Mathematical Modeling of Electric Current Distribution in Water Trees Branches in XLPE Power Cables Insulation

Abstract

During the long-term operation of power cables with cross-linked polyethylene (XLPE) insulation, moisture inevitably accumulates in them, forming thin branched structures filled with water - water trees. They are considered to be the main cause of insulation degradation. The features of electric current distribution in the branches of water trees in XLPE insulation of power cables were studied. Mathematical modeling of the current density arising in the trees under the influence of an external electric field was carried out for their most characteristic configurations, according to experimental data. The dependences of the maximum values of the current density are established depending on the dimensional parameters of the trees branches (length, geometric shape, angle of inclination and walls curvature for narrowing). The simulation was carried out by the finite element method in the Comsol software environment. Nonlinear properties of insulation in strong electric fields (which appears in ultra-high voltage cables above 110 kV) was taken into account. The obtained information improves the understanding of the degradation mechanisms in XLPE insulation regarding the occurrence of electrothermal processes.