Small partial discharges and their role in insulation deterioration

It is a well known fact that PD (partial discharge) affects the lifetime and the deterioration rate of an insulation. Research work has shown that a mixture of magnitudes and frequencies of PD may appear, depending on the type of the applied voltage, its frequency, the electrode arrangement, the type of the insulation under test, and a number of other parameters, such as temperature, humidity and pressure. Various types of discharges also have been recorded, such as streamer like discharges, Townsend discharges, glow and pseudoglow discharges. A type of discharges not yet well understood is the so called SPMD (swarming partial microdischarges), which seem to appear just before breakdown. In this paper, only aspects of the latter type of PD are investigated. Some suggestions for further research regarding the SPMD are made