Relative Permittivity and Conductivity of Water-treed Region in XLPE Estimated by an Equivalent Circuit

By dividing a water-treed XLPE sheet sample of 1 mm thickness into a non-degraded region and a water-treed one, relative permittivity εr2' and ac conductivity σAC2 of the water-treed region have been estimated using an equivalent circuit. The way of changes of εr2' and σAC2 with the length r of the water-treed region has been discussed based on the Sillars model. It has been concluded that the volume fraction of water in the water-treed layer is in the range of 0.5 % to 1.5 % for the most-degraded XLPE sheet, which depends on the ratio of axes of spheroids to which water-filled voids and channels are compared. It is also concluded that ac conductivity of water in the water-treed region is in the range of 3×10-3 S/m to 2×10-2 S/m.