The Fire-Safe Insulating Oils for Power Transformers: A Critical Review

With the rapid progress of global urbanization, enhancing the fire safety of power transformers has become increasingly crucial. A primary cause of transformer fires and explosions is the ignition of insulating oil due to transformer leakage, short circuit, high temperature and other failures. To reduce fire risks, transformers typically use high fire point insulating oils or non-flammable oils instead of conventional mineral oils. However, comprehensive research on high fire safety insulating oils for power transformers remains in its early stages globally. From an energy security perspective, this paper conducts an in-depth analysis of the fire characteristics of oil-immersed transformers, demonstrating that substituting conventional mineral oil with high fire-safety insulating oils can significantly mitigate transformer fire risks. From an energy security perspective, this paper analyzes the fire characteristics of oil-immersed transformers in depth, demonstrating that the replacement of conventional mineral oil by high fire-safety insulating oil can effectively reduce the risk of transformer fires. Furthermore, a systematic review of global advances was conducted by analyzing recent publications, focusing on high fire-safety insulating oils for transformers, specifically synthetic esters, natural esters, and flame-retardant transformer oils. Based on a systematic review of the performance of various high fire-safety insulating oils, this paper summarizes their respective advantages and limitations. Synthetic and natural ester insulating oils exhibit excellent insulation properties and high fire points. However, their relatively high viscosity and insufficient stability somewhat impair heat dissipation efficiency and long-term service life. In contrast, flame-retardant mineral oils retain the favorable physicochemical properties of conventional mineral oils, yet face the challenge of balancing flame retardancy with insulation performance. Finally, prospective research directions and critical priorities are proposed for each category of high fire-safety insulating oils, offering actionable recommendations to guide future investigation and development efforts.