界面效应对纳米复合交联聚乙烯空间电荷特性的影响研究

Recently, the influences of nano-composites on space charge transport process in solid dielectrics is becoming hot topic in research area. Due to lacking of literature on the interface effect of nanodielectrics and the effective microscopic theory model, further experiments and theories are urgently required in the engineering application field of cross-linked polyethylene (XLPE) nanocomposites. This project intends to use melt blending extrusion method to study the preparation technology of XLPE nanocomposites, especially solving the dispersion problem of nanofillers. Moreover, this project utilizes microscopic observation, material analysis, and high voltage testing technology, and systematically carries out experimental study which focuses on the influence of interface effect on the production and distribution of space charge in the XLPE nanocomposites under different conditions. Based on physical and chemical performance experiments, the molecular chain structure and defect characteristics of the interface of nanofillers can be derived. Then the local potential field, polarization strength, and energy state distribution of electron traps around the interface can be computed, which could contribute to the establishment of the double layer polarization model that illustrates the physical and chemical characteristics of interface quantitatively. From the study above, this project will solve the nanofiller dispersion problem during the preparation of XLPE nanocomposites, illustrate the influence of interface effect of nanofillers on the space charge characteristics, reveal the internal mechanism of interface effect on the microscopic material parameters and macroscopic electrical performance of XLPE nanocomposites, and provide experimental and theoretical support for the high voltage DC cable technology.

纳米复合对电介质内部空间电荷输运过程的影响是当前研究热点，但由于缺乏对纳米复合电介质界面效应深入的认识、有效的微观模型和理论，纳米复合交联聚乙烯的工程应用急需充分的试验和理论依据。本项目拟采用熔融共混挤出法，研究纳米复合交联聚乙烯的制备工艺,着重解决纳米粒子分散性问题。综合微观观测、材料分析和高电压测试技术，系统开展不同的工况下界面效应对纳米复合交联聚乙烯空间电荷产生机理和分布规律影响的试验研究。通过基础理化性能测试获得纳米粒子界面分子链构形和缺陷特性，计算界面局部势场、极化强度和陷阱能态分布，建立定量描述界面物理和化学性质的双电层介质球极化模型。通过上述研究，解决纳米复合电介质制备过程中纳米粒子分散性问题，阐明纳米粒子形成的界面效应对空间电荷特性的影响机理，揭示界面效应对纳米复合交联聚乙烯微观材料参数和宏观电气性能的内在作用机制，为高压直流电缆技术提供试验和理论支持。

作为高压直流输电技术的重要组成部分，直流电缆技术的发展受到空间电荷问题的极大制约。本项目综合有机合成、纳米技术、高电压测试、数值仿真等交叉学科技术，紧紧围绕纳米颗粒表面接枝对交联聚乙烯（Cross-linked polyethylene, XLPE）空间电荷特性的影响展开研究，并对优选参数组别进行陷阱特性和电学性能测试，以期为高压直流电缆用绝缘材料的研发提供材料、工艺、试验和理论的支持。. 纳米SiO2表面接枝及其表征：1）制备了不同纳米形貌和不同小分子接枝密度、基团极性类型的纳米SiO2；2）RAFT法制备了适用于聚乙烯体系的聚甲基丙烯酸十八烷基脂（Poly(stearyl methacrylate), PSMA）表面接枝纳米SiO2；3）获得了定量调控PSMA接枝密度和分子量的关键工艺参数，及功能基团表面接枝工艺。. 对空间电荷测量系统进行改进，提高了耐高温（90℃）能力，实现了压力的定量调控和高速动态测量能力（0.1 ms）。. 通过小分子接枝纳米SiO2/XLPE的空间电荷特性测试，发现：1）随接枝密度增加，空间电荷注入深度和注入量均先减小后增大；2）非极性小分子接枝有利于纳米SiO2与聚合物相容，改善高场空间电荷分布。. 通过聚合物刷PSMA接枝纳米SiO2/XLPE空间电荷特性的测试，发现：1）0.04 – 0.15ch/nm2范围内，接枝密度越小，空间电荷抑制效果越好；2）10 – 90kg/mol范围内，分子量在45kg/mol时空间电荷抑制效果比较理想；3）透射电镜图像定量统计表明空间电荷抑制效果较好的组别纳米颗粒分散效果也较好。. 优选参数PSMA_SiO2/XLPE组别电导电流幅值最小，Weibull分布63.2%概率直流电气强度较纯XLPE提高35.4%，达413kV/mm。给出一种电极/电介质界面深陷阱效应的空间电荷抑制模型和机理解释。. 本项目的研究紧紧着眼于高压直流电缆绝缘遇到的空间电荷问题，获得了大量试验结果，可为直流电压下空间电荷有效抑制技术提供重要支持。