Research On Fault Location Of Hybrid Line Based On Empirical Wavelet Transform

With the continuous advancement of urban modernization,the proportion of line cable hybrid transmission line structure in the distribution network has increased significantly.In order to reduce the operation cost of distribution network,overhead lines are often used for power transmission outside the city,and cable lines are often laid in the city for power transmission,which has high power supply reliability,small maintenance workload,beautifying the city appearance and saving land resources.Traveling wave fault location technology has many advantages,including not affected by system oscillation,current transformer saturation,transition resistance and long line distributed capacitance,so traveling wave method is selected to locate the fault of hybrid lines in this thesis.Based on this,this thesis takes the small distribution network with three outgoing lines as the research object,extracts the fault current traveling wave by making the difference between the transient zero sequence current before and after the fault occurs,and studies the fault line selection and fault location method for single-phase to ground fault of hybrid lines based on empirical wavelet transform.The main research contents are as follows.(1)This chapter briefly analyzes the electrical quantities when single-phase grounding fault occurs in the distribution network of power system,and builds the simulation model of single ended power supply small distribution network system with three outgoing lines in Pscad.Empirical wavelet transform is used to decompose the traveling wave of fault current when single-phase to ground fault occurs in distribution network to obtain the low-frequency component,and then fault line selection is carried out for the simulation model of distribution network according to the criterion of low-frequency component line selection;fault location mainly adopts the principle of single terminal traveling wave,through singularity detection of low-frequency modal component,the fault line is accurately calibrated by vernier scale The accurate fault distance can be obtained by calculation.(2)An energy entropy line selection criterion based on empirical wavelet transform is proposed.An engineering simulation model of a small distribution system with three outgoing lines is built in Pscad.The empirical wavelet transform is used to decompose the fault current traveling wave of the fault line adaptively to obtain each mode component(IMF),and then the energy entropy of each outgoing line is calculated.According to the energy entropy criterion,the correct line selection of the fault line is realized.(3)Aiming at three section hybrid transmission lines,a two terminal traveling wave fault location method based on empirical wavelet transform is proposed.After the fault current traveling wave is extracted,the empirical wavelet decomposition is used to get the highfrequency component.Through the waveform analysis of the high-frequency component,the time when the fault traveling wave reaches the bus at both ends is obtained,and the fault section can be obtained by the difference calculation.Finally,the two terminal ranging principle is used to measure the distance.The simulation results show that the proposed low-frequency component line selection criterion based on empirical wavelet transform and energy entropy line selection criterion can be used in the distribution network system reliably;the single and double terminal traveling wave fault location method based on empirical wavelet transform proposed in this thesis has small ranging error and can be used in engineering practice.