Behavior of voltage-current characteristics and threshold indications for XLPE-based materials

Additives have been introduced in the conventional high-voltage grade XLPE, with the purpose to modify the electrical threshold level. The electrical threshold is estimated through the steady-state current-voltage characteristic obtained from dc charging current measurements performed at different voltage levels. Space-charge distribution observations are carried out, by PEA, in order to confirm the threshold values detected by charging-current measurements, having associated the threshold to the limit value above which space charges are steadily trapped in insulation. Significant variations of the electrical threshold levels is actually observed in the two tested additivated compounds, with respect to the reference XLPE. The conduction mechanism, phenomenologically attributed to space-charge limited current (SCLC), is rediscussed on the basis of space-charge distribution observations which show deviations from the SCLC theory