Investigation of partial discharge mechanisms in a void under AC electric stress

In order to understand and predict the ageing of insulation which is subject to partial discharges (PD), it is necessary to investigate and understand the processes which occur in voids in the insulation. Only then can the effect on the insulation of the localised gas discharges which constitute the PDs be understood and characterised and used to determine insulation deterioration and hence ageing. To study such discharges requires determination of the actual discharge current waveform and as these have typical frequencies in the GHz region, measurement is not easy. This paper outlines a measurement system and gives results of PD currents measured in a model of a void in a solid insulation system. This work is part of a larger program of work aimed at developing a theoretical model of the discharge processes and using experimental data to fine-tune the model. Some details of the theoretical model analysis are also presented