A Short-Circuit Experiment of High-Temperature Superconductor Tapes

Superconducting dc power transmission (SCDC) is one of the most potent transmission lines because it is a low-loss, low-voltage, and small-cable system. However, one of the present technical issues is the short-circuit current. Since the current density of the high-temperature superconducting (HTS) tape is ∼100 times higher than the copper and aluminum conductors in regular operation, it is more severe than the copper cables for the short-circuit current. We started the short-circuit experiments for a single HTS tape a few years ago. We constructed the capacitor bank to generate a short pulse current; its pulse duration is a few ms for the Bi2223 tape and ∼60 ms for the RE123 tape. Their peak currents are 10 to 30 times larger than the critical currents (
I
_c
) of the HTS tapes. We measure the
I
_c
at the first step and flow the pulse current in the next step, and finally, we measure the
I
_c
again if we can measure the
I
_c
. If the
I
_c
after the pulse current is lower than the original, the pulse current degrades the HTS tape. These are the ways of the experiments. We use RE123 tape; its initial
I
_c
is 200 A, the pulse duration is ∼60 ms, and the peak current is above 2.2 kA. After the pulse current, the
I
_c
was almost identical to the original. However, if the peak current exceeded 2.4 kA, we observed the arc in the tape, and it broke the RE123 tape, or the critical current was lower than the original. We also tested the Bi2223 tape, which is more robust than the RE123 tape. At the same time, we estimated the temperature of the HTS tape during the discharge, which was higher than 300 degrees Celsius, even in liquid nitrogen (LN2), because the voltage-tap solder was molten. These experimental results are the basis for designing the HTS power cable.