Research On Detection Method Of High Impedance Fault Of Distribution Line

The safe and reliable operation of distribution lines is related to the normal life of people and the power supply reliability of the power system.When a single-phase HIF(high-impedance-fault)occurs on the distribution lines,the traditional protection cannot effectively identify and timely remove the fault due to the small fault current.In order to solve this problem,the paper studies the single-phase HIF detection method for distribution lines of small current grounding system and small resistance grounding system.The fault characteristics of single-phase HIF in distribution network with different grounding modes are studied.Emmanuel model was used to simulate the distribution network high-resistance grounding fault,and the single-phase HIF simulation model of the distribution line with low-current grounding system(including non-ground neutral system and arc-suppression-coil-ground neutral system)and small-resistance grounding system were established on the Matlab/Simulink simulation platform.Through theoretical analysis and digital simulation,the single-phase LIF(low-impedance-fault)characteristics and HIF characteristics of distribution lines under different grounding modes are compared,and the fault simulation waveform is given,which provides a basis for HIF detection.A HIF identification method for small current grounding system based on zero sequence current nonlinear distortion is proposed.When single-phase HIF occurs in distribution lines,the zero-sequence current waveform is distorted near the "zerocrossing point",and have small linear correlation coefficient between zero-sequence current and time and large distortion.The waveform of the zero-sequence current caused by other reasons is close to a straight line near the "zero-crossing" point,which have large linear correlation coefficient between the zero-sequence current and time and small distortion.Based on the feature of zero sequence current,the identification criterion of high resistance fault is proposed.Aiming at the problem that the zerocrossing deviation caused by the attenuated dc component and waveform distortion of the fault signal leads to the inaccuracy of zero-sequence current distortion detection,a zero-crossing localization method based on the fundamental phase of the signal is proposed,and the implementation steps of HIF identification are given.The correctness and effectiveness of the proposed method are verified by a large number of simulations.A HIF detection scheme for small resistance grounding system based on zero sequence current kurtosis analysis is proposed.The waveform characteristics and kurtosis characteristics of zero sequence current caused by single-phase high-resistance grounding fault are analyzed and compared with the kurtosis characteristics of zero sequence current caused by unbalanced three-phase load and unbalanced three-phase parameters of distribution lines in normal operation.Based on the low kurtosis near the zero sequence current crossing zero of HIF,the kurtosis ratio of one fourth power frequency cycle of zero sequence current and one power frequency cycle is used to detect and select the HIF of distribution lines.The correctness and effectiveness of the method are verified by the simulation results of multiple scenarios.