, and when the amplitude of the additional fault impedance line fault impedance from the transmission-line relay location to the phase fault point is less than the line fault impedance from the transmission-line relay location to the protection setting range location, a protector sends out a motion trip signal. The electric transmission line phase fault distance protecting method overcomes influence of the additional fault impedance caused by the transition resistor on distance protection motion performance between the phases. The electric transmission line phase fault distance protecting method can right and correctly motion and will not reject motioning or motion mistakenly when short-circuit fault of a transmission line interphase high resister occurs.