Development of Mixed Insulation Oil as Alternative Liquid Dielectric: A Review

Use of traditional mineral oil (MO) as a liquid insulation in transformers has spanned more than 130 years. However, MO has poor heat resistance, a low ignition point, and is a non-renewable resource, which does not meet development requirements for high-performance and environmentally friendly insulation oil. Consequently, researchers have explored alternatives such as natural ester (NE) and synthetic ester (SE) oils, as well as mixed insulation oils. Mixed insulating oil is a blend of diverse insulating oil types, with optimal performance achieved by adjusting proportions of base oils. This article summarizes the innovative achievements and development of mixed insulation oil in terms of development of mixed ratio, basic physical chemical properties, electrical properties, thermal stability, and application including operation and maintenance technology. Through these efforts, this article aims to provide recommendations for future development of mixed insulating oils to advance liquid dielectric research based on enhancement mechanisms.