Effect of magnitude of space charges on the electric field distribution in XLPE insulation in presence of water trees

In this paper, we present a numerical simulation of the influence of water trees growing from semiconducting layers (in the interior and the exterior) in presence or not of space charges on the behavior of the cross-linked polyethylene (XLPE) insulation used in the medium voltage cables. Individual vented tree configurations are modeled under Comsol Multiphysics environment. To understand the mechanism of involved phenomena, an evaluation of the electric field distribution is carried out. The influence parameters adopted in this investigation are: the permittivity, the length of the water trees and the magnitude of the space charges. The results of investigation showed that, in the absence of space charges, water trees lead to a local increase (respectively decrease) of the electric field in the outside (respectively inside) areas of these trees. However, the accumulation of space charges induces a significant variation of electric field inside and outside the trees and in the volume of insulation. In fact, the electric field repartition depends on the magnitude of space charge density and space charge layer dimension. According to this repartition, the dynamic movement of the space charges is evoked.