Preliminary study on AC superconducting machines

Issues involved in developing AC superconducting machines are reviewed with respect to the development of a superconducting coil and the overcurrent protection system of a superconducting transformer. A 4-kVA superconducting coil using 100-A-class 50/60-Hz superconductors was made and tested. As an extension of the 4 kVA coil, a model superconducting transformer was made and examined. The transformer has a novel quench-protection system with an auxiliary coil on the low-voltage side only. The behavior of the overcurrent protection system is described and experimentally confirmed.