High Repetition Rate Space Charge Measurement of Heat-treated Low-density Polyethylene at Prebreakdown

Prebreakdown is a transient process and the external electric field at prebreakdown is widely used to evaluate dielectric performance of polymeric materials without considering space charge effects. In this study, a 1-ms high repetition rate pulsed electro-acoustic (PEA) system was developed to observe space charge evolution in heat-treated low-density polyethylene (LDPE) films at prebreakdown under a linear ramping voltage of 1.5 kV/s at 70°C. The continuous recording time was 30 s. The results show that the maximum internal field, which was nonlinear with the linear ramping voltage, of heat-treated LDPE films at prebreakdown is similar. Before prebreakdown, ice-water cooling LDPE films appeared multiple positive space charge packets and alternately migrated towards the cathode, while air cooling and slow cooling LDPE films existed a large number of negative charge injection, migration, and accumulation. At prebreakdown, the maximum field distortion ratio of all heat-treated LDPE films exceeded 40% due to space charge accumulation, which could provide new ideas and data support for evaluating the breakdown characteristics of insulating materials considering space charge effects.