Dielectric properties of aged mineral oil filled with TiO2 nanoparticles

When mineral oil is exposed to aging processes during their operation, oil properties significantly deteriorate. This necessitates reclamation of the oil or replacement with a new one. Both solutions are not preferred due to their high cost. From this viewpoint, this study aims to enhance aged oil properties by using nanofillers to be suitable for reusing in power transformers. Accelerated aging test is carried out through heating oil at 120 degrees C in an oven for different periods of days. Under this condition, accelerated aging for one day is considered to be equivalent to aging for one year in the field. Nanofluids are prepared by direct mixing of nanoparticles with degraded mineral oil. The considered nanoparticles in this study are titanium oxide nanoparticles. The breakdown voltage for prepared nanofluids are measured and compared to that of pure aged oil. Also, dielectric constant and dielectric dissipation factor have been measured. Nanofluids exhibited significant enhancement either in breakdown voltage or in dielectric dissipation factor. The physical mechanisms behind the obtained enhancement have been discussed considering the effect of aging and the role of nanofiller. It is found that nanoparticles alleviate the effect of moisture through adsorbing moisture species and forming hydroxyl groups around the surface of nanoparticles.