Evaluation of surface- and corona discharges at DC voltage

Due to the rising number of DC transmission systems there is an increasing interest in partial discharge (PD) diagnostics at DC voltage. Under AC stress there are several established instruments to get evidence of the type and the location of the defect, most important the phase angle histogram. Under DC stress there are no such methods available up to now and therefore new interpretation techniques have to be developed. In this paper two typical types of PD are generated and analyzed on the basis of various parameters to identify characteristics which allow a founded differentiation of these two types of defect. The results are discussed on the basis of the physical processes which are involved in the discharge process.