Critical Current Measurement in Three-in-One High-Temperature Superconducting Cables

This paper discusses the measurement of critical current I-C in three-in-one high-temperature superconducting (iHTS) cables. It is difficult to measure the I-C of long-length HTS cables by simply connecting a dc power supply to both ends of a single cable core. We propose a go-and-return method, in which the HTS conductor layers of two of the three cores are used to carry current in both directions. A current in the opposite direction is induced in the HTS shield layers. However, the current induction is less than that from ac transmission, and magnetic field leaks from each core. As a result, the measured I-C value becomes smaller than the sum of the wires' I-C. We used a transient electromagnetic simulation, taking into account the I-C-B characteristics of the wires. The estimated I-V waveforms for the 30- and 240-m cable systems are comparable with the measured ones. We have established a practical I-C measuring technique that can be used with long-length HTS cable.