Study on aggregation structure and dielectric strength of XLPE cable insulation in accelerated thermal-oxidative aging

In order to study the influence of accelerated thermal-oxidative aging on aggregation structure and dielectric strength of XLPE insulation, The X ray diffraction (XRD), scanning electron microscope (SEM), differential scanning calorimetry (DSC) tests, ac breakdown experiments and oxidation induction time (OIT) experiments were done. Depending on the results that OIT decreases dramatically and then is close to 0, the aging process can be divided into two stages. In the recrystallized stage, the crystallinity, melting temperature and breakdown field strength increase slightly. Meanwhile, the OIT decreases significantly, which reflects the antioxidant is consuming. In the thermal-oxidative aging stage, however, the crystallinity, melting temperature and breakdown field strength decrease dramatically. The OIT is close to 0, indicating the antioxidant is exhausted. During this process, macromolecules break into small molecules, which create chain scissions and oxidation products. The thermal-oxidative aging model depending on thermal expansion and oxidation reaction is presented to explain degradation of aggregation structure and dielectric strength of XLPE insulation in accelerated thermal-oxidative aging.