The Analysis of PD-Sequences from Different Defects

At the first glance partial discharge processes seem to occur to a large extent at random. But this appearance is often due to the fact, that in many cases partial discharge processes are influenced by local charge accumulations in the region of the defect that are generated by the discharges themselves. Especially in solids these charges prevent the ignition of the next consecutive discharge until the field reset generated by the preceding discharge is overcome, either by a change of the external voltage or by a decrease of the local accumulation of charges. The analysis of pd sequences and not solely data sets accumulated on the basis of the phase angles of occurrence only - revealed the influence of surface and space charges generated by the individual partial discharges. To examine these phenomena in more detail, the pd activity of different types of electric equipment was measured with constant and ramped voltage load. The results revealed that different defects behave differently. The underlying physical phenomena - and especially the influence of the surface conductivity of inner or outer surfaces - will be discussed. In many cases, especially with large scale test objects more than one pd source may be active. The pd signals from different spots may be separated by means of the Pulse Shape Analysis, that uses the distortion of the original signals on the way to the coupling device