Research On Single Phase Grounding Fault Line Selection Of Small Current Grounding System In Distribution Network

The fault of traditional small current grounding system should meet the requirement of power supply reliability and can run for 2 hours with fault.With the development of distribution network automation,the ability to restore negative power supply to load is improved after the fault section is removed;in order to avoid the personal risk caused by the failure of conductor falling to the ground,and improve the impact on personal safety.The new technical guidelines for power grids require: When the fault duration is delayed for 10 seconds,tripping should be performed to isolate the fault locally as soon as possible.This clearly requires that substations should have line selection devices to diagnose and isolate faults.Therefore,this paper studies the fault line selection technology of small current grounding.First of all,this paper summarizes the general situation and development situation of small current fault line selection technology from the aspects of detection principle,accuracy of detection technology,safety,reliability of power supply,and impact on operation and management of power grid.The basic principle of single-phase grounding fault in low current grounding system is analyzed theoretically,the electrical characteristics of single-phase grounding short circuit are briefly described.Secondly,the 10 kV system model of distribution network is built,and the equivalent circuit of equivalent resistance,equivalent inductance and equivalent distributed capacitance is obtained by using the principle of model simplification step by step.The variation rule of fault quantity is analyzed theoretically,and the fault characteristics of single-phase grounding are extracted by combining simulation practice.It provides a theoretical basis for the line selection algorithm of correlation analysis and wavelet analysis.Once again,the simulation analysis shows that zero-sequence and negative-sequence components will appear when single-phase grounding fault occurs in the system.These components do not exist in the normal operation of the power system or exist in the way of unbalanced output.The sensitivity of line selection can be improved by using such fault characteristic components to form line selection protection.Finally,the magnitude,phase and phase angle characteristics of fault components of fault line and sound line after fault are extracted.The correlation between zero sequence current and zero sequence voltage waveforms is studied.The comprehensive correlation coefficients of each line are calculated to form the criterion of correlation analysis for line selection.Multi-resolution analysis of zero sequence current after feeder faults.Calculate the energy coefficients at different scales and compare the weight coefficients.The principle of line selection based on wavelet transform;The influence of neutral grounding mode,grounding resistance and fault initial phase angle on the result of line selection is verified by simulation.The results confirm the validity of correlation analysis and wavelet analysis in line selection.In this paper,a total of 34 pictures,9 tables and 72 references.