Faulty Line Detection And Phase Detection Of Single Phase-to-earth Fault Using Frequency Distribution Theory In Small Current Neutral Grounding System

Small current grounding mode is widely used in medium and low voltage distribution network,mainly including isolated neutral system and resonant grounding system.After single phase-to-ground faults occurred in the system,it is affected by the transition resistance,the fault time and the noise,which makes the effect of the existing line selection method not ideal.In fact,the asymmetry of power grid is ubiquitous,and the situation of single phase grounding fault is complex and changeable.The traditional fault phase selection criterion is difficult to accurately identify the failure phase.Therefore,it is necessary to further study the problem of fault line delection and phase selection.After fault occurred in the system,statistical characteristics of data distribution are significantly different.A novel approach based on frequency distribution theory and correlation analysis was presented to detect the fault line.Firstly,it selects the sampling data of zero-sequence current waveforms in the fist 1/2 cycle after the fault occurred,and extended Prony algorithm is used to extract the power frequency components of each line to determine the range of class interval.Sampling data of zero-sequence current waveforms are split up into several groups by means of frequency distribution theory.After that,frequency distribution values of per line are obtained by Bessel formula,and finally the fault line is selected.For the bus fault,using correlation analysis and frequency distribution theory to determine whether the bus fault occurred.Matlab simulation results and adaptability analysis verify that the proposed method has a high accuracy and strong adaptability.In view of problem of ineffective selection of asymmetric mine neutral point ungrounded system while high resistance grounding occurs,a new method was proposed.Matlab simulation shows that the proposed method has high accuracy and is applicable to fault conditions of low impedance grounding and high impedance grounding.It has strong adaptability to noise interference and data window length,and is not affected by sampling frequency and group distance.