Classified effects of nanofillers on DC breakdown and partial discharge resistance of polypropylene/alumina nanocomposites

The enhancement of DC breakdown strength in polypropylene/alumina nanocomposites (NCs) with low filler content (1 wt%) while the obviously increased partial discharge (PD) resistance at higher filler content (15 and 20 wt%), are observed. Possible mechanisms underlying such contrastive performance are proposed based on considering a combination of electric conductivity, traps distribution and morphology of the eroded test specimen. The DC breakdown is closely related to trap-controlled charge transport and the property is improved for NCs with low filler content. Comparatively, the PD resistance of NCs with higher filler content exhibits longer failure time and more spreading of the eroded area on specimen surface. A model of PD resistance of NCs is proposed on the basis of synergistic effects of energy dissipation by nanoparticle scattering and charge dissipation. The scattering effect on charged ions induced by nanoparticles plays an important role in energy dissipation, and faster charge dissipation along the sample surface induced by shallower traps mitigates energy concentration. Thus two aspects contribute to the improved PD resistance. It is concluded that the effects of nanofillers on short-term DC breakdown and long-term PD resistance are different. A low filler content improves short-term DC breakdown performance whereas a high filler content enhances long-term PD resistance.