Research On Fault Identification And Location Of Distribution Cable Networks By Multisource Transient And Steady Data

With the acceleration of the urbanization process,power cables have been taking a large portion of the distribution lines.The overhead lines have been gradually replaced by the cables.The working environment of the cables is usually poor.They are prone to the faults due to the external forces,moisture,contamination,and internal defects.Accurate and reliable fault location is conducive to the rapid searching of the fault,significant improvement of the repairment work,and ensurance of power supply safety and reliability.However,the actual urban distribution network has lots of short cable branches.The internal structure of the distribution calble is complex,resulting in various fault types and fault feature variations,which poses a great challenge to fault location.The current methods can only locate the line section with a metallic grounding or short-circuit fault.They cannot locate the accurate fault point on line in a complex condition.In addition,the current fault location systems are commonly based on the centralized data processing platform.A large amount of data transmitted to the cloud server at the substation increases the communication pressure,reduces the efficiency of fault response,and decreases the data safety and system reliability.Aiming at the above problems,this paper conducts the research on the transient and steady analysis of the distribution cable network,fault feeder detection and section location,accurate fault location and design of the cloud-edge collaborative fault location system.Details are as follows.First,considering the structure and electrical parameters of the three-core cable widely employed in the distribution network,the steady-state equivalent lump-parameter circuit model of the three-core cable prior to and after a fault is constructed based on the classification and modelling of the cable fault.The distribution features of the voltages and currents in steady-state along the fault and healthy cables with the different neutral grounding modes are analyzed in theory.From aspect of the transmission equations,the feasibility of decoupling of the three-core cable in time and frequency domains is discussed and the general method for decoupling the transient signals in the three-core cable is then proposed.The propagation characteristics of the fault-featured voltage moduli in a single cable and the time-frequency features of the fault-featured current moduli in the whole network are summarized.Next,according to the variation of the fault-featured moduli before and after the fault,a fault detection method is presented for the distribution three-core cable.The formulas of the amplitudes of the frequency components in the transient fault-featured voltage moduli with the feeder or bus fault are derived in theory.A fault feeder detection criterion is then proposed based on the difference between the amplitude ratios of both ends of the feeders.The time-domain equivalent circuit model of the three-core cable is created to analyze the inner relationship between the grounding line currents and zero-sequence ones at the local ends of the cable feeders.Another fault feeder detection criterion is proposed based on the distribution features of the grounding line currents.On the basis of the time-frequency characteristic differences of the fault-feaured moduli in different line sections,a fault section identification criterion which integrates the amplitude and polarity features of the transient current frequency componnets is proposed.Then,based on the distribution of the steady-state voltage along the three-core cable in normal operation,the method for correting the synchronous error in the phasors at both ends of the cable is presented.According to the continuity principle of the voltages and currents along the cable after the fault,the fault phase idenitification criterion,fault resistance estimation formula,and fault distance calculation equation are proposed for the steady faults.Considering the differences of the measurement and synchronization levels in field,the fault distance calculation methods are presented for the transient faults by using the arrival time,polarity,and frequency component amplitude of the transient moduli.Finally,under the general framework of the edge computing in industrial field,an edge-cloud collaborative system applicable to the fault location in the distribution cable network is designed by considering the characteristics of the presented fault feeder detection,fault section identification and accurate fault location methods.Additionally,a comparison between the designed edge-cloud cooperative system and the current centralized system in substation is conducted to show the advantages,including the reduction of communication stress of the substation,improvement of system response speed,and ensurance of the system reliability.A simulation model of the typical 10 kV distribution cable network is established by PSCAD/EMTDC.The computation results of various fault simulation cases demonstrate that the proposed methods can rapidly detect the fault feeder,identify the fault section,and locate the fault point on line with high accuracy.The grounding modes of the network neutrals and fault initial conditions have little impact on the proposed methods.In most of the cases,the proposed methods,which are robust to noises,line parameter variations,communication delays,and protection operations,have high reliability.This thesis contains fifty-five figures,thirty-nine tables,and one hundred and seventeen references.