Effect of Inhomogeneous Ageing of Insulation on Electric Field Distribution of a 220kV HVAC in-Service Cable

This paper primarily discusses about the phenomenon of inhomogeneous ageing observed in a 220 kV in-service 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 is expressed mathematically to vary along the radial position and is fitted with the experimental data. The fitted equations is 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 radial position, a significant enhancement in electric field in the middle part of cable insulation is observed. The Field Enhancement is visualized with different accelerated ageing permittivity data from the literature.