Shaft-Mounted Cryogenic Refrigerator for HTS Motors and Generators

Due to their high-power density and efficiency, large-capacity, high-temperature, superconductor (HTS) motors and generators offer a number of advantages over conventional electrical machines for ship propulsion and power generating systems. One of the key practical issues with HTS machines is the ancillary support equipment required to accommodate the low cryogenic rotor operating temperature (~30 K). In particular, cryogenic refrigeration is problematic since available cryocoolers cannot be mounted on the HTS machine shaft, requiring the use of slip couplings to pass cryogenic helium to and from the shaft. The objective of the currently proposed Phase I SBIR project is to evaluate the potential of developing a shaft-mounted cryocooler to eliminate these couplings, as well as reduce the size and mass of the cryocooler. There are substantial constraints on size, weight, and reliability in this application that present significant challenges for most existing cryocooler technologies. Our approach is based on proprietary reverse-Brayton cryocooler technology, which will be unaffected by HTS machine rotation and should provide many other benefits such as ultra-high reliability, light weight, compactness, and flexible packaging. Our approach eliminates the need for an auxiliary cryogenic circulator and can be easily scaled across a broad range of HTS machine cooling requirements.