Performance Evolution and Aging Mechanism of XLPE Insulation for HVdc Cables After Different Accelerated Aging

In this article, the ±200-kV crosslinked polyethylene (XLPE) cable used in Zhoushan flexible dc transmission project is targeted. Three accelerated aging schemes of continuous electrical (CE) aging, intermittent electrical (IE) aging, and electrothermal (TE) combined aging are designed, and the simulation test platform is built accordingly. The lamellar samples, cut from the XLPE insulation of the spare cable, are aged for predetermined durations under different design stresses. The samples are tested for oxidation induction time (OIT), Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), thermal stimulation current (TSC), space charge, dc conductivity, and dc dielectric strength, and the variation of various performance parameters are summarized. By analyzing the correspondence between the variation trend of each parameter and the aging process, the feature parameters that can effectively characterize dc XLPE insulation performance are determined, and the aging mechanism of dc insulation is explored. The results show that both electrical stress and thermal stress are important factors causing insulation aging, and their combined effect will significantly accelerate insulation deterioration. In addition, compared with the CE stress, the rise and fall of dc voltage will also aggravate the aging to a certain extent. Therefore, after the same time of continuous electrical stress, IE stress, and TE combined stress, the aging degree of XLPE samples increases in turn.