High-performance superconducting windings for AC generators

Superconducting windings are susceptible to mechanical instabilities that degrade their performance. The problem, often referred to as training, results from, wire motion. A technical approach is presented to develop superconducting rotor windings for large generators that are capable of attaining the theoretical maximum current density of the superconductor without training. The winding is assembled from racetrack-shaped, epoxy-impregnated modules, Epoxy impregnation is used to restrict wire motion and frictional heating within the winding. A support structure is shrunk around the winding modules to provide support of the winding against centrifugal and magnetic forces, and restrict sliding movement of the winding relative to the support. Further, a winding interface material is employed to enhance friction so that compression at the winding interface results in frictional forces that are larger than the shear forces. Thus, sliding motion can be prevented. A model superconducting rotor for a 20 MVA generator has been developed according to this technique to simulate the winding electromagnetic loading and interface parameters. The winding was tested statically in a bath of liquid helium. It attained the theoretical maximum current repeatedly without training. The experiments have validated the analytical predictions.