VEGETABLE DIELECTRIC FLUIDS DOPED WITH TiO₂ PARTICLES FOR IMPROVED ELECTRICAL INSULATION AND THERMAL MANAGEMENT IN POWER TRANSFORMERS

The development of sustainable insulating materials is a key challenge in modern electrical energy systems, particularly in power transformers, where dielectric fluids play a critical role in electrical insulation and heat dissipation. In this work, vegetable-based dielectric fluids were developed through the incorporation of TiO₂ particles into a natural ester insulating oil matrix. Particles were synthesized using sol-gel route and characterized by X-ray diffraction and scanning electron microscopy. TiO₂ particle micrographs showed micrometric particle size (~1 µm) with a homogeneous dispersion. Fluids were prepared at concentrations of 0.1, 0.3 and 0.5 wt.% using controlled magnetic stirring and ultrasonic dispersion under constant temperature and low-humidity conditions to ensure homogeneous distribution of the particles. The resulting systems were evaluated in terms of rheological, thermal, and electrical properties. The vegetable base oil exhibited Newtonian behavior with a viscosity of approximately 58 mPa·s at room temperature. Rheological analyses for fluids confirmed that the addition of TiO₂ particles preserved the liquid-like behavior of the fluid at concentrations up to 0.5 wt.%. Overall, thermal analysis showed good structural and viscosity stability (60 mPa·s) in a temperature range of 20 - 200 °C for all fluids doped with particles. In contrast, the neat vegetable oil showed a viscosity increase (100 mPa·s) at 80 – 100 °C, and a sudden viscosity drop. Electrical tests following ASTM D1816 demonstrated a significant improvement in dielectric performance as a function of particle concentration, where the breakdown voltage increased from 22.9 kV for the base oil to 46.6 kV for the fluid containing 0.1 wt.% TiO_2,.34.3 kV for 0.3 wt.% and 28.1 kV with 0.5 wt.%. These results demonstrate that particle-modified vegetable dielectric fluids represent a promising strategy for developing environmentally friendly insulating media with enhanced electrical and thermal performance for next-generation power transformers.