Circuit Model of Interlayer and Screening Currents in Layer-Wound NI HTS Coils

In recent years the advent of the no-insulation high-temperature superconducting (NI-HTS) coils technology, has increased the need for new simulation tools to accurately predict their response in typical operating conditions. Detailed knowledge of the current distribution in NI-HTS coils is essential to compute the magnetic field profile generated by the coil, and investigate the losses in electrodynamic transient. Of the many circuit models proposed in the literature, few can describe the behavior of both the screening currents in the tape and the radial currents. This work aims to provide all the elements to create a lumped parameter circuit model suitable for an in-depth analysis of the current distribution inside a NI-HTS coil. The lumped parameters circuit model proposed in this work can compute the current distribution in both the radial and azimuthal directions inside the coil as well as the screening currents arising inside the REBCO tapes. To compute the distribution of the screening currents and their impact on AC losses, the tape composing each turn is discretized across its width with several sub-elements, each represented through different circuit components The model was compared with 2D FEM simulation and an analytical formula to asses its ability in evaluating the screening currents in the case of a single tape. Although this work is aimed at the study of layer wound NI-HTS coils, the model described can be applied to the study of tapes, stacks of tapes, or pancake coils just by modifying the topology of the network.