Abstract: Abstract: According to the fault characteristics of single phase high impedance grounding of resonant grounding system,wavelet packet analysis and energy entropy are combined to analyze the transient zero sequence current,set the energy entropy be the transient characteristic of single phase high resistance ground fault,so we can analyze the uncertainty of transient fault quantitatively. 1. Transient analysis of single-phase ground fault 1.1 The fault feature 1) under-damped 2) over-damping In both cases above,the fault condition that affects the transient current characteristic of zero sequence mainly depend on the transition impedance and grounding moment. 1.2 The simulation verification When the grounding point of voltage in the phase at 90°,the zero sequence transient current is mainly the capacitive component of high frequency oscillation.When the grounding point of voltage in the phase at 0°,the zero sequence transient current is mainly the attenuated inductive dc component. 2. High resistance fault line selection method for resonant grounding system 2.1 Analysis tool for high resistance fault characteristics Wavelet packet The wavelet packet analysis is performed for the zero sequence current signal,and calculating the corresponding energy of each sub-band signal.The expression is: 2.2 Energy entropy analysis of zero sequence transient current shannon comentropy Information entropy solves the problem of quantization measurement of information, which is borrowed from thermodynamics.We apply information entropy after the event of a high impedance fault to analysis of the zero sequence current,according to the wavelet packet decomposition under the specified scale coefficient, on the basis of power spectrum, define the concept of energy entropy.The energy entropy at the j scale is: 3. Single phase high resistance ground fault mode classification 3.1 The average energy entropy of the line There are n lines in the bus bar, define the energy spectrum entropy measure S: 3.2 Failure mode classification 1) High frequency failure mode Fault phase is generally greater than 20°. 2)Low-frequency failure mode The single-phase earth fault occur in the voltage phase at 0°. 3.3 The method of judging different fault modes 1)When S>1 Determining a high frequency fault,zero sequence current energy is concentrated in the high frequency band.At this time, we use the method of correlation to analyze and select the line data. 2)When S<1 Determine low frequency fault,the transient energy of each line is mainly concentrated in the working band.At this time, we make zero sequence current pass the zero sequence current through the low pass filter,then the most energetic line is the fault line. 4. The simulation results of the circuit φ/（°） R/（Ω） Failure mode The calculation results 0 3 2.7e-4 Low frequency 5.46e7,3.44e4, 5.07e7 6 2.0e-4 Low frequency 7.5e7,1.9e7 , 2.5e7 20 3 1.15 Low frequency 6.7e9,2.2e9 , 1.6e9 50 3 2.28 High frequency -0.73, -0.31, -0.34 6 2.96 High frequency -0.76,-0.27 , -0.32 80 3 4.21 High frequency -0.82,-0.22, -0.24 6 5.35 High frequency -0.81,-0.21, -0.23 5. Conclusion This method can judge the high resistance faults of different fault types and draw the correct conclusion.