Development of Functional Dielectrics for Future All-Solid Substations

随着未来全固态变电站的发展，功能介电材料已成为研究和开发的目标。聚合物纳米复合材料被选为此类功能介质。这些材料在热性能、机械性能和电学性能方面比未填充的聚合物以及传统的微填充聚合物具有更大的优势。所研究的材料包括聚酰胺/层状硅酸盐纳米复合材料、环氧树脂/层状硅酸盐纳米复合材料、环氧树脂/二氧化钛纳米复合材料和环氧树脂/氧化铝纳米复合材料。利用扫描电子显微镜、原子力显微镜、X射线衍射仪、表面粗糙度计、能谱分析等手段对材料在局部放电和高局部电场作用下的降解过程进行了表征。主要研究结果如下：1.纳米膜与周围聚合物的界面是决定纳米复合材料性能的关键。在介观尺度上形成了一个相互作用区。2.从理论上考虑，提出了一个多核模型作为相互作用区的精细结构。它通常由三层组成，即第一层、第二层和第三层，从接触点到母体。3.首次发现聚酰胺/层状硅酸盐纳米复合材料比未填充的聚酰胺和填充微填料的聚酰胺具有更强的抗局部放电能力。这是首次在世界范围内发现纳米复合材料的优势。4.开发了一种独特的制备方法来制备实验室规模的纳米复合材料，特别是环氧纳米复合材料。5.环氧纳米复合材料不仅具有优异的局部放电性能，而且还具有良好的抗树枝效应。这些发现可以用所提出的多核模型来解释。6.我们惊讶地发现，纳米结构导致介电常数降低，而微填充聚合物的介电常数增加。它清楚地表明，界面是决定宏观参数的深层次因素。

With future all-solid substations, functional dielectrics have been targeted as R & D. Polymer nanocomposites were chosen as such functional dielectrics. These materials were found to be much advantageous over unfilled polymers as well as conventional micro-filler filled polymers in thermal, mechanical and electrical properties. Materials investigated include polyamide/layered silicate nanocomposites, epoxy/layered silicate nanocomposites, epoxy/titania nanocomposites, and epoxy/alumina nanocomposites. Materials are characterized by SEM, AFM, XRD, Surface Roughness Meter, EDX and the like, while they are subjected to partial discharge and high local electric field to degrade.Some of the outstanding results are summarized as follows :1.Interfaces between nanofillers and surrounding polymer matrices are crucial to determine the properties of nanocomposites. Those form an interaction zone in mesoscopic scale.2.A multi-core model is proposed as fine structures of the interaction zone from theoretical consideration. Typically it consists of three layers, i.e. the first kyer, the second layer and the third layer from the contact point toward the matrices.3.It was found firstly that polyamide/layered silicate nanocomposites are far more resistant to partial discharges than unfilled polyamide and micro-filler filled polyamide. This is the first discovery of nanocomposite advantage to have initiated such studies worldwide.4.A unique manufacturing method has been developed to prepare nanocomposites in laboratory scale, especially epoxy nanocomposites.5.Epoxy nanocomposites exhibit not only excellent partial discharge resistance but also treeing resistance. These findings can be explained in term of the proposed multi-core model.6.Permittivity decreases due to nanostrucuration as our surprise, while it increase for micro-filler filled polymers. It clearly shows that interfaces are deeply involved to determine macroscopic parameters.