Functional dielectric nanofluids for transformer insulation: Interfacial engineering, thermal transport, and long-term stability

Reliable operation of electrical equipment hinges on the performance of insulating materials, which often fail under prolonged electrical, thermal, and environmental stresses. Nanotechnology offers a transformative solution: dispersing engineered nanoparticles in insulating liquids to create high-performance transformer nanofluids with enhanced dielectric and thermal properties. Therefore, this review systematically examines the synthesis, characterization, and performance of nanofluids containing insulating, conductive, and semiconductive nanoparticles, focusing on their effects on breakdown voltage, resistivity, thermal conductivity, and ageing. Furthermore, while numerous studies demonstrate that nanoparticles improve performance through interfacial polarization and electron trapping, critical relationships between particle concentration, size, surface functionalization, and the base liquid chemistry remain poorly understood, limiting practical adoption. Current research emphasizes material design, nanoparticle synthesis, and lab-scale stabilization. However, economic feasibility, long-term ageing, safety, toxicity, regulatory compliance, life-cycle assessment, and practical transformer integration are largely unexplored, representing key gaps for real-world deployment. By analyzing mineral and ester-based systems, this review identifies optimal nanoparticle loadings and emphasizes the non-linear dependence of dielectric performance on dispersion stability. These insights provide a framework for standardized nanofluid formation and testing, paving the way for next-generation, sustainable, and reliable transformer insulation technologies, while highlighting areas for future work to bridge laboratory innovation with industrial application.