Thermal and dielectric performance of transformer oil-based nanofluid with fullerene C60 nanoparticles

Contemporary distribution transformers face modern technological and integration challenges due to modern electrification and load increase. Motivated by the need for improvement of transformer safety, lifetime, thermal and dielectric performance, we carry out research on transformer oil-based nanofluid with fullerene C60 nanoparticles as a potential replacement for conventional transformer oil. Unlike numerous studies based on numerical or experimental investigation of thermal or dielectric properties, we provide a comprehensive research on C60 nanofluid in academic laboratories and in industry, complemented by an analytical modeling. Large-scale nano-functionalization of transformer oil is performed unconventionally by dissolving C60 powder using an industrial oil treatment machine under controlled temperature and oil pumping conditions. The prepared nanofluid is applied in a three phase 250 kVA distribution transformer, on which temperature rise and high voltage tests are conducted. The nanofluid is subjected to experimental investigation of key physical properties, like density, viscosity, nanoparticle concentration, thermal conductivity, flash point, dielectric breakdown, dissipation factor and permittivity. An analytical model of a natural convection loop is employed to predict the effects of adding C60 nanoparticles into the oil on temperature and flow velocity within the distribution transformer. It is found that very small C60 concentration (0.004% w/V) determined by spectrophotometry has a low or negligible impact on viscosity, density and thermal conductivity, while significantly increases AC breakdown voltage (by 65%) and decreases flash point of the oil. The transformer filled with the C60 nanofluid met the requirements of the standard EN 60076-2:2011. Comparison of transformer temperature rise tests and analytical model predictions show a slight decrease in the transformer temperature due to enhanced coupling between the windings and cooling surfaces through improved oil circulation. The collected experimental, numerical and industrial results provide pros and cons of the large-scale C60 nanofluid preparation and future application in distribution transformers.