First electron availability and PD generation in insulation cavities

An investigation on the behavior of partial discharges occurring in insulation cavities as a function of environmental conditions is presented in this paper. In particular, focus is made on peculiar conditions where semi-transparent insulation is subjected to different visible light intensity, is irradiated by UV or is kept in the dark. Experiments are carried out on cells with an artificial defect, obtained producing a spherical void in epoxy resin. It is shown that not only PD inception voltage is sensitive to fight wavelength and intensity, but also PD average delay time changes considerably. It can be speculated that inception voltage can be related prevailingly to either background radiation or field-assisted electron detrapping from defect surfaces, depending on defect geometry and environmental conditions.