Space charge, local electric field and partial discharges

Pulse sequence analysis has shown, that space charges generated by previous partial discharges determine the further sequence of discharges. The method has proven to be very efficient in characterizing the defect type and-under certain conditions-even the location in an apparatus. Especially the voltage change /spl Delta/U between consecutive discharges has been shown to be a very meaningful parameter. In some cases tiny, non detectable currents may flow independent of a partial discharge event and generate additional space charges that influence the ignition of the consecutive discharge. The analysis of partial discharge sequences in commercial apparatus revealed that at different times different 'homogeneous' subsequences exist. They may be separated by discharge free time intervals and can be used to characterize different technological defects. Also in this context local space charges and their change with time play a dominant role.