Dielectric Properties And Space Charge Characteristic Study Of Liquid Silicone Rubber Modified By Nano-TiO₂

The high voltage direct current cable accessory is an essential part of HVDC transmission,and the distortion of electric field distribution often happens due to its the complex structure and compact size,which can cause insulation breakdown and power supply accident.In order to solve the problem of uneven distribution of electric field caused by the accumulation of space charge and conductivity differences between cross-linked polyethylene(XLPE)and liquid silicone rubber(LSR)in the DC cable accessories,the new nano-composite silicone rubber material was developed to realize the conductivity matching between the LSR and XLPE,and also to inhibit the accumulation of space charge under different temperatures and DC electric field strength,which ensures the uniform distribution of electric field in LSR.In this thesis,the liquid silicone rubber with the two components used as the substrate and nano TiO2 used as modified filler,the TiO2/LSR composite with different nano TiO2 contents was made,and the micromorphology of the composite material was observed by scanning electron microscopy(SEM)to investigate the distribution and dispersion of the nanoparticles in the composite silicone rubber.The dielectric property and breakdown characters of TiO2/LSR were measured in the laboratory,and the influence rules of temperature and electric field strength on their dielectric property.The experiment results show that the conductivity of LSR can be enhanced by adding nano TiO2,and the conductivity increases with the increase of temperature and electric field strength,at the 4% to 6% content of nano TiO2,the conductivity of TiO2/LSR can match the conductivity of XLPE under different temperature and electric field strength;the dielectric constant and loss factor tend to increase with the increase of content of TiO2,and the breakdown voltage tends to decrease with increase of temperature and the content of TiO2.In order to study the influence of nano TiO2 addition on characteristics of space charge accumulation,the distribution of space charges was measured by electro acoustic pulse method in this thesis,the experiment results show that a lot of homopolar charge accumulates near the electrodes in the pure silicone rubber under DC electric field,the homopolar space charges can be inhibited after adding nano TiO2 to the pure silicone rubber,and the amount of space charge accumulation in TiO2/LSR composite material can reach the minimum at the nano TiO2 content from 4% to 6%.