Partial discharges in flat, dielectric/metallic bounded cavities

Investigations were made on the character of partial discharges (PD) in samples with a flat, air-filled, cylindrical cavity (height 0.1 mm) with one dielectric and one metallic wall. Images of discharge sequences in the cavity were recorded with a streak camera to determine the temporal and spatial development of the discharges. Simultaneously, the electrical signal as detected on the measuring electrode is displayed on a 1 GHz real time oscilloscope. Some characteristic pulse shapes are observed, which could be related partly to the discharge image. PD analyses (phase/height) are performed using an ultrawideband measurement system. The resulting pulse shapes and PD patterns are compared to those recorded from PD studies with spherical voids. Correlations between PD characteristics and types of defects in electrical insulation are discussed.