Superconducting magnetic energy storage (SMES) has the ad-vantages of high efficiency, longevity, and excellent instantaneous response with high power. However, it has the disadvantage of having a very low energy storage density in comparison to other power storage devices. The no-insulation coil (NI coil) is expected to be a winding method capable of achieving both high current density and high thermal stability. It is predicted that if this NI coil technology can be used for SMES, it will be possible to improve energy storage density by achieving higher current density. Because the SMES is a power device, it is generally preferred for coils to be designed with high current and low inductance. Therefore, in this study, we considered adopting the winding method in which a bundle conductor using of multiple no-insulation REBCO tapes is wound without electrical insulation (hereinafter referred to as bundle NI coil) for SMES coils. However, because the REBCO tapes in the bundle conductors are not electrically insulated from one another and the bundles also have no electrical insulation between one another, the time variation of the current distribution in the bundle NI coil be-comes extremely complicated. Therefore, we developed a computer program that analyzes and evaluates the current distribution in a bundle NI coil, and for application to SMES, we numerically investigated the behavior during charge and discharge of a coil wound with a no-insulation bundle REBCO conductor. Furthermore, a small bundle NI coil was constructed and tested to confirm the validity of the developed computer program, and the time variation of the current distribution in the bundle conductor was based on the analysis results. In addition, the effect of the NI bundle coil on the storage efficiency when used to SMES was investigated experimentally and numerically.
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