Fundamental studies of the influence of the morphology of cross-linked polyethylenes on the accumulation and mobility of space charges

交联低密度聚乙烯（xLDPE）由于其非极性特性、高体积电阻和低损耗因数，已成为高压技术领域交流元件绝缘的有机绝缘材料。由于能源转换引起的潮流变化，德国电网发展规划将高压直流输电作为远距离输电的解决方案。这改变了使用过的电介质中的电场应力。高分子绝缘材料在高直流场应力下容易产生空间电荷积累。从组件设计的角度来看，必须避免这种情况，因为电介质受到额外的场载荷，这反过来会导致聚合物的老化增加，从而减少组件的使用寿命。初步研究表明，xLDPE中空间电荷的积累受其结构和形貌的影响。本项目的目标是从根本上研究高直流应力下xLDPE的结构和形态与空间电荷的形成、积累和迁移之间的相互作用。由于，特别是在交联聚乙烯的情况下，不仅结构（分支度，交联度），而且它们的形态（晶体的类型，排列和取向，结晶度，取向等），因此，它们的热性能（松弛温度，熔化温度）可以在很大范围内受到影响，因此将产生具有确定结构和形态的xLDPE试样。利用脉冲电声方法（PEA）对空间电荷积累进行分析，并推导出结构-性能关系。该项目的实现需要高分子科学与高压工程的协同合作。

Cross-linked low-density polyethylene (xLDPE) has established itself as an organic insulating material for the insulation of AC components in the field of high-voltage technology due to its largely non-polar character, high volume resistance and low loss factor. Due to the change of power flow caused by the energy transition, high-voltage direct current transmission is used as a solution for long distance power transmission in German grid development planning. This changes the electric field stress in used dielectrics. It is known that polymer insulating materials tend to accumulate space charges under high DC field stress. From the point of view of component design, this must be avoided, since the dielectric is subjected to additional field loading, which in turn leads to increased aging of the polymer and thus to a reduction in the lifetime of the component. Preliminary work shows, that the accumulation of space charges in xLDPE can be influenced by its structure and morphology. The goal of this project is to fundamentally investigate the interactions between the structure and morphology of xLDPE and the formation, accumulation and mobility of space charges under high DC stress. Since, especially in the case of cross-linked polyethylenes, not only the structure (degree of branching, degree of cross-linking) but also their morphology (type, arrangement and orientation of crystals, crystallinity, orientation, etc.) and, consequently, their thermal properties (relaxation temperatures, melting temperature) can be influenced within wide limits, xLDPE test specimens with a defined structure and morphology will be produced, analyzed with the pulsed electro-acoustic method (PEA) regarding the space charge accumulation, and structure-property relationships will be derived. Cooperative collaboration of polymer science and high voltage engineering is required for realizing this project.