Characteristics of liquid dielectrics

Liquid dielectrics are used in many applications (electrical engineering, power electronics, semiconductor industry, EDM machining, etc.) to perform a range of functions: electrical insulation, cooling, arc extinguishing, elimination of partial discharges, lubrication, and so on. For example, electrical and electronic equipment cannot operate without energy losses, which leads to a rise in the temperature of their constituent parts; this in turn necessitates cooling to achieve thermal equilibrium (resulting from the energy involved and the evacuation of losses), compatible with a normal service life for the equipment; liquids allow this, but must also ensure the electrical insulation of live conductors. Electrical insulation is very often provided in conjunction with solid insulating materials, in the form of impregnated insulation. Consequently, liquids must be compatible with solid insulators (paper, cardboard, polymers) as well as with construction materials (metals, plastics). The liquids used must therefore have specific electrical, physical and chemical properties, as well as the lowest possible toxicity to people and the environment. Obviously, a given liquid cannot have all the properties required, and these are often contradictory. So, depending on the application, and therefore its specifications, a compromise will have to be found.