Mechanisms and performance effects of by-product transformation during degassing of XLPE cable insulation materials

The dynamic changes of by-products during degassing of ultra-high-voltage(UHV) cross-linked polyethylene (XLPE) cable insulating materials and the mechanism of their influence on the performance are still unclear, which restricts the development of domestically produced insulating materials and the optimization of the process. In this study, 220kV XLPE insulating material was used as the target material. By comparing the composition and property changes of by-products in cable segments (Cable) and molding specimens (Bulk-1 and Bulk-2) under different degassing times, and combining gas chromatography-mass spectrometry (GCMS), infrared spectroscopy (FTIR) and mechanical/electrical property tests, the multistage transformation laws of by-products and their effects on insulation properties were investigated. The results showed that the dicumyl peroxide (DCP) decomposition products (e.g. acetophenone, α-styrene) were gradually converted into small molecules such as propane and butene during degassing at 70°C, and the degree of conversion was positively correlated with the degassing time. The Cable has more complex by-products due to impurities in the shielding layer, while the molding specimen (Bulk-2) has the lowest acetophenone content and the best electrical properties (significant increase in breakdown strength) after 20 days of degassing, and the mechanical and electrical properties of the outer samples are better than those of the inner samples. The study confirms that the reduction of macromolecular by-products such as acetophenone can significantly improve the insulation performance, which provides a key experimental basis for optimizing the degassing process and formulation design.