Research On Lightning Overvoltage Analysis And Protective Measures Of Distribution Transformer

In recent years,with the rapid development of economy and urban construction,social power consumption has increased significantly,and the distribution network has continued to grow and develop.As the most important equipment in the distribution network,the safe and stable operation of distribution transformers is directly related to thousands of households.Ten thousand households use electricity.Distribution transformers are widely distributed in regions.Many distribution transformers are located in high-frequency areas where thunderstorms occur.They are more prone to accidents that damage the distribution transformers due to lightning strikes,causing power supply interruptions and even threatening personal safety.Therefore,further research on distribution transformers The lightning protection performance of electric transformers,and effective lightning protection measures are of great significance to the development of the distribution network and the development of society and economy.This paper studies the lightning overvoltage situation and protective measures of distribution transformers.First,establish broadband equivalent models of distribution transformers according to the different wiring groups,use formula calculation methods to obtain stray capacitance parameters,and verify the model’s performance through experiments.Validity;then,according to the established simulation model,the electromagnetic transient program ATP-EMTP is used to analyze the overvoltage of the distribution transformer for direct lightning strikes and induced lightning,and formulate the three-phase three-column distribution transformer and the three-phase five-column distribution transformer The difference in overvoltage transmission of distribution transformers,quantitative analysis of the difference in lightning protection performance of distribution transformers of Dyn11 and Yyn0 wiring groups,and qualitative simulation verification by Ansoft Maxwell;finally,in response to the urgent need to improve the lightning protection performance of distribution transformers,On the basis of insulation coordination analysis and electric field simulation calculation,a new type of solid-sealed insulation lightning protection sleeve for distribution transformers is proposed to limit lightning overvoltage in depth,and its structure and insulation parameters are analyzed,and its failure probability is explained.The calculation method of the finite element software COMSOL Multiphysics was used to simulate and compare the effects of the height and cross-sectional area of the zinc oxide valve plate of the lightning protection sleeve on the failure probability,lightning absorption capacity and residual pressure.The effect on the valve plate of the lightning protection sleeve The dimensional structure proposes optimization suggestions,and finally quantitatively explains the protective effect of the lightning protection sleeve.The research in this paper shows that the zero sequence excitation reactance of the three-phase five-column distribution transformer is larger than that of the three-phase three-column distribution transformer,and the lightning protection performance is better;in terms of wiring group,Dyn11 wiring power distribution The transformer,because the high-voltage side adopts delta wiring,so the lightning current can circulate in the closed loop of the delta-connected high-voltage winding,the total magnetic potential of the lightning current on each iron core leg is almost zero,eliminating the positive and inverse transformation overvoltage,So Dyn11 distribution transformer has better lightning protection performance.Through the analysis of the structure of the solid-sealed insulation lightning protection sleeve,the results show that increasing the cross-sectional area or height of the zinc oxide valve plate can reduce the failure probability,while increasing the cross-sectional area of the zinc oxide resistance core in the lightning protection sleeve will reduce the zinc oxide The lightning absorption energy of the valve plate itself,but the residual voltage of the zinc oxide resistance core will decrease;and increasing the height of the zinc oxide resistance core will increase the absorption energy of the zinc oxide resistance core,but the residual voltage of the zinc oxide resistance core will increase.Finally,the lightning protection effect of the lightning protection bushing is calculated,and it is confirmed that the solid-sealed insulation lightning protection bushing has the dual functions of a lightning arrester and a bushing of the distribution transformer winding,which can deeply limit the lightning overvoltage and maintain the external insulation of the transformer.