Space charge development and breakdown in cross-linked polyethylene under DC fields

Space charge development in cross-linked polyethylene (XLPE) was investigated using the Thermal Step Method (TSM). The samples were subjected to DC fields of ~25, 50 and 70 kV/mm and, several times during aging, the TSM, which is a nondestructive technique, was used to measure insulation response current. The distribution of the corresponding space charge was computed using the newly developed inverse matrix technique. The insulation response current increased systematically with the time of voltage application. Under similar aging conditions some specimens were found to develop space charge faster than others. These specimens have consistently failed sooner than those with slower rate of space charge buildup. It is proposed that the initial rate of space charge development in polymeric insulation could provide an indication of its performance under DC field