Space charge measurements in XLPE insulation under 50 Hz ac electric stress

Space charge is believed to play an important role in electrical ageing of polymeric insulation, particularly where electric tree initiation is the dominant cause of premature failure of the material. However, space charge trapping and dynamics under ac operating conditions are not fully understood. This paper reports on an on-going investigation into the measurement of space charge in cross-linked polyethylene (XLPE) insulation subjected to 50 Hz ac electric stress. This paper describes the main features of the laser induced pressure pulse (LIPP) method used for the ac space charge measurements. Preliminary results of the charge and electric stress distributions in as received and degassed XLPE plaque samples stressed at ac stress of up to 30 kV/mm_peak are also presented