Characterisation of PD occurring in injected air bubbles in block polymeric insulation

Gas filled cavities in solid insulation can form during production and are likely to have initial spherical or ellipsoidal geometry; as degradation takes place the shape will distort. Due to the difficulties of producing spherical and ellipsoidal cavity shapes most previous partial discharge (PD) measurements, in polymeric insulations, have used a layered polymer sandwich approach to create flat cylindrical voids. A series of experiments is carried out on air bubble voids inside block polymeric insulation. This paper will investigate and compare the PD repetition rate, PD magnitude, PD distribution plots and the total charge injection in each void for samples with varying sizes of the air bubble. The PD characteristics recorded from these air bubble arrangements will also be compared to those obtained from layered polymer models of similar dimensions. Comparison of the natural and layered void results will provide information on validity of sample production methods.