Study On Dynamic Development Process And Influencing Factors Of Pollution Flashover For Composite Insulators

Composite insulators are widely used in power industry because of their lightweight,strong vibration resistance,high pollution flashover voltage and good economy.However,with the deterioration of the global atmospheric environment,surface pollution is increasing,and power system accidents caused by pollution flashover of composite insulators occur from time to time.After accumulated contamination on the insulator surface,dry bands will form under certain conditions,and local arcs are formed by flashover in the dry bands.These local arcs are bridged to a long arc through the whole insulator surface,and flashover occurs.Therefore,it is of great practical significance to study the formation process and key parameters of arc along the surface under different contamination conditions.In this thesis,based on FZSW-10/4 composite pillar insulators,artificial contamination tests were carried out,and the whole process of local arc formation,bridging and development to surface flashover was recorded.The effects of salt density on corona initiation voltage and flashover voltage of insulators under different contamination levels were compared and analyzed.The test results show that the earliest place where the local arc occurs when the insulator flashovers is the column near the high voltage end metal tool side;according to the test phenomena,the development process of the pollution flashover discharge can be divided into three stages:local arc generation,bridging and surface flashover;the corona initiation voltage and flashover voltage are in accordance with the law of power function with different salt densities,and when the salt density is greater than 0.10mg/cm~2,the effect on corona initiation and flashover voltage is obviously weakened.Based on the basic model of Obenaus'pollution flashover discharge and the theory of gas dynamics(MHD),the dynamic development model of pollution lightning arc for composite insulators is established.The simulation parameters are determined according to the test conditions of artificial pollution.The numerical solution is carried out by using COMSOL multi-physical field coupling module.The distribution changes of temperature field,electric field and current density are calculated and analyzed during the whole process of arc development.The physical causes of the formation of composite insulators from local arc to flashover were obtained.In the process of pollution flashover,the drying effect of current on the insulator along the surface affects the generation of dry bands,resulting in the changes of temperature field and electric field,which interact and correlate with each other,and the distribution of physical quantities is affected by the structure of insulators.In order to study the influencing factors from the formation of local arc to flashover process,the contamination conductivity,the number of dry bands distribution and atmospheric pressure were selected as the research factors for further simulation calculation.The data values of creepage distance along the insulator surface were extracted and the curves were drawn.The simulation results show that conductivity and number of dry bands have significant effects on the development stage of local arc,while atmospheric pressure mainly affects pollution flashover after arc bridging.The results of this paper can explain the causes of the dynamic process of pollution flashover along the surface of composite insulators,and provide a theoretical reference for reducing the probability of pollution flashover of composite insulators.