Redmond, J. and Bott, F., "Development of Cryogenic Electric Motors," SAE Technical Paper 640023, 1964, doi:10.4271/640023.
This paper describes the results of testing a-c and d-c electric motors operating while submerged in, and with internal parts wetted by, liquid hydrogen and nitrogen. The influence of cryogenic operation on the electrical and mechanical design is discussed, as well as general application considerations for motors cooled by several cryogenic fluids and gases. The results obtained from the test program undertaken prove that cryogenically cooled motors are not only feasible, but offer distinct motor and system advantages as compared to conventionally cooled motors. These advantages are higher horsepower per pound, increased efficiency, and system simplification. Further development of magnetic circuit configuration and copper-to-iron ratio is suggested for additional improvement.