The Effects and Mechanisms of Thermal Oxygen Aging on Trap Characteristics and Electrical Performance of Functional Group‐Grafted Materials for HVDC Cable Insulation

Abstract

ABSTRACT In this study, N‐allylaniline (NA), a functional monomer possessing both deep trap‐inducing and antioxidant capabilities, was grafted onto cross‐linked polyethylene (XLPE) to prepare XLPE‐g‐NA. Both XLPE and XLPE‐g‐NA were subjected to thermo‐oxidative aging, and their physicochemical and electrical properties before and after aging were systemically investigated. For pure XLPE, carbonyl groups introduced during thermo‐oxidative aging formed electron traps, which reduced the conductance current at low temperature and suppressed space charge accumulation. However, these traps were insufficiently deep to capture carriers under high‐temperature and high‐electric‐field conditions, resulting in increased conductivity due to the accumulation of aging impurities. For XLPE‐g‐NA, amino groups were oxidized into hydroxylamines upon aging, which decreased the hole trap depth and shifted the primary deep trapping mechanism from hole‐dominated to electron‐dominated. Consequently, the polarity of accumulated space charge inverted from positive to negative, and the suppression of carrier transport was weakened at elevated temperatures. Nevertheless, aged XLPE‐g‐NA maintained superior and more reliable electrical performance compared to pure XLPE. This work demonstrates that evaluating the impact of thermo‐oxidative aging on the electrical performance of polymeric insulation requires considering molecular structural changes that govern trap distribution characteristics.