Experimental study and numerical modelling of a dielectric barrier discharge in hybrid air–dielectric insulation

Results from experiments and numerical modelling of dielectric barrier discharges (or microdischarges) responsible for surface charging of a plane-parallel electrode arrangement covered with non-conducting solid dielectric coatings and comprising an air gap are presented. The purpose was to analyse the discharge progress and its influence on the surface charge build-up, which essentially is the cause of, from a high voltage insulation perspective, a beneficial electric field distribution with lowered electric field in the air gap and enhanced electric field in the dielectric coatings. The experimental investigation was performed in terms of high-voltage impulse testing, applying a crest voltage at the discharge inception level. Discharge current was measured and its progress in the air gap was photographed using an image intensified charged-couple device camera. Temporal and spatial development of an individual barrier discharge in a plane-parallel and rotational-symmetric geometry was numerically analysed by means of a two-dimensional diffusive-drift model. The idea of using limited barrier discharging to condition the hybrid insulation, which changes the electric field distribution and subsequently improves the insulation performance of the electrode system, is effectively demonstrated by the numerical simulation and supported by measured results. In a number of cases, measured and calculated discharge current patterns were found to agree structurally and to correctly display the predicted avalanche and streamer discharge phases.