Surface charges greatly affect the discharge/flashover development process across an insulator.The relationship between surface charge distribution on insulating materials and measurement data based on Pockels technique is discussed,and an improved algorithm is built to calculate the real surface charge density from original data.In this algorithm,two-dimensional Fourier transform technique and Wiener filter are employed to reduce the amount of numerical calculation and improve the stability of computation.Moreover,this algorithm considers not only the influence of sample’s thickness and permittivity,but also the impact of charges at different positions.The achievement of this calibration algorithm is demonstrated in details.Compared with traditional algorithms,the improved one supplies a better solution in the calibration of surface charge distribution on different samples with different thickness.
For pulsed power devices,surface flashover phenomena across solid insulators greatly restrict their overall performance.In recent decades,much attention has been paid on enhancing the surface electric withstanding strength of insulators,and it is found that surface treatment of material is useful to improve the surface flashover voltage.The carburization treatment is employed to modify the surface components of newly-developed machinable ceramics(MC) materials. A series of MC samples with different glucose solution concentration(0%,10%,20%,30% and 40%) are prepared by chemical reactions for surface carburization modification,and their surface flashover characteristics are investigated under pulsed voltage in vacuum.It is found that the surface carburization treatment greatly modifies the surface resistivity of MCs and hence the flashover behaviors.Based on the reduction of surface resistivity and the secondary electron emission avalanche(SEEA) theory,the adjustment of flashover withstanding ability can be reasonably explained.
Improvement of polytetrafluoroethylene surface energy by non-thermal plasma treatmentis presented,using a nanosecond-positive-edge repetitive pulsed dielectric barrier dischargegenerator in atmospheric air.The electrical parameters including discharging power,peak anddensity of micro-discharge current were calculated,and the electron energy was estimated.Surfacetreatment experiments of polytetrafluoroethylene films were conducted for both differentapplied voltages and different treating durations.Results show that the surface energy of polytetrafluoroethylenefilm could be improved to 40 mJ/m^2 or more by plasma treatment.Surfaceroughness measurement and surface X-ray photoelectron spectroscopy analysis indicate that thereare chemical etching and implantation of polar oxygen groups in the sample surface treating process,resulting in the improvement of the sample surface energy.Compared with an AC sourceof 50 Hz,the dielectric barrier discharges generated by a repetitive pulsed source could providehigher peak power,lower mean power,larger micro-discharge current density and higher electronenergy.Therefore,with the same applied peak voltage and treating duration,the improvementof polytetrafluoroethylene surface energy using repetitive pulsed plasma is more effective,and theplasma treatment process based on repetitive pulsed dielectric barrier discharges in air is thusfeasible and applicable.
