Research On Feature Extraction And Location Method Of Small Current Grounding Fault

The medium voltage distribution network in China generally adopts the operation mode of small current grounding(neutral point ungrounded or neutral point through arc suppression coil grounding).Due to the weak fault current,unstable arc and other factors,the fault characteristics are difficult to be effectively extracted,and the problem of small current single-phase grounding fault location has not been thoroughly solved.Aiming at the above problems,this paper focuses on the feature extraction method and fault location method of small current grounding fault.Firstly,the existing common small-current ground fault location methods and their advantages and disadvantages are analyzed and compared.The difficulties existing in the accurate positioning of small-current ground faults are discussed.The steady-state and transient process of a single-phase ground fault in the non-grounded neutral mode of a small current grounding system were detailed analyzed,as well as the same process of a single-phase ground fault in the arc suppression coil grounding mode of a small current grounding system were also analyzed.The characteristics of the fault in the steady-state and transient process were summarized.The single-phase ground fault simulation model for the small-current grounded system was established.Secondly,the characteristics of small current single-phase ground faults are extracted by using the skewness coefficient,and a fault location method based on skewness coefficient is proposed.The basic concept of the skewness coefficient is introduced,and the skewness characteristics of the zero-sequence current in each section of the normal line and the faulty line are analyzed.The zero-sequence current skewness coefficient of the feeder terminal(FTU)on both sides of the normal line and the normal section on the fault line is the same number,while the zero-sequence current skewness coefficient of the FTU on both sides of the fault section on the fault line is different.Using this characteristic,the location of the small current ground fault is realized.The simulation results based on Matlab software show that the fault location method based on the skewness coefficient is clearly characterized and can accurately locate the fault section under the different fault closing angle,different transition resistance,noise interference and different compensation degree of arc suppression coils.The positioning accuracy of this method is better than the fault location method based on transient correlation analysis.Finally,using dynamic time warping(DTW)distance to measure the similarity of the zero-sequence power at each detection point,a single-phase ground fault location method for distribution network based on DTW distance of transient zero-sequence power is proposed.The basic principle of the DTW distance is introduced,and the zero-sequence power characteristics of each detection point on the fault Iine after fault occurrence are analyzed.The DTW distance of the transient zero-sequence power of the adjacent two detection points on the fault line is obtained,and the calculated DTW distance is compared with the set threshold value.If the DTW distance is greater than the threshold,the fault section is determined,and the other is the normal section.The method does not require strict time synchronization of data uploaded from each detection point.It has good resistance to synchronization error and does not require high communication capability of the system.The simulation results based on Matlab verify the feasibility and effectiveness of this method under different fault conditions.