Study On The Accumulation And Dissipation Of Surface Charge On Polymer Dielectric Under DC Voltage And Its Effect On Flashover

Insulators play multiple roles such as mechanical support and electrical isolation,and their safe operation is of great significance to the reliability of electrical equipment and even the power system.The free charge will accumulate to form surface charges at the gas-solid interface,so that the flashover characteristics of the insulation under DC voltage show great differences with AC voltage.Therefore,it is of great theoretical significance and practical value to study the accumulation and dissipation of surface charge on polymer dielectric under DC voltage and its effect on flashover.First of all,experiments on the surface charge accumulation characteristics under DC voltage were carried out by means of planar finger-type electrodes for epoxy resin(EP),silicone rubber(SiR),polymethylmethacrylate(PMMA)and polytetrafluoroethylene(PTFE).And the effects of material,voltage action time and voltage amplitude on the surface charge accumulation were analyzed.It is found that the surface charges exhibit bipolar accumulation,that is,positive charges accumulate on the anode side and negative charges accumulate on the cathode side.With the increase of voltage application time,the surface charge accumulation rate gradually slows down and becomes saturated.Second,through the needle-plate electrode corona charging method,the ability of surface charge dissipation of the four materials of EP,SiR,PMMA and PTFE under positive and negative polarity was studied,and then the internal factors that affect the surface charge dissipation was analyzed.The results show that the difference of charge dissipation way of four materials is the main reason for the different charge dissipation rates.Then using planar finger-type electrode,the experimental study on the characteristics of surface charges before and after surface flashover and the influence of surface charge accumulation on the flashover were carried out.Based on the changes of electric field before and after the accumulation of charge,the influence of surface charge accumulation on flashover characteristics was explored.It is found that under this electrode structure,the bipolar charge distribution(accumulation of the same polarity charge on the high voltage electrode side)on the surface of polymer can be used to homogenize the field strength and reduce the field strength of the three bond sites.Finally,considering the influence of solid side conduction,surface conduction and gas conduction on the process of surface charge accumulation,a DC transient field simulation model under air was established.The geometric model corresponding to the experiment was set up to analyze the process and mechanism of surface charge accumulation under the combined action of three ways.On this basis,the influence of relative dielectric constant,bulk conductivity and surface conductivity on the surface charge accumulation and electric field distribution was investigated.The study suggests that the relative dielectric constant and volume conductivity of the insulating material should be properly reduced,and the surface conductivity of the material should be appropriately increased.In this paper,the basic physical process of charge accumulation on the surface and the influence of flashover are explored and analyzed theoretically,which will contribute to further provide the basis and guidance for the modification of insulation medium and insulation optimization.