Study On Structure And Properties Of HVDC Nanocomposite Dielectric System

Cross-linked polyethylene?XLPE?insulation material has been used in cable manufacturing for several decades.It has shown good electrical properties,high and low temperature resistance,aging resistance and so on in the process of AC high-voltage power transmission.However,the characteristics of the cable in the DC transmission,especially the relationship between the conductance coefficient and the temperature of the insulating material,the space charge in the insulation,and other issues have limited its development.While nanocomposite technology opens up a new field for obtaining high performance insulating materials.In this paper,different surface modifiers KH550,KH560 and A-151 were used to modify the surface of nano-Si O₂,respectively,and the composite dielectrics of different content of nano-Si O₂ were prepared by melt blending.The dispersion state of organic nano-Si O₂ in the nanocomposite dielectric matrix,the microstructure of the nanocomposite dielectric,and its influence on physical and mechanical properties and dielectric properties were studied.Scanning electron microscopy?SEM?was used to analyze the dispersion and distribution of nanoparticles modified with different surface modifiers in the XLPE matrix,when the content of modified nano-Si O₂ was 2%,indicating that the organic nano-Si O₂ with a mass fraction of 2%achieved a good dispersion effect in the composite dielectric.Differential scanning calorimetry?DSC?was used to analyze the melting and crystallization behavior of the composites,and the crystalline morphology and distribution of the samples after corrosion were observed by microscope,indicating that the heterogeneous nucleation of organic nano-Si O₂accelerates the crystallization rate of the polymer,decreases the melting point,reduces the crystal size,and makes the crystal distribution more uniform.The tensile strength and elongation at break of the composite dielectric were tested by mechanical tests.When the content was low,a strong interface force was formed between the organic nanometer Si O₂ and the dielectric matrix,and the nanoparticles played the role of physical crosslinking point,which significantly improves the mechanical properties of the composite dielectric;With the increase of the content,the interface binding force decreases,and too many Si O₂ nanoparticles become the stress concentration point,which leads to the weakening of mechanical properties.Through the analysis of the dielectric properties of composites such as dielectric constant,dielectric loss tangent,volume conductivity and breakdown field strength,the results show that:At a certain content,the action of anchoring and steric hindrance of the organic nano-Si O₂ restricts the movement of the molecular chain in the interface region,and under the synergistic action of the interfacial forces,dipoles are difficult to turn and the polarizability is reduced,the relative dielectric constant and the dielectric loss decreases;A strong interfacial force is formed between the organic nanoparticles and the polymer matrix,and a large number of deep traps are formed at the interface,which limits the movement of the carriers and reduces the conductivity of the composite dielectric;With the addition of organic nano-Si O₂,the particles dispersed more uniformly in the XLPE matrix,the microscopic defects were reduced,and the breakdown field strength was significantly improved.The test of the breakdown field strength of the specimens with different thickness shows that with the increase of the specimen thickness,the defect probability increases and the breakdown field strength decreases.The space charge characteristics of nanocomposites are measured by pulse electro-acoustic method?PEA?.The results indicate that the interfacial effects of organic nano-Si O₂ introduce deep traps in the polymer matrix,which are beneficial to bound charge and reduce the carrier mobility,thus effectively avoiding the accumulation and migration of space charges.The effect of organic surface modifier on the space charge transfer and suppression characteristics of nanocomposites is discussed based on the structural characteristics.