Enhanced Breakdown Property Of XLPE With Trace-doping Of Inorganic Nanoparticle And Organic Compound

Power cable is the key equipment of HVDC transmission system.During the operation of the cable,the conductor heating leads to the rise of the insulation temperature,which causes the change of conductivity of insulating material,aggravates the accumulation of space charge and the distortion of local electric field,results in the decline of the breakdown strength,seriously threatening the safe and stable operation of the power system.This thesis focuses on the coordinated regulation of bulk conductivity,space charge and breakdown characteristics of XLPE materials for HVDC cable insulation,proposes the modification method of XLPE based on trace-doping of graphene oxide(GO)nanoparticles and blending of polycyclic aromatic compound(PAC),and reveals the correlation between charge transport behavior and breakdown characteristics of XLPE under DC voltage polarity reversal.The research results are expected to provide theoretical and experimental basis for the development of XLPE insulation for HVDC cable application.The main research work and conclusions are as follows:(1)Inorganic nano-doping modification was used to improve the DC insulation performance of XLPE.By adjusting the mass fraction of GO nanoparticle,it was found that the bulk conductivity and conductivity-temperature coefficient can be significantly reduced,the space charge injection and accumulation can be inhibited,and the breakdown strength can be improved by trace-doping of GO nanoparticles.The quantum well model of XLPE/GO nanocomposite was established by quantum chemical calculation method.The mechanism of GO quantum well controlling charge transport behavior and enhancing breakdown strength was revealed,and the modification method of XLPE insulation based on trace-doping of GO nanoparticles was proposed accordingly.(2)The DC insulation performance of XLPE was improved by organic compounds blending.Through screening different kinds of polycyclic aromatic compounds,PAC molecules which can improve the bulk conductivity and space charge characteristics as well as improve the breakdown strength of XLPE insulation were obtained.The energy band structure and potential distribution of PAC molecule were obtained by quantum chemical calculation.The mechanism of PAC molecule capturing high-energy electrons was revealed.Accordingly,the modification method of XLPE insulation based on PAC molecule blending was proposed.(3)According to the characteristics of space charge and breakdown of XLPE under DC voltage polarity reversal,the law of polarity reversal on promoting space charge accumulation,aggravating local electric field distortion and reducing breakdown strength were obtained.The energy band structure of XLPE/electrode system was analyzed by quantum chemical calculation.The mechanism of polarity reversal on the space charge characteristics of XLPE was revealed,and the correlation between charge transport behavior and breakdown characteristics was established.It was found that GO nanoparticles and PAC molecules have synergistic effect on inhibiting space charge accumulation and improving breakdown strength of XLPE insulation.In view of the above,a modification method of XLPE insulation based on the joint use of GO nanoparticles and PAC molecules was proposed.