Surface Charge Accumulation And Suppression Of Epoxy Resin Regarding HVDC GIS Spacer

HVDC gas insulated switchgear(GIS)is one of the important power equipments in HVDC system.Charges accumulate on surface of disc-type spacers under different kinds of complex electric field environments,which leads to insulation breakdown easily.The dynamic characteristics of surface charge under combined DC and pulse voltage are researched in this paper.The molecular structure modification of sample surface and doping of nonlinear particles in the sample are used to improve insulation performance.The inhibition mechanism of charge accumulation on the surface of insulation material is revealed.This dissertation provides the theory and experiment evidence for the development of HVDC insulation property.The main research work and achievements are as follows:(1)The dynamic characteristics of surface charge under DC and pulse voltage are researched.If DC and the same polarity pulse voltages are applied,the absolute value of the initial surface potential decreases at first and then increases with the rise of pulse voltage amplitude.The speed of surface charge dissipation has the same tendency.If DC and the heteropolar pulse voltages are applied,the polarity of the surface potential of the sample center changes with the increase in pulse amplitude.In this case,the surface potential will decrease from the opposite polarity to zero.After that,it becomes original polarity potential and then increases.It shows that the pulse voltage can change the surface electric field distribution and the trap energy distribution.(2)By studying the surface charge accumulation and dissipation characteristics of fluorinated sample under DC and pulse voltage,it is found that the replacement of H atoms by F atoms forms a micron-thickness C-F layer on the surface of epoxy resin.Under the same corona voltage,the fluorinated sample has a smaller initial surface charge density and higher dissipation rate.The reverse electric field formed by the bound charge in fluorinated layer weakens the carrier injection.The fluorinated layer shields deep traps in the material,thereby suppressing the surface charge accumulation and uniforming the surface electric field distribution.Moreover,the fluorination treatment improves the flashover voltage of epoxy resin.(3)By studying the bulk conductivity,surface charge and flashover voltage of SiC/epoxy resin non-linear conductive composites,it is found that the composites with higher SiC content exhibit non-linear conductivity under high electric field.With the increasing of SiC content and the applied DC electric field,the increment of surface potential decreases obviously and the surface potential decay rate increases.The carriers in the SiC/epoxy composites with high SiC content overcome the interface barrier by the thermal transition or tunneling effect under high field strength,which accelerates the mobility of carriers.It reduces the accumulation of surface charge under the high electric field and thus restraining the flashover.