Change of dielectric property with water-treed region

By dividing a water-treed XLPE sheet sample into a non-degraded layer and a water-treed one, relative permittivity ε_r2\´ and dielectric loss factor ε_r2^" of the water-treed layer have been estimated using an equivalent circuit. The way of changes in ε_r2\´ and ε_r2^" with the water tree length r estimated by the pulsed electroacoustic method has been discussed based on a Maxwell-Wagner-Sillars (MWS) model. It has been concluded that the MWS model gives a reasonable fit to the experimental data providing that the water conductivity in voids lies between 1×10^-3 S/m and 8×10^-3 S/m, and the minor and major axis ratio of the ellipsoids, to which water-filled voids are compared, lies in the range of 1:20 to 1:50