Stability of epoxy-impregnated AC superconducting winding

AC superconducting composite wires for 50-60 Hz application are very susceptible to disturbances due to wire motions, because matrices of the wires are highly resistive CuNi. Instability of the wires is one of the most serious problems in developing AC wires of large current capacity. An effective technique to reduce the wire motions is to impregnate the windings. The authors demonstrate that the stability was much improved by the impregnation, and that the AC losses could be cooled by the heat conduction through the epoxy without significant wire-temperature rise, provided that the thickness of the epoxy-impregnated layer was adequately small. In the paper, effective thermal conductivity of the epoxy-impregnates are investigated experimentally and theoretically. The characteristics of epoxy-impregnated 100 kVA class AC coils are compared to those of non-impregnated coils