A liquid dielectric is a dielectric material in liquid state. Its main purpose is to prevent or rapidly quench electric discharges. Dielectric liquids are used as electrical insulators in high voltage applications, e.g. transformers, capacitors, high voltage cables, and switchgear (namely high voltage switchgear). Its function is to provide electrical insulation, suppress corona and arcing, and to serve as a coolant.
A good liquid dielectric should have high dielectric strength, high thermal stability and inertness against the construction materials used, non-flammability and low toxicity, good heat transfer properties, and low cost.