Study On Single Phase To Ground Fault Location In Distribution Network With Flexible Neutral Grounding

With the development of the information and intelligent engineering construction of the distribution network in China,fault location technology is of great significance to quickly find faults,shorten the time to restore normal system power supply and reduce social and economic losses.The vast majority of faults are single-phase grounding faults.Therefore,achieving distribution network especially the accurate single-phase grounding fault location,can facilitate the maintenance personnel to repair the fault in time,find local insulation defects,and maximally avoid the occurrence of cascading faults or even blackouts,which has far-reaching significance for improving the safety,stable operation and power supply reliability of distribution network.Due to the advantages of flexible grounding mode,which is only limited to tripping for the permanent grounding fault,and for the instantaneous grounding fault without interrupting the power supply to users,the distribution network with high reliability requirements of power supply has begun to apply the flexible grounding mode.Based on this,this thesis studies the single-phase grounding fault process,fault section location algorithm and accurate fault location algorithm of flexible grounding distribution network.By setting zero sequence and negative sequence current measurement nodes at the branch of line and negative sequence voltage measurement nodes at the end of line,the system is divided into three regions,and each region is set with an edge node.The fault location in flexible ground distribution network is realized by the way of coordinating the distributed measurement nodes and edge nodes.There is no need to measure the zero-sequence voltage,as well as synchronously measure of the zero-sequence current and negative sequence current.In addition,the sampling frequency is low.It can better adapt to the operation characteristics of flexible grounding distribution network while arranging the least measuring equipment.Firstly,this thesis introduces the advantages of flexible grounding system which combines arc suppression coil and small resistance grounding,and describes its working principle and action logic after fault in detail.Secondly,the distribution of zero sequence current is described after fault in flexible grounding system.Meanwhile,the characteristics are summarized,which are zero sequence current of fault line and nonfault line before and after parallel connection of small resistance.Finally,the fault transient circuit is analyzed.The transient zero sequence current is divided into transient capacitive current component and transient inductive current component,and their differences in amplitude are analyzed.Aiming at fault section location of flexible grounding system,considering that flexible grounding is the combination of small resistance and arc suppression coil neutral grounding,the characteristics of single-phase grounding fault are analyzed.From the aspects of amplitude and phase,the negative sequence voltage variation and zero sequence current correction projection coefficient are taken as the characteristics of section location,and SVM(support vector machine)is used in nonlinear classification.Based on the function of pattern recognition,a SVM section location algorithm based on negative sequence voltage variation and zero sequence current projection is proposed.At the same time,the system is divided into different regions and the edge nodes are arranged.The edge computing which is more effective than cloud computing is used to process data,so as to reduce the amount of data storage and calculation,and improve the speed of fault section location algorithm.By building the IEEE34 node model for simulation,the influence of fault conditions on section identification is verified and analyzed.It is proved that the negative sequence voltage variation and modified projection scale coefficient defined in this thesis can comprehensively utilize the fault information of flexible grounding system,and improve the accuracy and reliability of section location algorithm on the basis of ensuring the rationality of SVM characteristic quantity.Aiming at the accurate fault location of flexible grounding system,an accurate fault location algorithm based on negative sequence voltage variation is proposed.In the off-line state,the least square method is used to set the iteration interval of virtual fault nodes in each line section.After the fault occurs,the deviation between the calculated and actual changes of the negative sequence voltage during iteration of each virtual fault node is obtained in the fault section.The abnormal data and the measurement data with measurement error are considered for data adjustment,and the corrected failure probability is obtained.The precise location algorithm uses few measuring nodes in the fault area and the computation scale is small.The simulation results of IEEE34 bus system show that the proposed method has small positioning error and high reliability in the presence of bad data and high resistance fault.The thesis contains 32 figures,13 tables and 89 references.