Traditional transient mechanism based on the charging and discharging of distributed capacitance to earth for single-phase earth faults in non-solidly earthed networks has not yet been analyzed and validated strictly in theory or field. The traditional mechanism only partly reflects the resonance of transient processes and therefore is not accurate or comprehensive enough. A transient mechanism based on LC resonance for single-phase earth fault in non-solidly earthed networks is proposed. Based on the established single-phase earth fault model using distribution line parameters

the impedance characteristics of the frequency-dependency between different modes and different lines in the same mode(the impedance characteristic will alternately appear to be capacitive and inductive)are analyzed. The LC series/parallel resonance conditions and the energy exchange law between capacitive lines and inductive lines are given. A study has found that the transient process of single-phase earth fault can be produced by LC series or parallel resonance in single line

different lines in the same mode

as well as LC series resonance between different modes. The transient current produced by the main resonance(smallest resonance frequency in all the LC series/parallel resonance)contains clear fault location information.