Research On Single-phase Ground Fault Line Selection Method For Small Current Grounding System

Small current grounding system is widely used in the distribution network.Single-phase ground fault probability is as high as 80%.Though it can continue to run 1-2 hours,if the fault is not promptly removed,not only will cause damage to the equipment,but also causing significant electrical accident.Therefore,it is helpful for the safe and stable operation of power system to accurately and quickly determine the fault line and fault phase.In this paper,the method of fault line and phase selection of single-phase grounding in small current grounding system is studied.The main research contents are as follows:The characteristics of single-phase grounding fault in small current grounding system are analyzed.The correlation between zero-sequence signal line selection method is studied.In order to solve the problem that the similarity of the zero-sequence component in the whole frequency band is weak,the characteristic frequency band is determined by the phase-frequency characteristic of zero-sequence impedance.The results show that the similarity of zero-sequence component is better under the characteristic frequency band.To solove the problem that the correlation coefficient method has poor anti-interference ability of fault line selection when there is all kinds of interference in real grid sampling signal,the cross correlation function method is applied to fault line selection to improve the anti-interference ability.And this method is verified accurate and universal under different fault conditions.The application of injecting signal method and phase current difference method in fault phase selection is studied.In this paper,these two methods are used together.Using injection signal solves the problem that the sensitivity of the variation of phase current differential method is weak when the current is light.The best injection signal is determined from the number of phases of the injected signal,the fault phase,the AC signal phase,the AC signal frequency and the transition resistance.This paper analyzes and summarizes the influence factors of the phase selection after the injection signal and verifies the method under different fault conditions.The results show that the phase selection results of the improved variation of phase current difference method with stronger applicability.