Thermal and electrical properties of thermal-grease-insulated REBCO superconducting coils with respect to winding tension

This study investigates the thermal and electrical characteristics of a silicon-based grease insulation (GI) GdBCO coil with respect to the winding tension through charge, sudden discharge, and over-current tests. Charge and sudden discharge test results demonstrate that the charging/discharging delay time increases as the winding tension increases; this is because the characteristic resistance of the coil decreases due to the reduced contact resistance. The over-current test results confirm that the thermal/electrical stabilities of the GI coil are considerably enhanced with an increased winding tension resulting from improved thermal contact and the decrease in the electrical contact resistance between the turn-to-turn layers of the coil. Thus, as the winding tension increases, the charging/discharging rates decrease whereas the thermal/electrical stabilities improve. Overall, selecting the appropriate winding tension for a GI coil is critical for achieving thermal/electrical stabilities, as well as ameliorating the charging/discharging delay phenomenon generally observed in a no-insulation coil.