Development of a submerged winding induction generator for cryogenic applications

This paper discusses the development of a series of one-megawatt, 3.3 kV variable speed input, constant frequency output induction generators to be used while totally submerged in liquid methane at -161°C. The specific purpose and application of these induction generators was to increase the overall efficiency of a gas liquefaction plant by replacing all inline Joule-Thomson expansion valves with cryogenic turbine generators and, as a by-product of this replacement, the cogeneration of electric power. Areas of concern during the development of the generators included optimization of the generator´s voltage to maximize system life and efficiency, the impact of high-speed switching IGBTs on wire and ground insulation, the magnitude and effects of partial discharge in a cryogenic liquid environment and the compatibility of insulation materials to hydrocarbon based fluids at cryogenic temperatures