Sol–gel synthesis of copper oxide nanoparticles for the enhancement of transformer oil insulation strength

The growing demand for improved dielectric fluids in high-voltage electrical equipment has led to significant interest in nanoparticle-enhanced transformer oils. While various metal oxide nanoparticles such as Al₂O₃, TiO₂, and SiO₂ have been studied, limited research has focused on copper oxide (CuO) nanoparticles synthesized via the sol–gel route—an approach that offers superior control over particle size, purity, and morphology. This study aims to fill that gap by investigating the effects of sol–gel-derived CuO nanoparticles on the dielectric and thermal performance of transformer-grade mineral oil. CuO nanoparticles with crystallite sizes ranging from 20 to 50 nm were synthesized and characterized using X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM), confirming phase-pure monoclinic CuO. Nanofluids were formulated at three different concentrations (0.025, 0.05, and 0.075 wt%) and evaluated for AC breakdown voltage, viscosity, thermal conductivity, and fire safety characteristics. The results revealed a significant improvement in breakdown voltage, with a 29% increase observed at 0.075 wt% loading (from 60 to 77.4 kV), attributed to deep trap formation and interfacial polarization effects. Thermal conductivity improved with increasing CuO content, while viscosity decreased at elevated temperatures, enhancing convective heat transfer. Furthermore, the flash and fire points rose markedly, indicating improved thermal stability and fire safety. These findings demonstrate that sol–gel-derived CuO nanoparticles provide a synergistic enhancement of dielectric and thermal properties, offering a promising pathway toward next-generation, high-performance transformer oils.

Graphical Abstract