Superconducting magnetic energy storage (SMES) can provide high efficiency, longevity, and instantaneous response with high power. However, its energy storage density is extremely low. To address this drawback, the use of a no-insulation (NI) REBCO coil has been considered. NI coils are expected to achieve high current density as well as high thermal stability, and the energy storage density can be improved by applying these coils to SMES. However, Joule loss occurs owing to the current flow in the radial direction through the contact electrical resistance between turns during charging and discharging. Because the amount of loss depends on the contact electrical resistance, it is necessary to adjust the resistance to an appropriate value to make the storage efficiency a practical value. In this study, we conduct experiments to investigate the behavior of small-scale NI-REBCO coils with different contact electrical resistances considering the charge/discharge current pattern for actual SMES operation. In addition, numerical simulations are performed using the partial element equivalent circuit (PEEC) model under the same conditions as those used in the experiment, and the reproducibility of the experimental results is confirmed. Finally, using the PEEC model, numerical simulations are performed assuming an m-class coil. The relationship between the storage efficiency and the contact electrical resistance, which is an important indicator for applying NI coil technology to SMES, is clarified by the results.
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