Effect of Aggregation Structure on DC Electrical Performance of Thermo‐Oxidatively Aged Crosslinked Polyethylene Insulation

ABSTRACT Thermal ageing is an important factor leading to the deterioration of crosslinked polyethylene (XLPE) cable insulation. In this paper, XLPE insulating material was prepared in the laboratory and treated by thermal ageing at 130°C for durations of up to 40 days. Space charge and DC electrical breakdown characteristics were investigated to evaluate the DC electrical performance of differently aged XLPE. Furthermore, to gain deeper insight into the underlying mechanisms, the charge trap characteristics along with the chemical and crystalline structures were examined. The results show that, during the effective protection period of the antioxidant, the XLPE samples exhibit enhanced DC electrical performance, specifically higher DC breakdown strength and reduced space charge accumulation. This improvement is attributed to the evolution of the microstructure. In the initial ageing stage, the degree of crystallisation increases, whereas physicochemical defects are reduced, accompanied by a more concentrated trap energy distribution. As a result, charge injection and migration are effectively inhibited. In the later stage of ageing, the antioxidant efficacy weakens and molecular chain scission occurs, resulting in the disappearance of spherulitic structure and deterioration of electrical properties. These findings are essential for the understanding of the XLPE cable service performance and the enhancement of the XLPE DC electrical performance.