Abstract: A transformer has a vertical winding assembly formed of a stack of pancake coils sandwiched between electrically insulating bases each provided on its surface contacted by an associated one of pancake coils with a plurality of cooling grooves extending in spaced relationship along turns of a rectangular electrically conductive wire forming the pancake coil and opening on the upper and lower portions of the base. A liquid refrigerant sprinkled on the winding assembly is arranged to flow through the cooling grooves via the upper open ends and be discharged via the lower open ends.

Abstract: The invention is relative with a gas-insulated electrical apparatus comprising a tank housing an electrical apparatus proper and in which a gas mixture consisting of a noncondensable insulating gas and a condensable refrigerant gas and a liquid phase of the condensable refrigerant gas are sealed, and a gas reservoir connected to said tank in the gas mixture feeding or receiving relation therewith. According to the invention, means are provided between the tank and the gas reservoir for selectively supplying said gas mixture from said tank into said gas reservoir or vice versa.