Dynamic Circuit Model Of DC Flashover On Ice-covered Insulators And Numerical Calculation

With the increasing of EHV and UHV DC transmission lines,the insulators' icing flashover appears more serious.Domestic and foreign scholars have made a systematic study on the ice-covered insulators' DC flashover performance and flashover model,the research helps reduce the DC flashover accidents on ice-covered insulators.While the static model does not reflect the dynamic process of icing flashover,and the existing dynamic flashover models have some limitations on the characterization of arcs.Moreover,there will be multiple arcs developing to flashover during the insulators' icing flashover.Therefore,it is more urgent to study the dynamic circuit model of DC icing flashover.The arc of DC icing flashover contains different types of arc,such as air-gap arc and ice surface arc.Therefore,the dynamic circuit model of single arc and multi-arc DC icing flashover which can distinguish different types of arc is established respectively,and the key circuit elements such as dynamic arc and equivalent residual ice resistance are analyzed and studied.Finally,the model is applied to predict the DC flashover on short insulator strings with severe icing and moderate icing.The main work of this paper and the results obtained are as follows:(1)A single arc equivalent circuit model which can distinguish between the air gap arc and the ice surface arc is constructed,and the dynamic arc resistance model for different types of arc is studied.The influence of ice surface on the arc propagation is taken into account to improve the existing dynamic arc resistance model.On this basis,a new model is proposed,and the arc constants of the ice surface arc is measured by the test.The total calculation formula of the equivalent residual ice resistance which can calculate both the wide band ice layer and the narrow band ice layer is determined,and the numerical law between the equivalent surface conductivity of the ice layer and the conductivity of the ice water is measured by the icing plane experiment.Finally,the numerical formula of each circuit element in the equivalent circuit model is determined.(2)Based on the improvment of the dynamic arc resistance model and the equivalent residual ice resistance calculation formula,an improved dynamic circuit model of single arc DC icing flashover is established.The simulation results of the model are all in a reasonable range,and the validity of the model is verified by compared with the existing dynamic models.The DC icing flashover of severe ice-covered short srting insulators is predicted accurately by this model.Thus,the effectiveness and accuracy of the dynamic circuit model of single arc DC icing flashover which can distinguish between air arc and ice surface arc is proved.(3)On the basis of the study of the dynamic circuit model of single arc DC icing flashover,a multi-arc equivalent circuit model is constructed,which can distinguish between the air-gap arc,ice surface arc made by electrode and ice surface arc made by icecle.The numerical formula of the icecle arc resistance and the equivalent residual ice layer resistance in the multi arc condition is studied and determined.Finally,the DC flashover of the moderate ice-covered short string insulators is predicted accurately by this model.It is proved that the dynamic circuit model of multi-arc DC icing flashover which can distinguish different types of arc predict the ice-covered insulators' DC icing flashover voltage and leakage current waveform accurately,according to the actual icing flashover arc path.The work in this paper provides a theoretical basis for studying the DC icing flashover problem of long string insulators under natural environment,and has a certain engineering value for the icing flashover warning of transmission lines.