The behaviour of water in XLPE and EPR cables and its influence on the electric characteristics of insulation

This Gaper presents the latest results of continuous investigations of cable insulations degradation of crosslinked polyethylene (XLPE) and ethylene-propylene with rubber based formulation (EPR) what subjected to electric stress and heating in the presence of water or water vapour (this work is part 2, part I is (1)). The paper deals with water absorption and diffusion in two kinds of crosslinked polyethylene insulations - dry-cured and steam-cured, and steam-cured EPR insulation. The aim of this investigation is to present the results of the influence of changing of water or water vapour pressure in the conductors of XLPE and EPR cables in different service conditions on the electric characteristics of XLPE and EPR insulations - breakdown voltage (AC BDV), dissipation factor (tng delta) and rata of partial discharge (RPD). In this paper, RPD is defined as, the mnu. electrical field when the beginning partial discharge in the cable insulation and partial discharge were measured in acc, tc,IEC, standard. This paper also shows the relation between AC BDV and water content. and AC BDV and tng delta in XLPE and EPR insulations, In this testing, the tap water was put in the cable conductors and the ends were properly closed by terminal boxes (1). The results indicate that the combined effects of water or water vapour, pressure, moisture, electric field and temperature will greatly accelerate deterioration of XLPE and EPR insulations.