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.