Study On Silicone Rubber Nonlinear Composites For HVDC Cable Accessories

Compared with the high voltage AC transmission,the HVDC transmission has the advantages of long transmission distance,large transmission capacity and low line loss,and meets the demand of the future social and economic development of our country.HVDC cable and its accessories as an important part of HVDC transmission,and its research and development is extremely important.Unlike AC cable accessories,the field strength distribution in the insulating structure is inversely proportional to the conductivity of the material volume in DC cable accessories.In order to improve the concentration of electric field near the stress cone,the reinforced insulating material with non-linear conductivity can be used to improve the conductivity of insulating material under high electric field strength,and the maximum field strength in the insulation structure is found in the main insulation of the cable,and make the maximum field strength appears in the cable main insulation.In this paper,silicone rubber composites with conductivity nonlinearity were prepared by adding nano silicon carbide,nano-silica(hydrophilic),nano-carbon black and nano-graphite filler to the silicone rubber matrix.The effects of the types and contents of nanofiller on the DC conductance characteristics,DC breakdown characteristics,dielectric spectroscopy properties and space charge characteristics of the silicone rubber nonlinear composites were investigated experimentally.The internal field distribution of the HVDC cable accessories was analyzed by COMSOL Multiphysics simulation software.The results show that the doping of nano-silicon carbide and nano-carbon black can improve the nonlinearity of the electrical conductivity of the silicone rubber composites with high electric field strength.With the increase of the content of nanofiller,the nonlinearity of the conductivity is more obvious.The addition of nanographite and nano-silica is not obvious for the nonlinear enhancement of the conductivity of the silicone rubber composites.However,under low electric field strength,the conductivity increases with temperature,and the temperature dependence is higher;With the increase of nano-graphite doping content,the strength of the DC breakdown of the silicone rubber composite material decreases faster.The doping of nano-silicon carbide,nano-graphite and nano-carbon black has a great effect on improving the relative permittivity of silicone rubber composites.Appropriate amount of nano-silicon carbide,nano-carbon black/nano-graphite doping can effectively inhibit the accumulation of space charge in the silicone rubber composites;By contrast,5 phr graphite / 3 phr carbon black / silicone rubber composite material as a reinforced insulating material can improve the high voltage DC cable accessories steady state and transient internal electric field distribution.