HIgh Voltage Insulators: Liquids
Oil is commonly used in high voltage transformers and high power systems due to its excellent thermal conductivity, which can be improved further by circulation. Handling oil can be messy, and there can be environmental regulations to deal with if large quantities are used. One common type is manufactured by Shell.
Silicone oil is another good liquid insulator. In addition, silicone heat transfer fluids such as Dow Corning Syltherm™ can also be used as high voltage insulators.
Perfluorinated liquids such as Fluorinert™ are clean and easy to use. They are great insulators and can be used for testing high voltage circuits before they are potted. However, they are expensive, some types evaporate quickly.