Abstract: Traditional Summation impedance protections are of great sensitivity towards single phase-grounded high-resistance faults, but cannot realize faulted phase selection tripping, and fail to reflect extremely-low-resistance faults. The latest research has made targeted improvement on the above two defects, but the performance is still not satisfactory. Therefore, this paper analyzes the mechanism of the inappropriate action of the existing summation impedance criteria. On its basis, a novel summation impedance criterion based on fault components is proposed to response sensitively to extremely-low-resistance faults. Further, an integrated summation impedance protection which consists of three types of summation impedance criteria is constructed, acquiring the ability of faulted phase selection tripping. The simulation results show that the proposed protection has significantly overcome the inherent defects of traditional ones, realizing the full coverage from metallic to high-resistance faults with correct phase selection, and hence can undertake transmission line main protection independently.