Research On Single-phase Grounding Fault Line Selection Based On Time-Frequency Correlation Analysis

In China the medium voltage distribution power grid runs more in small current grounding mode,single-phase grounding fault is the most frequent fault,therefore it is of enomous significance for the safe operation of the power grid to realize single-phase ground fault accurate selection of the wire.In this paper,a new fault line sclection method is presented by studying the related characteristics of the time-frequency domain of fault signal.Based on the single-phase ground fafault zero-sequence network model of the small current grounding systems,the theoretical and simulation research on the characteristics of the fault line and the time-frequency domain of the sound line when the single-phase ground fault of the small current grouding system is carried out.The results show that there is a negative correlation between the partial frequeney components of the fault line transient zero-sequence current and the sound line transient zero-order current.Adaptive determinaion of feature extration frequency window is important to achieve accurate line selection.This paper also studies on the fault line selection method based on the relecant characteristics of the time frequency domain.To determine the reference line on the principle of non-frequency component energy and maximum,it uses wavelet coherence analysis as a mathematical tool,to analyze the transient zero-sequence current of each line afer failure,and uses the wavelet coherent spectrum as basis for establishing the characteristic time frequency winadow,to extract the average wavelet coherent phase of each line in the charateristic time-frequency window to from the line selection feature vector.Based on coarse error theory,a fault selection criterion based on the Grunbbs criterion if constructed,and the elements in the line selection feature vector are subjected to Grubbs test.The corresponding line of the element rejected by the Grubbs criteria is the fault line,and it there is no abnormal value in the Grubbs criterion,it is determined to be a bus line fault.In order to verify the relbbility of the fault selection method proposed an this paper,the 10kV distribution network simulation model was consructed by MATLAB/Simulink,and the simulation verification is carried out under different neutral point operation mode and fault conditions,and the fault selection method is verified experimentally by the laboratory 380V distribution network physical simulation system.Both simulation and experiment have verified the validity and adaptability of the proposed method.