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 and other shipboard HTS systems is the support equipment required to accommodate the required cryogenic operating temperature (~30 to 50 K). In particular, cryogenic refrigeration is problematic for HTS machines since available cryocoolers are bulky and cannot be mounted on the shaft, requiring the use of problematic cryogenic slip couplings. In Phase I, we evaluated the potential of Creare’s reverse-Brayton cryocooler technology to meet the need for cooling in large HTS machines and other shipboard HTS applications. We developed a system design and several conceptual layouts for integrating a reverse-Brayton cryocooler with a rotating HTS machine. We identified a number of advantages provided by the reverse-Brayton cryocooler including the ability to mount the cryocooler on the shaft of an HTS machine, the ability to eliminate separate cryogenic circulator(s), compactness, and extremely high reliability. The objective of the currently proposed Phase II effort is to develop the key components of a shipboard reverse-Brayton cryocooler, integrate them into a system, and demonstrate the overall performance.