Insight into Water Tree Characteristics of Radiation Aging XLPE Based on Repeated PDC Method

This paper investigates the water tree degradation process of nuclear power plant cables after irradiation by analyzing the water tree propagation characteristics and dielectric response changes during repeated polarization and depolarization. Firstly, cable samples with varying irradiation doses are obtained and subjected to water tree aging for 60 days. Then, the repeated polarization and depolarization current tests are carried out on these samples, and the standard deviation of DC conductivity as well as the difference for each time PDC test are calculated. Finally, the mechanical properties and aggregate structure of irradiated samples are obtained to analyze the characteristics of the water tree after irradiation. The results conclude that irradiation resulted in more pronounced water tree propagation in cables, with water tree lengths exceeding 500 μm after 1080 kGy radiation aging. The DC conductivity of water tree aging samples increases with the number of polarization and depolarization, and a positive correlation is observed between the standard deviation of DC conductivity and the average length of water tree branches. This phenomenon arises from the impact of irradiation on the crystal structure, leading to a relaxation of the crystal lattice, a reduction in intermolecular forces, and evident deformation within the water tree region under the influence of Maxwell stress. Radiation can also destroy the amorphous region, making it easier for deformation to accumulate and further increase the deformation of water tree region.