Method for measuring phase to phase mutual impedance of long-distance extra-high voltage common-tower double-circuit transmission line

The invention discloses a method for measuring phase to phase mutual impedance of a long-distance extra-high voltage common-tower double-circuit transmission line. The method comprises the first step that the head end of a measured phase is in an open circuit, the tail end of the measured phase is in ground connection, the head ends of other phases are in an open circuit, the tail ends of other phases are in ground connection, voltages are applied to the head end of the measured phase, currents are injected into the head end of the measured phase, and the current signal of the head end of the measured phase and the induction voltage signals of the head ends of other phases under two frequencies are synchronously measured; the second step that the voltage signals and the current signals under the two frequencies are obtained through an FFT filtering algorithm; the third step that phase to phase mutual impedance values under the two frequencies are respectively calculated according to the voltage signals and the current signals under the two frequencies, and a phase to phase mutual impedance value under the frequency of 50Hz is obtained by averaging the two phase to phase mutual impedance values. According to the method, a traditional measurement method is changed, the influence of line distribution parameter characteristics and induction voltage phases and the existence of power frequency interference are considered in the line connection mode and the algorithm, and especially in the long-distance transmission line, the errors of the phase to phase mutual impedance value measured through the method are reduced, and engineering needs are met.