Decision Method For Small Current Neutral Grounding Mode And Fault Line Selection In Distribution Network

In recent years,with the continuous development of the distribution network,its coverage area has increased significantly,and the risk of electric shock to personnel has also risen sharply.The risk of personal electric shock is closely related to the neutral grounding method of the distribution network and the corresponding fault protection technology: in the large current grounding distribution network(mainly means small resistance grounding distribution network),the fault current is large,when a personal electric shock accident caused by the single phase to ground fault occurs,the zero sequence protection of the configuration can shortly cut the fault.In case of a small current grounding system,the fault current is small,when a personal electric shock occurs,the distribution network will operate with a fault for a while,so that personnel may continue to get an electric shock.Therefore,the threat of personal safety caused by the two grounding methods needs to be comprehensively and quantitatively evaluated.Due to various reasons,most of the medium voltage distribution networks in China currently use small current grounding,which requires high economic and time cost if widely reformed.Therefore,under the premise of taking into account the risk of personal electric shock,whether a neutral point should be grounded through a small current method requires careful and scientific quantitative argumentation.At the same time,the existing research lacks the adaptive analysis of the principle of fault line selection.Due to the random selection of the line selection principle in the actual project,the actual installation of the line selection device can not be well adapted to the specific working conditions of the distribution network.When a personal electric shock occurs,the line may not be accurately selected,endangering personal safety.All in all,there is an urgent need for a quantitative decision method for the principle of line selection,to select the most suitable line selection method in combination with the specific working conditions of the distribution network to improve the accuracy of line selection and further ensure personal safety.This paper analyzes the fault characteristics of small current grounding distribution network,calculates the maximum safety distance of personnel against electric shock when single-phase ground fault occurs in distribution network,raises the point that the threat to personnel caused by step voltage is related to both the amplitude of fault current and the duration of fault.Based on the above analysis,an optimization decision method for neutral point grounding of distribution network considering human body electric shock risk is proposed.Firstly,the index sets of personal electric shock risk,over voltage risk and life cycle cost are constructed.And the set of decision-making targets for reliability is proposed;secondly,the minimum degree of inconsistency between each plan and the decision-makers is the optimization goal,so the decision-making problem is transformed into a linear programming problem,and the weight of each target is obtained;then,the weighted Euclidean distance is used for each neutral point grounding method.The grounding scheme is ranked by advantages and disadvantages,and a small current grounding decision method considering personal risk is obtained.On the other hand,for the configuration method of line selection device for small current grounding distribution network,this paper proposes a decision-making model for line selection method,selects the line selection method that is most suitable for distribution network conditions,and improves line selection accuracy,guarantees personal safety.Specifically,the fault characteristics of each line selection principle are firstly simulated and analyzed,and the influenced factors of the line selection principle are proposed.The fault characteristics selection set,the line credibility index set and the related factor set of the distribution network are established,and the correlation model calculation method between the fault line selection credibility index and the related factors is proposed.Specifically,the correlation coefficient between the correlation factor and the line selection credibility index is calculated,and the weight coefficient of the correlation factor to the fault feature is obtained.At the same time,the membership function which can characterize the influence degree of related factors on the credibility index of the line selection is constructed,and the line selection evaluation matrix is formed.The line selection method which is most suitable for the distribution network working condition is selected,which improves the accuracy of line selection and protects the person safety.