Make full use of fault transient information can improve effectively the accuracy of fault line selection in resonance earthing system. In this paper

a kind of line selection scheme using the difference in phase-frequency characteristics of zero-sequence impedance is proposed. The zero-sequence impedance after the fault of the single-phase earthing system of the resonant earthing system has a definite feature. The zero-sequence impedance of sound feeder is capacitive at any frequency band

while

the zero-sequence impedance of fault feeder is inductive at low frequency band

and capacitive in high frequency band. The dispersion analysis method is constructed of zero-sequence impedance angle of feeder at various frequency bands in accordance with above feature. It is known by the analysis that the dispersion of the zero-sequence impedance angle of the sound feeder is smaller and that of the faulty feeder is higher

particularly

the difference of zero-sequence impedance at high and low frequencies approaches 180 degree. On this basis

the criteria of fault line selection are constructed. It is shown by the simulation result that the method is still effective in high impedance earthing and

compared with the traditional line selection method

improves the accuracy and reliability of line selection.