In stress space charge probing during ageing of polymeric samples

Charge injection is known to occur in the prebreakdown stage in polymeric materials. It has recently been demonstrated that a time-resolved measurement of this charge is possible in a double-needle electrode configuration and under AC voltage using an analog experimental setup with a sensitivity of approximately=10/sup -14/ C. A critical field for charge injection has been defined in two polymeric materials (polyethylene and epoxy resin). The authors report data on the temporal evolution of the charge during AC polarization. Results show that continuous space charge injection occurs during ageing of the polymeric samples. Some of the injected carriers are permanently trapped in the dielectric.<>