Study On Fault Location Of Cable Hybrid Line Based On Traveling Wave Energy Variation

Compared with overhead transmission lines,hybrid transmission lines are formed by alternately connecting two types of lines,which makes its structure more complicated and makes it difficult to locate faults accurately.From the propagation characteristics of traveling waves,due to the different line parameters of overhead lines and cable lines,the wave speeds on the two types of lines are inconsistent,and the wave impedance before and after the connection point is discontinuous.Therefore,the existing method cannot be directly applied to the fault location of the hybrid line.The transmission line is the cornerstone of the power supply system and plays a central role in the transmission of electrical energy.Fast and reliable location of transmission line faults is an inevitable requirement to ensure stable operation of the power system.In this paper,the generation process of the fault traveling wave is firstly explained in principle,the amplitude and phase changes of the traveling wave propagating on the lossy line are studied,and the traveling wave refraction phenomenon at the discontinuity point of the wave impedance is analyzed.Secondly,the frequencydependent characteristics of the line parameters are used to explain the causes of the traveling wave dispersion phenomenon,and the differences in the propagation characteristics of traveling waves at different frequencies are analyzed,which illustrates the necessity of time-frequency domain decomposition of traveling waves.Finally,for the simplified six-conductor coupling cable model,starting from the demand,the inherent characteristics of the high-voltage cable frequency change parameters are analyzed,and the decoupling method that is not affected by the cross-connection point of the cable is derived.Based on the above research,a unified positioning model for overhead lines and cables was constructed.Based on the above theoretical research,this paper expounds the concept of traveling wave energy from the perspective of electromagnetic field,and analyzes the particularity of the common A-type and B-type cable hybrid line structures based on the catadioptric and attenuation characteristics of traveling wave energy.A fault segment identification method based on traveling wave energy ratio is proposed.This method is based on the principle of basic catadioptric reflection of traveling waves,and utilizes the change of traveling wave energy caused by the special structure of cable connection points to analyze the traveling wave energy ratio at both ends of the line under different fault locations to construct the segment positioning criterion,Can directly identify the fault of the cable connection point,and significantly distinguish the overhead line fault from the cable fault.Finally,build a line model for simulation,verify and analyze the impact of fault type and fault conditions on section discrimination.On the basis of the fault section location,this paper fully considers the attenuation characteristics of traveling wave energy,and quantitatively derives the mapping relationship between traveling wave energy at both ends of the line and different fault locations for cable hybrid lines with different structures.Iterative precise positioning method based on the initial traveling wave energy of the downward wave component at the same frequency.Considering that S-transformation cannot accurately extract a single frequency component in a multi-frequency aliasing traveling wave signal,Stransformation errors must be introduced during signal processing,which affects positioning accuracy.To solve this problem,the correspondence between traveling wave energy attenuation coefficient and traveling wave propagation distance is obtained through model simulation and numerical fitting,which indirectly reflects the S-transform error at different propagation distances,so as to correct the error during the positioning process.This method is based on the initial traveling wave propagation path of five types of faults,and fits the variation law of the six types of traveling wave energy attenuation coefficients.The mathematical relationship fitted is only related to the fault location and line structure,and has nothing to do with the line length.Mixed lines composed of various types of lines;At the same time,in principle,this method greatly reduces the systematic errors introduced by the data processing process by fitting the key factors.Compared with the traditional positioning method,it can further improve the accuracy of fault location.This paper builds a mixed line simulation model in PSCAD / EMTDC and simulates different types of faults in different line sections.Simulation experiments verify the feasibility and robustness of the algorithm.The thesis contains 69 figures,28 tables and 96 references.