Research On Line Selection And Location Of Single-phase Grounding Fault In Distribution Network With D

Small-current grounding systems are widely used in China’s medium-and lowvoltage distribution networks,but they are highly susceptible to single-phase grounding faults.The access of DG(Distributed Generation)makes the topology of small-current grounding systems change,resulting in changes in fault characteristics when singlephase grounding faults occur in the system.The traditional distribution network singlephase ground fault selection and location method may not be applicable to the distribution network with DG.In this paper,we analyze the characteristics of singlephase grounding faults in DG-containing distribution networks and conduct research on fault routing and location methods for DG-containing distribution networks based on the fault characteristics analysis.This paper first analyzes and summarizes the transient and steady-state fault characteristics of a small-current grounding system after a single-phase ground fault occurs.Taking photovoltaic power generation as the research object,a composite sequence network equivalent model is established for single-phase ground fault of distribution network containing DG,and the effects of DG access location and neutral grounding mode of grid-connected transformer on fault point current,positive sequence current,negative sequence current and zero sequence current are analyzed,and it is concluded that DG access changes positive sequence network and zero sequence network is related to neutral grounding mode.And the simulation is verified by Matlab/Simulink.The transient zero-sequence fault component is selected as the fault characteristic quantity,and based on the characteristics that the fault line contains a large amount of information and a large energy entropy value,a fault line selection method for distribution networks containing DG based on directional traveling waves and wavelet packet energy entropy is proposed.The method first extracts the three-phase current and voltage data to obtain the transient fault components,and performs phase mode transformation to obtain the directional zero-mode current traveling wave;uses db3 wavelet to decompose the reverse zero-mode current traveling wavelet and selects the wavelet packet coefficients of specific high frequency bands to solve the energy entropy;finally determines the fault line according to the energy entropy value of each line.The simulation experiments show that the proposed method is not affected by the transition resistance,DG access location,and fault distance.Traveling wave fault ranging has a very high speed and accuracy,and is not affected by external factors such as neutral grounding mode,system parameters,and line asymmetry,making it the most commonly used method for fault location.However,traveling wave fault ranging is influenced by wave speed,wavehead arrival time and total line length.This chapter analyzes the influence of power electronics in DG and the control strategy of the inverter on the traveling wave head,concludes that the selection of fault signal data with appropriate sampling frequency and frequency band can effectively avoid its influence,and proposes a double-ended traveling wave ranging method to eliminate the influence of wave speed.Firstly,the transient fault components are obtained from the three-phase current and voltage data,and the zero-mode current traveling wave is obtained by phase mode transformation.Then the db3 wavelet packet decomposes the zero-mode current traveling wave,selects the wavelet packet coefficients with appropriate frequency bands,determines the wavehead arrival moment according to its mode maximum point,and finally brings in the formula to calculate the fault distance.Simulation shows that this method in changing DG position different transition resistance value,different line types,different fault distance distance measurement results error is less than 500 m,has a certain engineering practical value.