脱气对525 kV交联聚乙烯绝缘直流电缆空间电荷特性的影响

Effect of Degassing on Space Charge Properties of 525 kV XLPE Insulated DC Cable

为研究脱气对525 kV高压直流交联聚乙烯(XLPE)电缆绝缘中空间电荷分布的影响,分别从脱气和未脱气的XLPE电缆绝缘外、中、内层切取样品,基于电声脉冲法测试了样品内空间电荷的分布情况,并计算了样品内电场畸变率和电荷体密度衰减率。结果表明,电缆绝缘内交联副产物残留量随着脱气时间的增长,由内层向外层依次降低,脱气30 d后,交联副产物残余量基本稳定。当绝缘内层交联副产物α-甲基苯乙烯、苯乙酮、枯基醇的总含量低于3 mg/g,且枯基醇的含量低于2 mg/g时,XLPE电缆脱气充分。空间电荷测量结果显示,XLPE试样内异极性电荷的积聚与交联副产物含量密切相关,异极性空间电荷主要来源于交联副产物的解离,其分布由内层向外层逐渐降低。与未脱气的XLPE试样相比,脱气试样的异极性空间电荷积聚量大幅下降,电场畸变率和电荷密度衰减率明显降低。

To study the effect of degassing on the space charge distribution in the insulation of 525 kV HVDC crosslinked polyethylene(XLPE)cable,sample slices are cut from the outer,middle and inner insulation layers of both the degassed and undegassed XLPE cables.Space charge distributions in the samples are tested based on pulsed electro-acoustic method,the electric field distortion rate and the charge volume density attenuation rate are calculated.The results show that the residual amount of crosslinking byproducts in cable insulations decreases successively from inner to outer layers by degassing time,and the contents of the byproducts keep stable after a 30-day degassing.The degassing process of XLPE cable is considered to be completed when the total content ofα-methylstyrene,acetophenone,and cumyl alcohol in the insulation inner layer is less than 3 mg/g and,at the same time the content of cumyl alcohol is less than 2 mg/g.The results of space charge measurement illustrate that the accumulation of heteropolar charges in XLPE samples is closely related to the content of crosslinking byproducts.The heteropolar space charges are mainly caused by the disintegration of the byproducts,and their distribution decreases gradually from the inner layer to the outer layer.Compared with the undegassed XLPE samples,the heteropolar space charges accumulation of the degassed samples decreases dramatically,and the electric field distortion rate and the charge density attenuation rate are significantly reduced.