Evaluation of Effectiveness of Strand Transposition in Multi-Stacked Coils Wound With No-Insulation Bundle REBCO Conductor for SMES

We have been developing no-insulation (NI) REBCO coil system for its application in superconducting magnetic energy storage (SMES). SMES has the advantages of high efficiency, long life, and the ability to respond to large amounts of power instantaneously. However, SMES has an extremely low energy storage density. To address this issue, the use of NI-REBCO coils, designed to achieve both high thermal stability and high current density, is expected to enable the realization of high storage density in SMES. In addition, since SMES is a power device, high current and low inductance design is desired. Therefore, we focused on the use of a REBCO coil system composed of four pancake coils wound by assembling four electrically uninsulated REBCO tapes (strands) into a laminated bundle conductor (hereinafter referred to as bundle NI coils). However, within bundle NI coils, the inductance of each strand varies, leading to un-equal current sharing and intricate current distribution. In this study, we developed a numerical simulation program to elucidate the behavior of current change in the bundle NI coils assuming SMES operations, and the program was used for analytical evaluation of current distribution in bundle NI coils.