| Line fault location comes into being a highly valued subject under the requirements of the security,the reliability and the economical operation in the power system.In the small current grounding system of the distribution network,single-phase earth fault has the highest probability of occurrence in fault types and its positioning technology has always been a difficult problem in the field of research.Due to the structure of the distribution network and its unique operating,the studies about the fault location of traveling wave is not enough,some problems of the traveling wave have not been solved well.The key technology of fault location is to detect the arrival time of traveling wave,whether the traveling wave head can be accurately detected will directly affect the positioning accuracy of the traveling wave fault location.Therefore,this paper studies the traveling wave detection method on the small current grounding system to solve the difficult positioning problem in single-phase earth faults.Firstly,aimed at the defects such as the lack of envelopes and modal aliasing in the empirical mode decomposition(EMD),the principle of Variational Mode Decomposition(VMD)is studied deeply.The VMD method is used to simulate and analyze the decomposition of the signal,the results show that the VMD method can accomplish the frequency separation and overcome the modal aliasing,it performs better in the non-stationary signals.By analyzing the characteristics of Teager Energy Operator(TEO),the calculation is small,which is suitable for real-time detection of signal,Aimed at the problem that the Hilbert Transform(HT)method is inefficient,a single-ended traveling wave detection method based on VMD-TEO is proposed.From the perspective of wavelet,the traveling wave signal is analyzed in detail and the method of wavelet transform is introduced into the transient traveling wave characteristic analysis,which brings great convenience to the study of traveling wave location.the detection results of Wavelet transform method and VMD-TEO traveling wave detection method are compared in the simulation examples.Secondly,for the shortcomings of steady-state information selection,this paper applies transient current traveling wave combined with wavelet analysis for the fault line selection of small current grounding system.The polarity and amplitude characteristics of the initial current traveling wave of the fault line and the non-fault line are studied and analyzed firstly,the line selection criteria is determined by the conclusion that the linear and null components have obvious difference characteristics in polar and amplitude,.Then,the time,amplitude and polarity of the transient current are taken as the starting point,the multi-level decomposition of the signal and the multi-scale comprehensive selection of the selected line result improve the accuracy of the line selection to a certain degree,configuration of different current transformers are met by using the selected line mode component or zero modulus component.Again,for the problem that the time difference required for ranging is not easy to obtain,single-ended traveling wave ranging method and wavelet analysis are used to carry out the extraction of faulty transient line in this paper.First of all,for the fault current signal phase mode transformation,the analysis shows that the linear mode component parameter is stable and the signal is easy to detect,for the signal analysis,the modulus component is chosen.Then,the main factors influencing the reliability of fault location are analyzed theoretically and the influence of waveform changes on the distance measurement is analyzed.Finally,select the appropriate wavelet basis function,decomposition scale and the a wavelet transform method for signal singularity detection to extract the maximum value of the model of the fault traveling wave signal,and to determine the exact timing of the occurrence of line failure,and then to achieve the purpose of precise positioning.Finally,a single-ended traveling wave ranging method based on VMD-TEO is a big innovation proposed in this paper,which has not been reported in the literature of small current grounding system and single-ended traveling wave detection in distribution network.In this method,the VMD decomposition of is used to select the high-frequency modal component and calculate the instantaneous teager energy value to achieve fault location,this method has a short computation time,it is very consistent with the real-time requirement of traveling wave fault location.Two kinds of positioning methods are used to analyze the data under certain parameters at last.The simulation results verify the correctness and effectiveness of the proposed method,and accuracy of fault location is higher. |
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