Advances in synchronous machines employing high temperature superconductors (HTS)

In last few years, a number of superconducting S rotating machines with High Temperature Superconducting (HTS) field windings have been demonstrated and several projects are currently transitioning to advanced development stages. This paper reviews the history of superconducting rotating machine development worldwide utilizing superconducting field windings both Low Temperature Superconductor (LTS) and HTS. Replacement of conventional copper field winding with a superconducting field winding yields rotating machines with superior performance, higher reliability and easier operation. Such synchronous machines with superconducting field windings have been in development since mid-sixties. Initially the field windings employed low temperature superconductors, which did not yield economically attractive devices due to small thermal margin of the field winding and complex rotor cooling system. The HTS provide much larger thermal margin and enable much simpler rotor cooling systems. This has provided a new impetus to development of such machines for Naval and commercial applications. HTS machines in rating from a few kilowatts to several megawatts have been demonstrated in US and Europe. Currently, large high-torque ship propulsion motor and large generator prototypes are under development and are expected to be commercially available in the next few years. Improved life, smaller size, less weight, and higher efficiency benefits are providing incentive for development of large HTS machines.