The factors affecting the frequency of the free oscillation component of the tripping phase voltage when a single-phase grounding fault occurs in an EHV transmission line with shunt reactors are studied. The phase characteristics of the tripping phase voltage during transient single-phase grounding fault of EHV transmission line with shunt reactors are analyzed

and the reason for the phase periodic fluctuation of recovery voltage is revealed. With the consideration of the influence of the error of Fourier algorithm when processing the signals with non-based frequency components on tripping phase voltage calculation

the sum of healthy phase voltages is introduced as the polarization voltage

the phases of tripping phase voltage in transient faults and permanent faults are differentiated based on the polarization voltage

and a criterion of phase fluctuation of tripping phase to identify permanent faults is proposed.EMTP simulation shows that the proposed criterion is simple

accurate and immune to the transition resistance

and can be effectively applied to the fault nature identification of single-phase adaptive reclosing of EHV/UHV transmission lines with shunt reactors.