Dielectric behavior and physico-chemical properties of 60 kV HV crosslinked polyethylene under long-term electrical aging

This study focuses on the study of long-term electrical aging effects on dielectric behavior of cross-linked polyethylene (XLPE) used as insulation in high voltage cables. For this reason, we have performed long-term electrical aging tests on full size of HV 36/60 kV XLPE cable samples at three voltage levels (U0 = 36 kV, 2U0 = 72 kV and 3U0 = 108 kV) during 680 hours. The studied properties are partial discharge threshold, dielectric loss factor, relative permittivity and transverse resistivity. Besides, physico-chemical changes were assessed using Fourier Transform Infrared Spectroscopy (FTIR) and X-ray diffraction (XRD). In the end of paper, the evolution of mechanical properties and hot set test with aging time and voltage levels have been presented and analyzed as additional diagnostic precursors. The obtained results illustrate that examined properties are widely affected by long-term electrical aging. The increase in partial discharges and dissipation factor depending to the voltage level and the aging time and the decrease in partial discharge threshold voltage and transverse resistivity are the mostly marked degradation precursors. These degradation precursors are supported by the increase of carbonyl groups and reduction in the crystallinity degree of the polymer under long-term electrical aging. These parameters are useful parameters for evaluating the quality of underground XLPE cable insulator.