Analysis Of Fault Characteristics And Research On Fault Location For Distribution Network With Complex Grounding Mode

Widely distributed distribution network always operates in complex environment.Power outages caused by frequent random failures have resulted in significant economic losses.Building a strong and safe distribution network is an important part of the national development strategy of “developing smart grid and distributed energy”.Neutral grounding mode of distribution network which is closely related to its safe and reliable operation has attracted much attention in the construction of city grid and rural grid.With the expansion of the scale of distribution network and the enhancement of the ratio of city cables,the complicated situation that a variety of grounding modes coexist and safety control strategies diversify has appeared.For single-phase grounding fault with high proportion in distribution network,the characteristics of grounding fault current in non-effective grounding distribution network is weak so that it's difficult to detect,and zero sequence current protection is not sensitive enough in effective grounding distribution network when grounding fault with high resistance happens.Incorrect line selection and trip operation will lead to the expansion of power outages and casualties.In addition,complex multi-branch structure of distribution lines cause a lot of trouble for fault finding.Therefore,how to carry out accurate fault analysis and adopt reliable protection measures for distribution grid with different grounding methods is widely concerned at home and abroad.The current simulation model for study on ground faults of distribution network are often too simple,including the problems of the incomplete access devices,the oversimplified network structure and the incorrect components parameters is not comprehensive enough,the network structure is too simple,parameter is not accurate enough,which may lead to incorrect understanding of electrical characteristics of grounding fault.Aiming at single-phase ground fault analysis,on basis of extensive investigation of typical network structure and access equipment,equipment selection and parameter calculation is carried out according to the design standard and specification.Then a system simulation model reflecting the engineering practice is established by adopt accurate element and the network model.What's more the influence of access equipment on grounding fault is defined.Typical neutral grounding mode includes isolated neutral,arc suppression coil grounded and low resistance grounded.In recent years,in order to solve the problems of arc suppression and line selection accuracy of classic grounding,composite grounding arc-suppression modes have been proposed,such as grounding fault transfer mode and intelligent multimode grounding mode,but leaving the mechanism of action to be analyzed.In this paper,single-phase grounding fault under typical neutral grounding mode is analyzed and simulated,and the influence of transition resistance on steady and transient characteristics is analyzed emphatically.This paper also analyzes transient fault process of the two composite grounding arc-suppression modes by simulation and illuminates the transient characteristics of the operation process.In addition,a line selection method based on the first transient half wave of fault grounding and operation grounding of the own line is put forward for grounding fault transfer mode.Complex structure and a large number of distributed generators of modern distribution network deteriorate the transient process.The current line selection protection device influenced by complex fault characteristic,fault resistance,line parameters and other factors has low accuracy of line selection.Traveling wave line selection method is not affected by the grounding mode and the above factors,and also can accurately determine the fault section.So it has achieved much attention in recent years.In this paper,the line selection of traveling wave method based on artificial intelligence and the fault region judgement method of traveling wave based on fusion of multi-terminal data for grounding fault are proposed.The line election method of traveling wave selects voltage traveling wave of zero mode as time detection basis.The neural net is trained by the classified relative fault time array produced by fault simulation.Then the line selection result can be obtained by inputting test sample into the net.After distinguishing the fault line,the fault region judgement method of traveling wave calculates fault distance through the fusion and filtering estimation of measurement data based on Kalman filtering algorithm and least square method.Combing with the graph theory description of topology,the accurate of fault section can be located accurately.Finally,simulation results demonstrate the effectiveness of the two methods.