1. Mineral oils

The use of mineral oils in electrical equipment dates back almost to the beginning of industrial production. They have two main functions: electrical insulation and heat transfer.

Mineral insulating oils are obtained by distillation of selected petroleum products, natural substances of geological origin, stripped of various materials (light gases, hydrogen sulfide, water, etc.). They are complex mixtures (several thousand different molecules) of hydrocarbons, sulfur compounds, oxygenates, nitrogen compounds and traces of organometallic compounds. They are known as crudes. They are extracted in all regions of the world, and several hundred different types have been identified.

Progressive improvements in crude oil refining processes have led to the production of increasingly high-performance mineral insulating oils. These improvements, combined...