Aging-Induced Trap Evolution and Breakdown Strength in LDPE: Numerical Modelling Approach

High-voltage polymeric insulators are critical components in power systems, but they inevitably degrade due to aging under strong electric fields and thermal stress. In this study, we investigate the relationship between changes on a molecular level and the macroscopic reduction in the breakdown strength of low-density polyethylene (LDPE). During thermo-oxidative degradation, impurity functional groups and concentrated electric fields induce changes in the electronic structure of the polymer by creating deep traps that elevate the risk of electrical failure. These insights were integrated into a bipolar charge transport (BCT) model and a molecular chain displacement (MCD) model, which enables a comprehensive numerical analysis of space charge accumulation and breakdown mechanisms. Numerical analysis shows that an increase in deep trap energy (by 1.15 times) and trap density (by 2 times) significantly influences space charge behavior. Moreover, slight variations in shallow traps moderately affect conduction but do not dominate changes in breakdown strength. Our results demonstrate that local chain rearrangements and polymer relaxation times critically determine whether higher deep trap energies lead to increased or decreased breakdown strength at the aging stage. These findings provide quantitative insights for predicting breakdown strength under evolving aging conditions.