Thermal Stability Analysis of a Conduction-cooled HTS Coil in AC Operations

Abstract

In our previous study, thermal runaway currents of a conduction-cooled single pancake coil wound with a Bi2223 tape wire were experimentally and numerically investigated and the relation between the cooling structure and the thermal runaway current was explained. On the basis of the results, we designed and fabricated a conduction-cooled HTS coil composed of 12 single-pancake coils and confirmed that the coil had a thermal stability as designed in DC operations. Secondly, the AC loss characteristics of the HTS coil were measured at 20-50 K and 0.05-2 Hz. Hysteresis losses of the coil were well explained using equations based on the Brandt model. As the result of the AC loss measurements, it was found that coupling losses were expressed as α(T)*(B_zf)². Adopting the functions of hysteresis losses and coupling losses into the thermal stability analysis program developed in our previous study, the thermal stability of the conduction-cooled HTS coil was numerically investigated. In this paper, the thermal stability analysis results are described.