The Role of Accumulated Charges in Partial Discharge Processes

A partial discharge in a solid dielectric or a commercial insulation consisting of different insulating materials often generates local charge accumulations that change the local electric field in the surrounding of the defect. Hence the conditions for the ignition of the following discharge are changed. Consequently in many cases a correlation between consecutive partial discharges exists that can be used for a better understanding of the local degradation processes. The Pulse Sequence Analysis has shown that space charges generated by previous partial discharges determine the further sequence of discharges and the method has proven to be very efficient in characterizing the defect type. Especially the time difference Δtn and the voltage change ΔUn between consecutive discharges have been shown to be very meaningful parameters. In the paper it will be shown from measurements on different electric apparatuses, in how far the partial discharge phenomena are influenced by charges accumulated as the consequence of prior discharges.