Study On Dielectric Properties Of Nano-SiC Modified Epoxy Composite

In recent years,HVDC transmission technology has been widely used in large-capacity,long-distance transmission systems due to its advantages of large transmission capacity,low loss,and good economy.With the continuous development of high-voltage DC transmission technology,the line voltage level continues to increase,and a large amount of surface charge is likely to accumulate on the surface of the composite insulator under the long-term effect of a strong DC electric field.The accumulation of surface charge causes distortion of the electric field on the surface of the insulator,resulting in a reduction in the flashover voltage along the surface of the insulator.Surface charge accumulation and surface flashover faults have become bottlenecks that limit the further development of HVDC transmission technology.In order to solve the problem of charge accumulation on the surface of epoxy composite insulators,E51 epoxy resin was used as the matrix,methylhexah-ydrophthalic anhydride as the curing agent,DMP-30 as the accelerator,Al₂O₃ as the main filler,and nano-SiC as the modified filler.Five sets of composite material samples with SiC mass fractions of 0wt%,0.5wt%,1.5wt%,2.5wt%and 3.5wt%,respectively.In this paper,a dielectric performance test platform,an isothermal surface potential attenuation test platform and a surface flashover test platform were built in the laboratory,and the relevant composite materials were modified at four temperature points of 25?,40?,60?and 80?.The performance parameters were tested experimentally.The results of the dielectric properties study show that the volume conductivity,relative dielectric constant and dielectric loss factor of the composites increase with the increase of SiC doping concentration,and the DC breakdown field strength decreases with the increase of doping concentration.When the doping concentration of SiC is 2.5wt%and 3.5wt%,the volume conductivity of the sample is obviously nonlinear with the increase of the electric field strength.With increasing temperature,the volume conductivity,relative permittivity and loss factor of the composite material generally showed an upward trend.When the doping concentration of SiC is0wt%,0.5wt%and 1.5wt%,the DC breakdown field strength of the composite decreases with increasing temperature.When the doping concentration is 2.5wt%and3.5wt%,the DC breakdown field strength with the increase of temperature,the trend of decreasing first and then increasing.The results of surface potential decay and flashover along the surface indicate that the increase of nano-SiC doping concentration and temperature both promote the dissipation of surface charge.The higher concentration of SiC doping introduces a lot of shallow traps inside the composite material,which suppresses the build up.The surface flashover voltage of the composite decreases first and then increases with the increase of SiC doping concentration.The surface flashover voltage of 2.5wt%and3.5wt%samples is higher than that of undoped samples.The surface flashover voltage of the material and the surface flashover voltage of the composite material decrease with increasing temperature.