Surface discharge imaging in presence of deposited space charges in non-uniform DC electric field

An investigation is made of the influence of an accumulated charge sprinkled on the surface of an epoxy resin plate in corona mode on partial discharge inception and its forms as analyzed by optical imaging at DC voltage. The effects of the polarities of both the deposited hetero- and homocharges were investigated. The occurrence of first streamer discharges was detected electrically and observed by optical imaging. The various forms of streamers were acquired by optical imaging and associated with the polarity and intensity of the accumulated surface charges. Surface charge sprinkling on the epoxy specimen surface was quantitatively evaluated by surface charge mapping. In addition, the effect of the subsequent discharges occurring in a heterocharge configuration above the inception voltage was observed. In terms of their directions and lengths, the kinetics of the streamer filaments revealed a strong dependence on both the polarity and the intensity of an accumulated charge. Compared with the reference charge-free surface, the strongest drop in dielectric strength in the interelectrode space with a sprinkled charge was obtained for the heterocharge configuration. The presented results provide a contribution to the assessment of streamer behaviour in the presence of accumulated surface charges, including its polarity and intensity.