Abstract
Synthetic esters are potential substitutes for mineral oil in power transformers owing to their biodegradability and excellent dielectric withstand. Furthermore, the addition of certain nanoparticles improves the cooling property of liquids. Both dielectric withstand and cooling are two fundamental characteristics for use in breathable components. Previous studies showed that AC breakdown voltage of synthetic ester could be increased by adding Fe 3 O 4 , Al 2 O 3 and SiO 2 nanoparticles. This paper deals with the DC breakdown voltage of the same synthetic ester-based nanofluids. Nanofluid samples are characterized using the same techniques to those used for AC breakdown voltage study. This includes a particle size analyzer, scanning electron microscope and energy dispersive x-ray spectroscopy analyzer. Statistical analysis of experimental data using normal and Weibull laws and an estimate of DC breakdown voltage with probabilities of risk of 1% and 50% are performed. The experimental results evidence the existence of an optimum concentration of nanoparticles that gives the highest DC breakdown voltage, except SiO 2 nanoparticles which degrade the DC breakdown voltage of pure synthetic ester, regardless of the concentration. For the other two types of nanoparticles, the DC breakdown voltage is improved by approximately 25%, 13%, and 10%, with Al 2 O 3 (13 nm), Al 2 O 3 (50 nm), and Fe 3 O 4 (50 nm) nanoparticles at the optimum concentration that is 0.05 g/L, respectively. It is also shown that the obtained results generally comply with the normal and Weibull distribution laws.