Structural Alteration and Electric Field Estimation Inside HVAC Cable due to Inhomogeneous Aging

Under diverse loading conditions, high-voltage alternating current (HV-AC) underground polymeric cables exhibit a radial temperature gradient and experience differential thermal stress, resulting in inhomogeneous aging of the polymeric material. Consequently, a differential localized structural alterations occur at different radial positions within the insulation bulk of the cable. To investigate these effects, the authors have examined the cross-linked polyethylene (XLPE) insulation taken from HV-AC cables. Using a lathe machine, samples were extracted and subjected to various tests. The findings revealed significant variations in the morphology of the XLPE layers at different radial positions within the cable insulation bulk. These effects were further investigated by measuring the permittivity of samples extracted from different radial positions within the insulation bulk. The permittivity data is then fitted to field, temperature and radial position dependent equation, and the AC electric field distribution is estimated. The findings are also corroborated by AC breakdown tests.