Investigation of the effect of non-uniform stress distribution on the transient electromagnetic behavior of a no-insulation REBCO racetrack coil

Racetrack superconducting coils are widely used in magnetic levitation (maglev), generators, and accelerators, showing very important application prospects in many fields. However, due to the special geometry, the straight part and the arc part of the coil are given different radial stresses during the winding, cooling, and excitation, which will cause a difference in their transient performance during charging/discharging. In this paper, we investigated the transient electromagnetic behavior of the no-insulation (NI) REBCO racetrack coil during charging/discharging. First, an equivalent circuit model of a NI racetrack pancake (RP) coil was established. The stress distribution calculated by the analytical and finite element methods was used to consider the difference in contact resistance, the model can predict the current distribution of the straight and arc parts of different turns of the coil during charging/discharging. Afterward, A small-scale NI RP coil was successfully wound to validate the model, and the calculation results show good consistency with the experimental results. Finally, we investigated the transient behavior of the NI RP coil under different stress distributions. A targeted charging protection strategy for the coil was proposed and its effectiveness was verified experimentally. The work in this paper can help us to better understand the transient behavior of different parts of the NI RP coil during charging/discharging and provide guidance for its future construction.