Comparative investigation on pulse shape parameters of partial discharges in air under AC and DC voltage stress

In order to identify the type and the location of fault, partial discharge diagnosis is a valuable method. Until now, a majority of the evaluation criteria used for partial discharge diagnosis is based on investigations performed at AC voltage. The increasing importance of DC transmission systems requires additional research concerning the behaviour of partial discharges at DC voltage. Especially with regard to the different dominating physical processes and the associated influence on the appearance of partial discharges, a comparison of the behaviour under AC and DC voltage stress is necessary. By focussing on the pulse shape, two typical types of fault in air are emulated and stressed at AC and DC voltage under comparable test conditions. The pulse shapes occurring under negative and positive voltage stress are captured with a broadband measuring circuit. Characterizing parameters such as the rise time, the pulse width and the fall time are analysed, compared to each other and discussed.