Study of ultra-fast space charge in thin dielectric films

A novel method, based on the short circuit current measurement, is proposed to detect ultra-fast detrapping space charge. A Rogowski coils based pulse current probe was used to measure the discharge current spectrum of polypropylene film previously subjected to DC high field. The typical results show that the characteristics of damped oscillation with the quasi period several tens nano-seconds. The quasi periods of the damped oscillation decrease within the duration of space charge discharge. The features of the changing quasi periods are applied field intensity dependent. The period hardly changes for low applied field intensity, while the periods were found to change by about forty percent for high applied field intensity. The phenomenon was thought to be related to space charge behavior, which may influence on the equivalent capacitance of the film samples. Based on the analysis of the damped oscillating discharge current spectrum, the model of space charge transport mechanism for the ultra-fast discharge procedure of the charged sample was proposed.