Role of nanofiller porosity in monitoring streamer and phonon dynamics in Transformer oil

This paper presents a maiden attempt to witness several nanofluidic properties of porous nanofillers dispersed in Transformer oil (TO). For this, Porous Boron Nitride (PBN)-PBN 950 and PBN 1050 at two different porosities with low (high) and high (low) specific surface area (SSA) and aspect ratio (AR) respectively, both composed of 2D porous flakes of quasi-crystalline BN of hexagonal phase, arranged in rod and flower pattern were obtained via gas-solid interaction at 950 and 1050oC respectively. Nanofluids of both PBNs in TO displayed a linear relationship between porosity and insulation characteristics with ~26-39 % rise in AC Breakdown Voltage along with Resistivity. It was explained by the role of nanofiller porosity in providing large interfacial zones and deep traps for quantitively scavenging and holding streamer charges at the oil-nanofiller interface. Further, despite of being quasi-crystalline and porous, both PBNs in TO upgraded the thermal properties by quasi-ballistic transfer of acoustic phonons via 2D flakes of hexagonal phase. However, the thermal conductivity varied inversely with porosity with ~ 32.5 - 28 % surge with PBN 950 and PBN 1050, respectively at 50oC. This trend was theoretically supported as well as explained due to the increase in phonon-defect scattering owing to the increase in porosity and pore asymmetry together with reduced AR in PBN 1050. Finally, the unchanged flash and pour points with negligible increase in acidity over months plus the aforementioned results at low filler fractions establishes the superiority of PBN over other BN nanofillers for applications in liquid insulation in future