Molecular displacement electrical breakdown model and its application to XLPE

Abstract Cable transmission is crucial for long-distance power transfer, connecting regional power grids, and integrating wind farms into the grid, serving as a key element of high-voltage direct current power systems. Nonetheless, during operation, the cross-linked polyethylene (XLPE) insulation layer in cables is frequently subjected to electro-thermal coupled stresses, which significantly impacts the cable’s safety and transmission efficiency. This study investigates systematically different types of XLPE samples in terms of their physicochemical and electrical properties. It is found that increasing sample thickness reduces breakdown performance significantly, with a maximum decrease of 64.94%. Increasing temperature also degrades breakdown strength, with a maximum reduction of 25.27%. However, there are certain discrepancies between the experimental data and the calculated results of classical breakdown models regarding the temperature and thickness dependence of breakdown strength. It also finds that XLPE’s crystallinity, gel content, and grain size are positively correlated with the breakdown strength. Thus, from the perspective of molecular chain motion, this study establishes a molecular displacement electrical breakdown model for XLPE under electro-thermal coupling fields based on potential barriers and molecular chain displacement mechanisms. Its calculations agree well with experimental data, with error less than 4.17%. Moreover, it can simultaneously simulate how breakdown strength varies with temperature and thickness, breaking the limitation of classical models that only simulate a single variable. It reveals the performance evolution and breakdown mechanism of insulating materials under multi-field coupling, providing the theoretical basis for high-voltage insulation materials design.