Comprehensive experiments on the surface flashover characteristics of porous materials under high voltage
[Objective]Gas-solid composite dielectrics are important electrical insulation materials widely used in civil and military high-tech fields,such as electrical/electronic engineering,aerospace,and strong electromagnetic pulse.However,composite insulation is prone to flashover under high electric fields,thus improving the surface flashover strength,which is a key issue in enhancing the overall performance of power equipment.The surface morphology of solid dielectrics has a significant impact on the flashover strength.However,existing surface microstructure tailoring methods are based on the etching approach,which can only construct surface holes or groove-like structures,and the morphology resolution is limited to the micrometer scale.In contrast to etching methods,which only change the surface morphology,this study constructs a three-dimensional foam-like porous structure to effectively enhance the surface flashover voltage.[Methods]Polydimethylsiloxane(PDMS)was selected as the matrix material to prepare bulk porous materials via the oil/water emulsion method.Deionized water was dispersed into PDMS by electrical stirring,and the PDMS and water droplets formed the oil/water emulsion.Afterward,PDMS was cross-linked and solidified by heating to form a porous structure with high mechanical strength.Three different mass ratios of deionized water to PDMS,namely 10％,30％,and 50％,were considered in the experiments.A comprehensive experimental system was established to characterize the surface flashover characteristics of porous insulation materials under high voltage.The flashover strength in different gas atmospheres was tested in a closed gas discharge experimental chamber,and the initiation and development processes of surface discharge were analyzed through optoelectronic joint diagnosis.The isothermal surface potential decay method was employed to measure the trap energy distribution and explore the influence of porous structure on charge dissipation rate and trap distribution.A fluid simulation model for surface streamer propagation on porous solid dielectrics was built to analyze the influence of pores on the development process of surface discharge.[Results]Results showed that,with the increase in deionized water content,the pore size and porosity of porous PDMS gradually increased.Increasing the porosity and pore size can also effectively improve the hydrophobic performance.The porous structure effectively enhanced the surface flashover voltage,and the flashover strength increased with the porosity.The maximum increment in direct current flashover voltage was 53％.The surface potential scanning and streamer simulation results showed that the porous structure can effectively hinder the collision ionization process,thereby suppressing microdischarges.The measurement results of surface potential decay indicated that the mobility of charges in pores is higher than that on the surface of solid dielectrics.Therefore,the porous structure plays a role in promoting the dissipation of surface charges,which is enhanced with the increase in porosity.[Conclusions]The effects of hindering collision ionization and promoting surface charge dissipation by porous structures are beneficial for enhancing the surface flashover strength,and both effects are enhanced with the increase in porosity,resulting in an improvement in flashover strength with the increase in porosity.This experiment involves electrical engineering,materials,physics,and multiphysics field simulations,which can effectively improve students'comprehensive abilities in experimentation,simulation,and theoretical analysis.
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