Research Of Single Phase Fault Line Selection Of Small Current Grounding System Based On Wavelet Correlation Analysis

In China,Small current grounding system is widely used in 35 kV and below distribution network,that is,neutral point is not grounded,and the ground system is grounded by arc suppression coil.Due to the diversity of the structural changes and the randomness of the faults,the probability of the single phase grounding fault is about80%.So far,the problem of fault line selection in the small current grounding system has not been completely solved.Therefore,when the fault occurs,how to accurately judge the fault line and quickly restore the normal operation has become an urgent problem to be solved at the moment.First,this paper introduces the purpose and research status of single phase fault line selection in small current grounding system,and gives the existing common method of line selection.The fault steady-state and transient characteristics are analyzed for the small current grounding system with different grounding methods.The fault model is established by using the software PSCAD that can analyze the electromagnetic transient process of the power system,and the simulation analysis is made to verify the accuracy of the model.Secondly,according to fault transient characteristics of transient process contains a clear law of high frequency information,because the wavelet analysis has the characteristics of time-frequency localization and multi-resolution analysis.The fault current signal can be decomposed into different frequency bands,so it can be used to analyze the transient signal.Then the theory of wavelet and wavelet packet analysis is introduced,and the principle of line selection is described,which provides a theoretical basis for the extraction of fault features and the selection of fault lines.Finally,this paper gives the line selection criterion and line selection procedure of fault line selection based on wavelet correlation analysis.First,the transient zero sequence current is divided into 4 layers by wavelet packet to determine the frequency band corresponding to the maximum energy value,and the correlation coefficient of each line path is obtained by correlation analysis,and the comprehensive correlation coefficient of the line is obtained,and then the maximum of the comprehensive correlation coefficient is compared.The result of the minimum difference is then compared with the fixed thresholdto determine the fault line.Then through the simulation model established by PSCAD,the simulation analysis of the neutral point through arc suppression coil grounding system and the concrete example of the busbar fault shows that the wavelet correlation analysis method used in this paper can be more rapid and reliable to select the fault line.