The composite insulation composed of cross-linked polyethylene (XLPE) and silicone rubber (SiR) is common in high voltage direct current cable accessory installation. However, the space charge accumulation, especially the interfacial charge accumulation of XLPE/SiR, poses a serious threat to the safe operation of cable accessories, and its charge transport mechanism is still unclear, especially at the micro-scale. In order to investigate the charge transport mechanism of XLPE/SiR, simultaneous measurement of space charge and relaxation current is performed on XLPE/SiR at various electric fields with different polarities, and the electronic energy levels of XLPE and SiR are determined by quantum chemical calculation (QCC). The results of QCC show that both the hole traps and the electron traps in XLPE are mainly shallow traps. As for SiR, the hole traps are shallow traps, while the electron traps are deep traps. The results of simultaneous measurement show that the interfacial charge accumulation and the composite conductivity of XLPE/SiR are significantly different under different polarities, that is, there is an obvious polarity effect. Based on the results of QCC, the electronic energy levels of XLPE/SiR system are constructed considering the interface between XLPE and SiR, as well as the interfaces between the materials and the electrodes. On this basis, the charge transport mechanism of XLPE/SiR is discussed in detail, and the polarity effect is well explained, which is believed to be related to the differences in the charge injection barrier and the interfacial barrier under different polarities, as well as the electron/hole traps in XLPE and SiR.

中文翻译：

---

能带理论研究交联聚乙烯/硅橡胶复合绝缘材料的电荷输运机理

由交联聚乙烯（XLPE）和硅橡胶（SiR）组成的复合绝缘在高压直流电缆附件安装中很常见。然而，空间电荷积累，特别是XLPE/SiR的界面电荷积累，对电缆附件的安全运行构成严重威胁，其电荷传输机制仍不清楚，特别是在微观尺度上。为了研究XLPE/SiR的电荷传输机制，对XLPE/SiR在不同极性的不同电场下进行空间电荷和弛豫电流的同步测量，并通过量子化学计算确定XLPE和SiR的电子能级（质量控制委员会）。QCC结果表明XLPE中的空穴陷阱和电子陷阱均以浅陷阱为主。对于SiR，空穴陷阱是浅陷阱，而电子陷阱是深陷阱。同时测量结果表明，不同极性下XLPE/SiR的界面电荷积累和复合电导率存在显着差异，即存在明显的极性效应。基于QCC的结果，考虑XLPE和SiR之间的界面以及材料和电极之间的界面，构建了XLPE/SiR系统的电子能级。在此基础上，详细讨论了XLPE/SiR的电荷传输机理，并很好地解释了极性效应，认为这与不同极性下电荷注入势垒和界面势垒的差异有关，以及XLPE 和 SiR 中的电子/空穴陷阱。