| Polyethylene has been widely applied in the insulation materials of transmission and distribution cables due to its excellent electrical,mechanical and physical and chemical properties.With the development of modern power system,the load and voltage level of cables will be higher.Compared with traditional polymer/inorganic micro composite system,polymer/inorganic nanocomposites exhibit higher dielectric strength and better partial discharge resistance.However,the composite with micrometer packing shows better heat conduction effect.Therefore,the effect of its surface corrosion resistance is more prominent.How to combine the performance advantages of the two and develop the application performance of the composite material in a deeper level.In this paper,low density polyethylene（LDPE）were used as matrix materials,30 nm,60nm and 100 nm SiO2 as the inorganic filler by two step melt blending method,were prepared with different particle size and different concentration of SiO2/LDPE nano composite materials,nano composite materials obtained by one-step melt blending with SiO2 once again made by melt blending with different particle size of micro nano SiO2/LDPE composite materials.Scanning electron microscopy（SEM）was used to observe the dispersion degree of nanoparticles in the composites.When nanoparticles were filled with low concentration,they could be dispersed uniformly in the polymer matrix.When the filling concentration reached 5wt%,the nanoparticles would be agglomerated.Using polarized electron microscopy（PLM）and differential scanning calorimetry（DSC）analysis of the process of crystallization and crystallization of composite materials,found that nano SiO2 particles makes LDPE crystal size,crystal structure change,improve the crystallinity of the composite material,the concentration of 3wt% filled.The pure LDPE,SiO2/LDPE nano composite and micro nano SiO2/LDPE composite AC breakdown tests and DC breakdown tests,the results show that the inorganic particles filled with the same size,concentration of 3wt%,nano composite material the highest breakdown strength of inorganic particle filled 30 nm SiO2/LDPE composites with the same concentration,the highest breakdown strength.For the micro nano composite materials,with 30 nm SiO2/LDPE composite material as the base of the micro nano composite material the highest breakdown strength and shape parameter of Weibull micro nano composite material is higher than that of composite and pure LDPE,show that adding micron SiO2 dispersed in the matrix in nano SiO2.Through dielectric spectrum test,it can be found that SiO2 with different particle size and different filling concentration has different effects on the dielectric constant of composites.By thermally stimulated current test（TSC）,it is found that the addition of nanoparticles can change the energy level and density of shallow traps in polymer matrix,and introduce deep traps.The larger the concentration of inorganic particles,the greater the density of shallow traps. |
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