Research On Line Selection And Location Of Single-phase Ground Fault In Distribution Network Based On Wavelet Energy Coefficient Of Variation

Among all kinds of fault statistics of distribution network,the probability of single-phase ground fault is the highest,and with the continuous expansion of distribution network scale,the fault point capacitance current increases gradually,which is easy to cause arc grounding,which may lead to the expansion of fault range and threat to distribution network security.Therefore,it is very important for the safe operation of the distribution network to detect the line and location of the fault quickly and accurately.This paper analyzes the characteristics of the steady-state and transient state of the single-phase ground fault of the distribution network,and compares and verifies the theoretical and simulation aspects of the zero-sequence current change of the faulted line and the non-faulted line.According to the difference in the electrical characteristics of the line after a fault in the distribution network,the zero-sequence current in the line is transformed by wavelet packet transformation,the reconstruction coefficient of a specific frequency band is extracted,the energy in the corresponding frequency band is calculated,and the relative power that can quantify the degree of difference between different signals entropy defines the comprehensive wavelet entropy.Based on the detailed analysis of fault transient characteristics,combined with the comprehensive wavelet entropy which reflects the difference degree of zero sequence current of different lines,the method of fault line selection based on the comprehensive wavelet entropy coefficient of variation is adopted in this paper.First,obtain the corresponding comprehensive wavelet entropy of each line,calculate a group of variation coefficients of the comprehensive wavelet entropy,and compare them with the threshold value,then judge whether there is abnormal value in the data group.If the coefficient of variation is greater than the threshold value,it indicates that there is abnormal value in the data group,and the maximum value in the data group is the abnormal value,and the corresponding distribution network line fails,otherwise,there is no abnormal value in the data group,the bus has failed.Based on the realization of single-phase ground fault line selection,the change of transient zero sequence current at different nodes in the fault line is compared and analyzed.It is found that the change of transient zero sequence current at the same side node of fault point is small,while the difference between nodes at different sides of fault point is large.In this paper,a method based on the coefficient of variation of adjacent wavelet entropy is used to locate the fault.Through wavelet packet transform of transient zero sequence current at different nodes in the fault line,combined with relative entropy,the adjacent wavelet entropy corresponding to two adjacent nodes is constructed.Then,the outliers of a group of adjacent wavelet entropy corresponding to adjacent nodes in the line are analyzed to determine whether there are outliers in the data group,if there is abnormal value in the data group,the line section fault corresponding to the value;otherwise,the end line section fault.In this paper,the simulation software MATLAB is used to build a 10 k V distribution network model.By setting different fault distance,transition resistance,fault initial angle and other conditions,the fault line selection and location methods used in this paper are simulated and verified.The simulation results show that the proposed method can realize fault line selection and fault location accurately.