Statistical Investigation of AC Dielectric Strength of Natural Ester Oil-Based Fe 3 O 4 , Al 2 O 3 , and SiO 2 Nano-Fluids

This paper deals with the effects of conductive and insulating nanoparticles at various sizes and concentrations on the ac dielectric strength of natural ester oil, namely, MIDEL 1204. The investigated nanoparticles are conductive (Fe3O4) and two insulating (Al2O3and SiO2). The measurements of breakdown voltages are achieved according to IEC 60156 standard. Experimental findings show that the investigated nanoparticles have not a significant influence on insulation performances of natural ester oil as it is the case with mineral oils and synthetic esters. The best improvement does not exceed 7%; it is obtained with Fe3O4(50nm) at a concentration of 0.4 g/L and Al2O3(13 nm) at a concentration of 0.05 g/L. In some cases, the addition of nanoparticles even reduces the dielectric strength of natural ester oil. Indeed, a decrease of 15% is observed with SiO2at a concentration of 0.05 g/L. The statistical analysis of experimental results is performed using two probabilistic functions, namely, normal and Weibull laws. It is shown that the breakdown voltage values of the investigated nano-liquids generally obey the normal and Weibull distributions. In addition, the breakdown voltage with a risk of 1% and 50% probability is deduced.