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Distance relay is the main protection of power transmission lines and make an important role in power system stabilization if it operates selective and instantaneous. In this paper, the trajectory of the fault impedance is determined. It is shown that in the end of the first zone or in the middle of the second zone, distance relay could not make a correct decision for operating if the fault occurs with arc. So to overcome this problem, in this paper a novel technique using total harmonic distortion (THD) is proposed. The proposed method makes the distance relay more selective and instantaneous.