A Simple Method to Estimate Coil Temperature With Local Normal-State Region

This paper proposes a simple analytical expression to estimate the temperature of no-insulation (NI) high-temperature superconducting (HTS) coils when a local normal zone appears. The combination of the NI winding technology and HTS, especially rare-earth barium copper oxide (REBCO), enables high-field generation with high thermal stability. Since the advent of the NI winding technology, a few simulation techniques have been improved: the finite element method (FEM) and the partial element equivalent circuit (PEEC) are well-established as of today. The PEEC method can simulate the coil behaviors relatively fast compared with the FEM simulation due to the number of elements. However, the computation time is still long, particularly when a normal-state transition is simulated coupled with thermal analysis due to the extreme non-linearity of the superconductors. Therefore, we have previously proposed a simple and versatile analytical expression to estimate NI HTS coil temperatures in the cases of ramping down with an arbitrary speed and sudden discharging. Compared with PEEC simulations, the analytical formulae were validated in both cases under the assumption that the NI HTS coil is perfectly superconducting. In this paper, taking further realistic considerations into account, an NI HTS coil with a few normal-state turns is modeled, and its temperature is also formulated. The calculation results are validated with the PEEC model, and the accuracy and usable range of the proposed method is also discussed.