Effect of Inhomogeneous Aging of Insulation on Electric Field Distribution of a 220 kV HVAC In-Service Cable

This article primarily discusses the phenomenon of inhomogeneous aging observed in a 220 kV in-service high voltage alternating current (HVAC) cable. The XLPE layer is peeled out circumferentially using a special lathe. The samples are subjected to various material characterization tests including Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), differential scanning calorimetry (DSC), and dielectric spectroscopy. The results show significant differences in morphology among XLPE layers, which is in turn reflected in permittivity measurements. The local changes in permittivity are expressed mathematically to vary along the radial position and fit with the experimental data. The fit equations are used to estimate the electric field distribution inside the insulation bulk using a finite element method (FEM) software. The simulation results are also verified analytically. When compared to conventional field distribution with bulk consideration of permittivity and permittivity at the radial position, a significant enhancement in the electric field in the middle part of cable insulation is observed. The field enhancement is visualized with different accelerated aging permittivity data from the literature.