Research On Fault Line Selection Of Single-phase Grounding Fault In Small Current Grounding System

At present,small current grounding system is widely used at China's medium voltage power grid,which could effectively improve the reliability of power supply systems.But since its fault current is not large,so that it will increase the difficulty of single-phase grounding fault line selection.Currently,line selection methods based on single signal are widely used in small current grounding system both at home and abroad.However,they have many limits: these methods are difficult to cover all of the grounding conditions in practical application.What's more,they are easy to be affected by external uncertainties.Therefore,line selection is making intelligent progress.Intelligent fault line selection methods theoretically have better self-adaptability and fault tolerance,which could greatly reduce the impacts of external interference and improve the accuracy of fault line selection.But intelligent methods require large number of actual samples data generated by single-phase grounding fault occurring in power grid.In this case,a monitoring device for small current grounding line selection with wave recording function can provide training and testing samples for intelligent line selection,so our device could provide a reliable basis for the development of small current grounding line selection methods,and then we can improve or even propose a new line selection method.First of all,this thesis describes the significance and research status of single–phase grounding fault line selection methods in small current grounding system.The fault analysis of small current grounding system with different neutral grounding modes is carried out.Through the description of their fault characteristics,the single line selection methods based on steady-state signal or transient-state signal are introduced and summarized respectively,what's more,the advantages and disadvantages of these methods are analyzed by simulation experiments.Then,it points out that fault line selection methods in small current grounding system are turning to be intelligent.Secondly,this paper summarizes the advantages and disadvantages of the existing synthetic and intelligent fault line selection methods.After analyzing line selection algorithm based on modern signal processing technology,it notes that intelligent fault line selection methods require large number of actual samples data generated by single-phase grounding fault.At last,a monitoring device for small current grounding line selection with wave recording function was designed in this thesis and it saved large amounts of small current grounding fault samples data.Furthermore,it carried out offline analysis for the samples data.Simulation experiments and tentative operation have verified that the monitoring device designed in this thesis is suitable for small current grounding system with different neutral grounding modes...