Abstract: Electrical inductive apparatus cooled and electrically insulated by a vaporizable liquid dielectric having a boiling point within the normal operating temperature range of the apparatus. When the electrical inductive apparatus is at ambient temperature, the liquid dielectric completely fills the enclosure providing electrical insulation for the electrical members. As the temperature of the apparatus increases towards its normal operating range, the liquid dielectric is gradually withdrawn into a reservoir until, at the normal operating temperature, only a quantity of liquid dielectric sufficient to completely cover the electrical inductive apparatus remains in the enclosure. In response to a temperature decrease, the liquid stored in the reservoir is gradually returned to the enclosure thereby maintaining a constant level of dielectric strength between the electrical members.