Research On DC Dielectric Properties Of LDPE/Micro-Nano ZnO Composites

There is an increasing demand on insulation level in transmission part of grid with the development of modern electrical system.Polymer which is modified by inorganic nano-fillers can enhance its insulation level effectively.However,nano-particle is easily concentrated and then will lose its excellent properties due to the small particle size and high surface energy in the process of preparation,storage,transportation and using.On another hand,the fillers in micro size exhibit excellent performance on corona resistance and thermal properties.So if the composite contains both micro and nano filler,the various microstructure of composite can be obtained by adjusting the ratio of micro and nano filler and filling order etc.,and the dielectric properties of micro and nanocomposites could surpass that of the composites which the filler content is equal to the former composites but the species of filler is single.Low density polyethylene(LDPE)is chooses as matrix,micro-Zn O and nano-Zn O are respectively as filler in this thesis.Composites in different filler contents and manufacture process are prepared by multistep melt-blend method.The Fourier transform infrared spectroscopy(FTIR),the scanning electric microscope(SEM)and the polarizing microscope(PLM)are used to analyze the micro structure of various composites.The conductivity,breakdown strength,space charge distribution of composites are tested and analyzed.The impact on dielectric properties from the existence of fillers is studied.The test results show that aggregation phenomenon is reduced obviously in nano-Zno which is organized by KH570,there is great dispersion in all composites with micro,nano Zn O particles,moreover,the function of filler in matrix is heterogeneous nucleation which can lower crystallization scale and homogenize the crystallization shape,and then make the structure more compact.In the respect of dielectric performance,micro-nano composites have superior properties of suppressing the space charge accumulation and reducing shortcircuit residual charge than LDPE and other two materials which contains only micro Zn O or nano Zn O.The conductivity of micro-nano composites is roughly equal to LDPE under different field,but better than micro-composites and inferior to nano-composites.The DC breakdown strength of micro-nano composites is 6% higher than LDPE,and that of nano composites is 15% higher.And then comparative analysis is conducted for dielectric properties of the composite materials in the same content of micro/nano Zn O but in different preparation technology,the results show that the composite material being used of nano composite materials as master batch is superior to other three kinds composite materials prepared by means of the different process technology in the inhibiting the space charge accumulation and reducing short-circuit residual charge.