The Research On Fault Line Selection And Location Of Small Current Grounding System

With the rapid development of economy,electric energy as clean and environmentally friendly secondary energy changes our life.In recent years,With the development of electric power industry by leaps and bounds,the grid structure is complicated,the installed capacity is increasing,and with the UHV transmission line full completion of the transmission line after a failure in all walks of life will be affected.In China,the small current grounding mode is widely used in the distribution network.When the system is in the ground fault,it is the key to restore the power supply quickly and accurately.In this paper,the characteristics of ground fault in the system are analyzed.Firstly,the line selection methods based on steady state component and transient component are introduced in detail,such as the amplitude ratio method,the five harmonic method,the zero sequence admittance method,the energy method and the wavelet analysis method.Through the simulation to verify and summarize the scope and limitations of each line selection method,we can get a conclusion that there are some shortcomings and limitations.In this paper,a method based on extreme learning machine is proposed in this paper,which can not adapt to a variety of single phase to ground faults.Firstly,the small current system model of 110/35 kV is established in Matlab,and the feature components are extracted by wavelet packet transform algorithm.Based on zero sequence admittance method,adaptive filter,PLL five harmonic analysis in different grounding system,grounding resistance of different fault types of the transient characteristics,using extreme learning machine method for fusion line selection,and with other fusion methods for comparison in line selection.The transmission voltage level is more and more high,the transmission capacity is also increasing,the transmission line failure,timely and accurately find the point of failure can not only reduce the number of transport inspection personnel's workload,but also restore the power supply in time.In this paper,by using the principle of single ended voltage reverse traveling wave location,a small current system model in Matlab has been built,The opposite traveling wave has been obtained using Hear wavelet decomposition of 3 layers.Through a large number of data,the method can be verified with high positioning accuracy,absolute error and relative error being calculated and factors leading to errors concluded.