AC Loss Characteristics of High-Temperature Superconducting Tapes Under Over-Current Conditions

The transport current of high-temperature superconducting tapes depends on the critical current value. The upper limit of the transport current is determined by the ratio of the load to the critical current value. In general, direct current must not be regularly energized above the critical current. However, unforeseen events or accidents may result in instantaneous over-currents. This test could be conducted under sufficient cooling; however, the temperature increase causes the critical current value to decrease. Consequently, the loss increases rapidly, resulting in superconducting tape burning out. Conversely, burnout can be prevented under sufficient cooling. This study aimed to investigate the alternating current (AC) loss characteristics by experimentally applying AC above the critical current value of high-temperature superconducting tapes. ReBCO tapes with varying protective layer thicknesses and Bi2223/Ag tapes with different critical current values were subjected to immersion cooling in liquid nitrogen. The four-terminal method was employed to measure the flow of AC above the critical current value. Based on the findings, with adequate cooling, high-temperature superconducting tapes were stably energized even beyond the critical current value.