Research On Faulty Line Selection And Fault Section Location For Single-Phase Grounding Fault In Resonant Grounding System

When short circuit faults occur in medium voltage distribution networks,the proportion of single-phase ground faults is the highest.When a single-phase grounding fault occurs in a resonant grounding system,the short-circuit current is small,and the three-phase line voltage is still symmetrical,which can operate with a fault for about 2 hours,therefore,the power supply reliability is high.However,if the fault is not cleared in a timely manner,it may lead to insulation breakdown between lines and develop into a phase-to-phase short circuit fault,which will expand the fault range.At present,the resonant grounding method in which the neutral point is grounded through the arc suppression coil is more and more widely used,and the distributed power generation and cable-overhead hybrid lines are increasing in the distribution network.Due to the ground fault is easily affected by the onsite environment,the success rate of faulty line selection and fault section location is not high.To address these problems,this paper studies the line selection method and the fault section location method for quickly identifying the fault when a single-phase grounding fault occurs in a resonant grounding system based on the dynamic time warping(DTW)distance algorithm,and combined with DTW distance coefficient and fuzzy C-means(FCM)clustering.In this way,the safety and reliability of the distribution network operation can be improved.This paper analyzes the resonant characteristics of single-phase grounding fault in resonant grounding system,and determines the characteristic frequency band with rich transient information.The difference of steady-state and transient fault characteristics between the faulty line and the non-faulty line,the upstream and the downstream of the fault point in the characteristic frequency band is analyzed,which is used as a basis for identifying the faulty line and locating the fault section.Aiming at the problem that most faulty line selection methods are easily affected by the impact of transition resistance,noise and other factors,resulting in a low success rate in faulty line selecting,a faulty line selection method based on DTW distance is proposed.Firstly,the quantitative product of the transient zero-sequence current of each line and the transient zero-sequence voltage of the busbar is calculated to enhance the strength of the fault transient signal.Secondly,the DTW distance algorithm is adopted to form the DTW matrix,and the DTW distance coefficient of each line is calculated.Select the first three with larger coefficients,if the largest coefficient is less than the sum of the other two coefficients,it is judged as a bus fault,otherwise it is judged as a faulty line.Finally,the proposed fault line selection method is verified by simulation and field recorded data under various fault conditions,and the results show that the proposed method can reliably select the faulty line under various fault conditions.Aiming at the problem of low accuracy of fault location in the existing fault location methods due to the access of distributed power sources and the increase of cable-overhead hybrid lines,a fault section location method based on DTW distance is proposed.Firstly,the quantitative product of the transient zero-sequence current at each monitoring point of the fault line and the transient zero-sequence voltage of the bus is calculated to enhance the strength of the transient signal.Secondly,the DTW distance between the transient signals at both ends of each section is calculated,and FCM clustering is adopted to cluster and divide the DTW distance of each section to obtain a membership matrix and cluster center.If there is self-contained data in the membership degree matrix,the section corresponding to the data is a fault section,while the sections corresponding to all other data are determined as nonfault sections.If there is no self-contained data in the membership matrix,it is determined that a fault has occurred at the end of the line.Finally,the effectiveness of the proposed fault location method is tested by simulation under various fault conditions,and the reliability of the location method is also verified by on-site recorded data.