Charge transport mechanism of cross‐linked polyethylene/silicone rubber composite insulation by energy band theory

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.