纳米炭黑/XLPE复合绝缘热老化特性试验研究

Study on Thermal Aging Properties of Nano-CB/XLPE Composite Insulating Materials

采用纳米炭黑对交联聚乙烯进行纳米改性是制备低活化能、高电场依赖性高压直流电缆绝缘材料的一种可能技术途径,纳米炭黑/交联聚乙烯(nano-CB/XLPE)复合材料的热老化性能是关系到高压直流电缆长期运行可靠性的关键因素之一。为此,对nano-CB/XLPE复合材料进行加速热老化,研究老化时间对其电导率与介电参数的影响规律。为了表征复合材料的老化程度采用傅里叶红外光谱观察了老化过程材料内部特征官能团变化,并使用扫描电子显微镜(SEM)和差示扫描量热分析仪(DSC)探究了老化过程中材料微观结构变化。试验结果表明,nano-CB/XLPE复合材料随老化时间可分为两个老化阶段,在老化初始阶段,试样的羰基指数增长缓慢,结晶度较大,电导率随老化时间增加而减小,电导活化能随老化时间增加而增大,电场依赖系数变化较小,介电常数和介质损耗因数基本不变;在老化后期,试样的羰基指数增长迅速,结晶度减小,电导率随老化时间增加而增大,电导活化能和电场依赖系数降低,介电常数和介质损耗因数随老化时间增加而增大。

Adopting nano-carbon black to cross-linked polyethylene is a possible technical approach to prepare insulation materials for HVDC cables with low activation energy and high electric field dependence coefficient.And the thermal aging performance of composites combined with the nano-carbon black and the cross-linked polyethylene(nano-CB/XLPE)is one of critical factors which are related to the long-term operation reliability of the HVDC Cable.Therefore,the regularity about the effect of aging time on the conductivity and dielectric constant is studied,by accelerating heat the nano-CB/XLPE composites.In order to characterize the aging degree of composites,the changes of internal characteristic functional groups in the aging process are observed by using the Fourier transform infrared spectroscopy(FTIR),and the microstructure changes of composites during aging are investigated by using the scanning electron microscope(SEM)and differential scanning calorimeter(DSC).The experimental results show that nano-CB/XLPE composites can be divided into two aging stages with aging time.In the initial stage of aging,the carbonyl index of the sample increases slowly,the crystallinity is large,and the conductivity decreases with the increase of aging time,while the activation energy of conductivity increases with the increase of aging time.At the same time,the electric field dependence coefficient changes little,and the dielectric constant and dielectric loss factor are basically unchanged.However,in the later stage of aging,the carbonyl index of the sample increases rapidly,the crystallinity decreases,the conductivity increases with the increase of aging time,the activation energy of the conductivity as well as the electric field dependence coefficient decreases,and the dielectric constant and dielectric loss factor increase with the increase of aging time.