Line Identification Method Of High-resistance Grounding Fault In 10kV Flexible Grounding And Small Resistance Grounding System

Distribution network directly distributes electric energy to end users.Its neutral grounding mode is of great significance to ensure the power supply reliability.Neutral grounding through arc suppression coil is widely used for its effectively extinguishing the arc and preventing overvoltage.But this grounding method also has the problem of poor line selection accuracy.The flexible grounding mode of parallel small resistance of arc suppression coil has the function of fault arc suppression and fault line identification.With the development of distribution network and the increasing proportion of cable,some important power users put forward higher requirements for rapid fault removal,so the small resistance grounding mode is gradually popularized and applied.However,at present,most distribution networks under these two grounding modes adopt definite time zero sequence overcurrent protection,which has the problem of insufficient sensitivity to distinguish the fault line in case of high-resistance grounding fault.Therefore,the research on the fault line identification method of flexible grounding and small resistance grounding system to adapt to high-resistance grounding fault has important theoretical and practical significance.Firstly,this paper analyzes and compares the characteristics of different neutral grounding modes,highlights the advantages of flexible grounding mode and small resistance grounding mode,and discusses the factors affecting the selection of neutral grounding mode in distribution network.Secondly,the characteristics of zero sequence voltage and current before and after the input of small resistance are studied when there is a fault in 10 kV flexible grounding system,and a fault line identification method based on the change of phase difference of the zero sequence current and voltage is proposed.Considering the insufficient measurement accuracy of zero sequence voltage transformer after the input of small resistance,a method of calculating the approximate zero sequence voltage phase by using the bus voltage phase before the fault is added.The proposed method is not affected by the grounding resistance in theory.It can judge whether the line is fault only by using the line zero sequence current and voltage.PSCAD simulation shows that the proposed method has strong ability to withstand high resistance grounding fault.Finally,the characteristics of zero sequence voltage and current in single-phase grounding fault of 10 kV small resistance grounding system are analyzed,and a fault line identification method based on the ratio coefficient of zero sequence current(the ratio of line zero sequence current to neutral zero sequence current)is proposed.In principle,the method can eliminate the influence of grounding resistance and take the influence of unbalanced current into consideration.Theoretical analysis and simulation results show that this method has the advantages of simplicity,reliability and strong resistance to ground resistance.In this paper,the single-phase grounding fault characteristics of 10 kV flexible grounding system and small resistance grounding system are studied.The proposed fault line identification method effectively improves the sensitivity of fault line identification in case of high resistance grounding fault,and is of great significance to quickly remove the fault and ensure the reliability of power supply.