Experimental Study on Thermal Behavior of HTS Coils with Quasi-Insulation Winding Method at Overcurrent Operation

Recently, superconducting power applications by using the high-temperature superconducting (HTS) tape have been widely researched due to the development of the HTS tape. In particular, the HTS coils cowound with insulation materials have been dominantly used for the power applications. However, the insulated HTS coil has low thermal stability at overcurrent operation, which causes much likely to be damaged. To relieve this issue, other insulation methods such as insulation-free or partial insulation have been investigated. These methods have good thermal stability; however, they have weaknesses such as magnetic field saturation and charge-discharge delay as well. In particular, charge-discharge delay is a significant obstacle for superconducting magnetic energy storage due to a frequently variable current operation. Therefore, a quasi-insulation (QI) coil that compensates the disadvantages has been proposed. In this paper, two QI coils according to the width of the insulation tape were fabricated since the performance of this winding method is affected by the exposure area to the coolant. In addition, insulation-free coil and partial insulation coil were fabricated and tested as the control group. The terminal coil voltage and center magnetic field were measured to compare the characteristics of each coil. The experimental result shows the QI coil has good thermal stability at overcurrent operation without magnetic field saturation and degradation. In addition, cooling effect is proportional to the exposed area to the coolant and adjustable with a different width of insulation tape.