Direct observation of time-dependent space charge profiles in XLPE cable under high electric fields

Space charge distribution was measured, applying an electric field of > 1 MV/cm to 3 mm thick XLPE cable insulation. Improving the conventional pulse electro-acoustic method, a new method was developed to measure space charge when applying HV to cables. Under high field, hetero charges were formed soon after voltage application, followed by an injection from the cathode. Then intermittent injections of charge packets from the anode took place. The space charge distribution kept changing without becoming stabilized. A simulation was done assuming hysteresis of the injection characteristics. The observed intermittent injection near the anode was qualitatively reproduced using computer simulation.