In this paper, the residual electric field computation in a cable insulation in the presence of water trees and space charge is presented. Considering that, in treed areas, the variations of the permittivity and the space charge density are known, the thermal step current Ic(t) is computed and the curves Im (t) and Ic(t) are compared. The results show an important increase of residual electric field for some dimensions and concentrations of the water trees (up to 10 MV/m). Finally, the influence of the residual electric field on electrically aged cable insulations is analyzed.

Keywords: Cable insulation, Electric field, Space charge, Water treeing.