Effect of Tensile Stress on Insulation Properties of 500 kV EHVAC XLPE Cable Under Multi-Field Ageing

Using submarine cables to connect offshore wind farms and oil drilling platforms for power transmission and distribution has become the optimal choice for offshore energy projects. Studying the impact of complex laying environments during the actual operation of extra-high voltage AC (EHVAC) cross-linked polyethylene (XLPE) submarine cables has become imminent. This study investigates the impact of multi-field ageing on the insulation properties of 500 kV EHVAC submarine cables. The ring-cut samples with a thickness of 0.15 mm are aged at a fixed temperature of 110°C and electric field of 20 kV/mm, while being subjected to varying tensile stresses from 30 N up to 80 N. The aged XLPE samples are analyzed through crystalline analysis, dielectric properties and AC breakdown measurements at 30°C and 70 °C. The results suggest that as tensile stress increases, aged samples exhibit a notable reduction in crystallinity and AC breakdown strength, alongside an improvement in the dielectric constant. It concludes that stretching the XLPE samples leads to molecular chain breakage, resulting in an increase in defects between lattices and amorphous regions, consequently making the polarization easier to establish. Also, the increase of the tensile stress will accelerate the degradation of the insulation layer of the 500 kV EHVAC submarine cables.