Effect of semiconducting screen on the space charge dynamic in XLPE and polyolefin insulation under dc and 50 Hz ac electric stresses conditions

In the past two decades, significant advances in space charge measurements in polymers have resulted in a better understanding of charge dynamics and their effect on material selection and processing. However, little attention has been given to the effect of semiconducting screens on space charge formation in the bulk insulation. This paper reports on space charge measurements on similar to 1.5 mm thick XLPE and polyolefinic plaques with different treatments and semicon electrodes, using the modified laser induced pressure propagation (LIPP) system. Samples were subjected to do or 50 Hz ac electric stresses in the region of 25 kV/mm at ambient temperature. Emphasis has been placed on comparing the space charge characteristics of the two insulation systems with different semicon electrodes using an established method termed "X-plots" for analyzing data. The effects of sample treatment (i.e. degassing) on the space charge dynamics are also presented.