Application of and operating experience with hydrogen-cooled synchronous condensers and alternators

TLDR: The only cooling medium utilized for electrical rotating machinery was air as mentioned in this paper, and this was not due to the fact that air has any particularly suitable characteristics but because it is the daily common surrounding medium which, of necessity, must be used for open-type machinery.

Abstract: UNTIL about ten years ago the only cooling medium utilized for electrical rotating machinery was air. Obviously this was occasioned not by the fact that air has any particularly suitable characteristics but because it is the daily common surrounding medium which, of necessity, must be used for open-type machinery. Before that time, the need for construction of machines of constantly increasing size and speed had brought about the development of closed systems of ventilating. In these, facilities had been provided for conditioning the cooling air, but this had been primarily for the purpose of removing dust particles. The elimination of the particularly objectionable oxygen had not been attempted although for some time inert gas had been used in transformers to prevent oxidation of oil or insulation.