Influence of DC and impulse voltage prestressing on the AC breakdown strength of aged (XL)PE-20 kV cables

The main reason for the deterioration of the electric strength of directly buried MV cables with extruded insulation is water treeing (WT). In networks, WT develops in a slow process over the years. It is assumed that this process can be simulated under accelerating conditions in laboratories. The authors describe tests which show that the chosen prestressings (DC, DC with flashovers, impulse voltage, AC 0.1 Hz) do not influence the electric strength measured by an AC step rise test neither from laboratory aged 20 kV XLPE nor from 17 year old field aged 20 kV PE cables