Time domain analysis of partial discharges at DC voltage in air and insulation oil

An important tool for the estimation of the insulation's condition in electrical devices is the partial discharge (PD) measurement. Under AC stress, the PD phase distribution can be used to classify the type and location of different defects. At DC voltage this approach is inapplicable. Therefore, other parameters for the classification of different PD-sources have to be identified. Here the pulse shape can provide information about the source of a measured PD. To prevent distortions of the PD-pulses by the measuring circuit a high frequency (HF) optimized setup is used to record the pulse shape. The pulse shape of corona in air and corona in mineral insulation oil is measured, analyzed and discussed.