Properties estimation of inhomogeneous dispersive materials by electromagnetic modeling and dielectric spectroscopy

An electroquasistatic numerical model of polyethylene insulation affected by water trees is proposed in this study. The model includes dispersive materials (polyethylene and water trees) having the properties set after processing experimental results obtained by dielectric spectroscopy in the frequency range 10^-2-10⁶ Hz, combined with the usage of two semi-analytical models for effective permittivity of dielectric mixtures. The numerical model is implemented in the finite element method of the software package COMSOL Multiphysics. The solution of the proposed model was computed for all frequencies tested in dielectric spectroscopy measurements, and the effective permittivity (real part) and loss tangent as resulting from the numerical model were compared with the experimental ones. The modeling results are close to the experimental data, thus showing that the inverse problem approach proposed in this work leads to a good estimation of the frequency dependent behavior of dielectric inclusions, such as the water trees grown in polyethylene insulation.