Effect of SiO2 Nanoparticle's Size and Doping Concentration on AC Breakdown Behavior of Insulating Oil-based Nanofluids

Insulating oil based nanofluids can effectively enhance the dielectric strength of insulating oil for their application in transformers. This work is performed to enhance the dielectric strength of synthetic ester (Midel 7131) and Mineral oil (Karamay #25) by using insulative SiO2 nanoparticles of two sizes (15nm & 50 nm) with four concentrations of 0.05 g/L, 0.2 g/L, 0.3 g/L, and 0.4 g/L. The AC breakdown voltages of SE-based nanofluids increase with increasing the doping concentration. Moreover, SiO2 (15nm) exhibits better dielectric strength due to the accumulation of charges at the liquid-solid interface. However, the AC breakdown voltage of mineral oil (MO) based nanofluids of both nanoparticle sizes first increases to a certain extent and then decreases with further increasing the doping concentration. This might be due to the small average distance of nanoparticles at higher doping concentrations. Furthermore, the AC breakdown voltage and increment percentage compared to pure oil at 1%, 10%, and 50% breakdown probabilities for SE and MO-based nanofluids were studied from Weibull probability distribution curves. Consequently, the variation in the breakdown voltage of nanofluids depends upon nanoparticles' size, doping concentration, and nature of nanoparticles (NPs).