The ongoing pursuit of enhanced efficiency and sustainability in power transformer cooling systems has spurred extensive research into the properties and performance of insulating fluids. This review explores the evolution of transformer cooling technologies, focusing on traditional mineral oils and the emerging roles of alternative fluids, such as natural and synthetic esters, and nanofluids. Mineral oils, though widely used, degrade over time, leading to a reduction in breakdown voltage (BDV) from 46 kV to 30 kV, exhibiting low fire resistance. Natural and synthetic esters provide improved biodegradability, fire safety but have higher viscosities—potentially limiting convective cooling. Nanofluids, have demonstrated BDV enhancements of up to 47.8%, reaching 88.7 kV in optimised formulations, alongside increases in partial discharge inception voltage (PDIV) of 20–23%. Additionally, thermal conductivity improvements of 5–20% contribute to enhanced heat dissipation. Moreover, it addresses challenges such as nanoparticle agglomeration, sedimentation, ageing, and compatibility with transformer materials. The analysis provides critical insights into the trade-offs between technical performance and economic feasibility. Concluding with an outlook on future research directions, the review identifies key parameters across various categories, establishing a roadmap for nanofluid integration with existing transformer systems.

Efficient cooling technologies for power transformers are critical to modern power systems, ensuring reliability, performance, and AN extended lifespan. This review systematically analyses advancements, challenges, and opportunities in cooling systems for power transformers. Oil-immersed transformers, widely used due to their superior insulation and effective cooling, require efficient thermal management to prevent overheating and ensure operational stability. This review evaluates key cooling strategies across oil-natural air-natural (ONAN), oil-natural air-forced (ONAF), oil-directed air-forced (ODAF), and oil-forced air-forced (OFAF) systems. It highlights innovations in radiator design, such as top-mounted radiators and chimney caps, and explores sustainable alternatives, including biodegradable esters, nanofluids, and hybrid ventilation methods. Advanced computational tools like Computational Fluid Dynamics (CFD) and artificial intelligence (AI), particularly neural networks, are identified as transformative for optimising cooling performance, predicting thermal behaviour, and enabling real-time monitoring. Despite progresses, challenges persist in radiator optimisation, airflow dynamics, and scalability of innovative cooling methods. By offering a comprehensive review and identifying critical areas for improvement, this study provides a foundation for developing cost-effective, reliable, and environmentally sustainable cooling systems, aligning with the growing demand for efficient energy infrastructure.