| Compared with HVAC transmission,HVDC transmission has the advantages of long transmission distance,large transmission capacity and low line losses,which can meet the future demand of electricity for the social and economic development of China.But under the action of the DC electric field,the space charge is easily accumulated in the insulation,which leads to the distortion of the electric field and even leads to cable insulation breakdown.The semiconductive shielding material is in contact with the insulating layer,which plays the role of the homogenized electric field.In order to improve the problem of space charge in insulation,a shielding material with proper volume resistivity can be used to reduce the injection of space charge in polyethylene.In this dissertation,ethylene vinyl acetate copolymer(EVA)is used as the base resin of semiconductive shielding material.The conductive carbon black(CB)with different content was used as the conductive filler,and the semiconductive shielding material of CB/EVA was prepared by composite.The influence of carbon black content on the volume resistivity of semiconductive shielding materials is studied by experiments.The distribution of space charges in polyethylene is measured by PEA method using semiconductive shielding materials with different volume resistivity as electrodes.The COMSOL Multiphysics simulation software is used to calculate the electric field,which is used to analyze the relationship between the volume resistivity of the semiconductive shielding material and the space charge in the insulation.The experimental results show that with the increase of carbon black content,the volume resistivity of CB/EVA semiconductive shielding material decreases,and finally reaches the percolation threshold when the carbon black content is 32 phr,and the volume resistivity is stable at 9?·cm.The polyethylene average space charge density decreased first and then increased,the content of carbon black is 22 phr,the volume resistivity was 30?·cm,and the average space charge density is minimum.The simulation results show that with the increase of the content of carbon black,the maximum field strength of conductive carbon black particles on the interface between semiconductive shielding layer and insulation layer first decreases and then slowly decreases;when the content of carbon black particles is less than 22 phr,the maximum field strength on the surface is reduced;when the carbon content is greater than 22 phr,the maximum field strength decreased less. |
