Space Charge And Electric Conductivity Of Nano-Metal Oxides/LDPE Composite

In high voltage DC transmission lines, polyethylene becomes the choicematerials of DC cable insulation, because of its excellent physical properties andelectrical insulation performance and environment friendly, However, whenpolyethylene is the insulation of high voltage direct cables, there will be a largenumber of local traps in insulation layer. These traps can result in internal spacecharge accumulation, so as to make the distortion of insulating internal electric field;anther characteristic is high temperature coefficient of polyethylene insulationresistance. When the DC cable is running under full load, the resistivity of thepolyethylene will present the exponential distribution with temperature changing,which will cause the distortion of internal electric field in insulating layer.Nanocomposite can effectively suppress space charge injection, and improveinsulating resistance‘s temperature characteristics of the material. The purpose of thisdissertation is studying the space charge properties and conductivity characteristicsof nanocomposite used as DC cable’s insulating materials.The dissertation pays attention on the inhibition effect of space charge ofdifferent preparation methods for nanocomposite. Solution methods, internal meltingblend method and mill melting blend method are used for preparing nanocomposite.Three kinds of samples are used for space charge test. Through PEA test’s result, thebest of preparation method of nanocomposite which can effective suppress spacecharge capacity is selected.The dissertation discusses the conductivity of three nanocomposite. Nano-MgO,nano-SiO₂, nano-TiO₂three nanoparticles are used as fillers, and the paper adoptsmill melting blend method to prepare nano-metal oxide/LDPE composites. Thesamples are divided into two groups: one group is prepared for space-charge-limited-current testing, and I-t curves and I-V curves analyzing of four kinds of nanocomposite. At the same time, the test results are compared with space chargetesting results. Another group is surveyed in I-T curves under different electric fields,then the dissertation analyzes conductivity-temperature characteristics of four kindsof materials.According to the internal electric field distribution formula of DC cableinsulation layer, the dissertation simulates LDPE and nano-SiO₂/LDPE’s electricfield distribution when two kinds of insulation materials are used to DC cableinsulation. The simulation results show that the nano-SiO₂/LDPE as dc cableinsulation can improve with the electric field distribution rule with temperaturechanging.