Preparation And Electrical Properties Of Polyethylene Composites Doped With Fast Ionic Conductors

As an important part of high-voltage DC?HVDC?transmission cable,semi-conductive layer can prevent the local electric field distortion of the insulation layer under the action of HVDC electric field,and it can make the conductor core and the insulation layer closely connected,reduce the air gap between the conductor and the insulation layer,.At the same time,the semi-conductive shielding layer can reduce the temperature rise of the insulation layer to a certain extent and protect the main insulation layer,so the performance of the semi-conductive shielding layer for HVDC cable is very important for the use of HVDC cable.However,during the operation of the cable,the resistivity of the semi-conductiveshielding layer will increase with the increase of temperature,and it will suddenly increase at 90?,representing a significant positive temperature coefficient effect?PTC effect?,.It will cause the cable to heat up and cause the interface to melt partially.Therefore,suppressing the PTC effect of the semi-conductive shielding materials has an important impact on the use of high-voltage DC cables.In this paper,composite materials of conductive carbon black?CB?,low density polyethylene?LDPE?and ethylene vinyl acetate copolymer?EVA?is prepared by a double-roll mill,and the composite materials were used as a masterbatch for high-voltage DC cable semi-conductive material.The LSC/CB/LDPE/EVA composite semi-conductive materials and LLC/CB/LDPE/EVA composite semi-conductive materials were prepared by adding La_0.6Sr_0.4CoO₃?LSC?and La₂Li_0.5Co_0.5O₄?LLC?into the master batch respectively.The PTC effect of the semi-conductive shielding materials is suppressed due to the increase in the conductivity of the ionic conductor with increasing temperature.At the same time,the ability of modified semi-conductiveshielding materials to inhibit space charge injection was tested by pulsed electro-acoustic?PEA?method and thermally stimulated current?TSC?method.1.The fast ionic conductor La_0.6Sr_0.4CoO₃?LSC?was prepared by the Glycine-nitrate combustion process?GNP?method and the sol-gel method,and the X-ray diffraction characterization of the LSC prepared at different pH values was performed.The morphology of LSC was characterized by SEM,and the crystallinity,purity and morphology of LSC powder prepared by the two methods were compared.The influence of pH value on LSC powder was also explored.The results show that the purity of LSC is higher when the sol-gel method is used and the pH of the precursor solution is 9-10.La₂Li_0.5Co_0.5O₄?LLC?was prepared by sol-gel method,and the prepared LSC and LLC were ball milled at different times.Field emission scanning electron microscopy tests show that the LSC and LLC particles are smaller and more uniform in size after ball milling,and the agglomeration between particles is also reduced.2.The prepared fast ionic conductors LSC were added to the CB/LDPE/EVA composite material using an internal mixer to obtain semi-conductive shielding materials of the LSC/CB/LDPE/EVA system.The resistivity of the composite materials was tested with a semi-conductive rubber-plastic resistivity tester.The results show that the addition of LSC can significantly weaken the PTC effect of the semi-conductive shielding materials.The shielding performance of the composite materials was characterized by the pulsed electro-acoustic?PEA?and the thermally stimulated current method?TSC?.The test results show that the LSC/CB/LDPE/EVA semi-conductive shielding layer has good space charge suppression ability.The addition of 1%has the best effect in suppressing space charge injection.3.The LLC/CB/LDPE/EVA system semi-conductive shielding materials were prepared by adding LLC to the masterbatch through an internal mixer.The resistivity test results show that when the added amount of LLC is 0.5%,it can obviously inhibit the PTC effect of the semi-conductive shielding materials.The PEA and TSC tests show that at this doping level,the ability of the semi-conductive shielding materials to suppress space charge injection is also very good.At the same time,the charge emission characteristics of the semi-conductive materials were studied by using the SIM?semiconductor electrode-insulating material-metal lower electrode?electrode structure,and it was found that LLC doping can reduce the charge emission of the semi-conductive electrode to the insulating layer.