This paper analyzes the microstructure and electrical insulation characteristics at the interface of 500 kV cross-linked polyethylene (XLPE) cable factory joints for extra high voltage direct current (EHVDC) application. The interface between two layers was polished by different grit sandpapers (80, 400, 1000, 2000, and 0000 (unpolished)). The samples (#1000) polished by 1000 grit mesh at the interface were degassed at 70°C for 0, 12, 36, 90, and 200 h, respectively. Physico-chemical and electrical experiments were performed on the prepared test samples. It is found that increasing the number of sandpaper grit meshes reduces the average lamellae thickness at the interface and increases the crystallinity. Moreover, microporous defects are observed at the interface. The parameters viz elongation at break, current density, and the number of microporous defects increase initially and then decrease. However, the space charge accumulation, threshold electric field strength, and DC breakdown decrease initially and then increase. Notably, the #1000 roughness is a turning point. On the other side, degassing treatment promotes the orderly folding and recrystallization of the molecular chains arranged the amorphous region and significantly reduces the microporous defects at the interface. The mechanical properties are affected to a certain extent. The improved microstructure reduces the space charge accumulation and the current density of the sample, and increases the DC breakdown strength. An interfacial microscopic model and a charge transport model are proposed to analyze the mechanism of material properties under different roughnesses and electric fields. The results indicate that the ultra-smooth interface and degassing treatment strengthen the molecular chain linking at the interface. Moreover, they significantly reduce the microporous defects at the interface and improve the insulation properties of the factory joint.

本文分析了用于超高压直流 (EHVDC) 应用的 500 kV 交联聚乙烯 (XLPE) 电缆工厂接头接口处的​​微观结构和电绝缘特性。两层之间的界面用不同粒度的砂纸（80、400、1000、2000 和 0000（未抛光））抛光。在界面处通过 1000 目抛光的样品 (#1000) 在 70°C 下分别脱气 0、12、36、90 和 200 小时。对制备的测试样品进行物理化学和电学实验。发现增加砂纸粗粒网格的数量会降低界面处的平均薄片厚度并增加结晶度。此外，在界面处观察到微孔缺陷。参数即断裂伸长率、电流密度、微孔缺陷的数量先增加后减少。然而，空间电荷积累、阈值电场强度和直流击穿先减小后增大。值得注意的是，#1000 粗糙度是一个转折点。另一方面，脱气处理促进了排列在非晶区的分子链的有序折叠和重结晶，显着减少了界面处的微孔缺陷。机械性能受到一定程度的影响。改进的微观结构减少了样品的空间电荷积累和电流密度，并增加了直流击穿强度。提出了界面微观模型和电荷传输模型来分析不同粗糙度和电场下材料性能的机制。结果表明，超光滑界面和脱气处理加强了界面处的分子链连接。此外，它们显着减少了界面处的微孔缺陷，提高了工厂接头的绝缘性能。