International Round-Robin Test of Critical Current of Superconducting Cable Sample

Ten institutes from six countries participated in an international round-robin test to evaluate the critical current of a superconducting power cable made of Bi-2223 tapes. The cable design featured a two-layer inner core conductor and a single-layer outer shield conductor. The shield layer measured approximately 40 mm in diameter, and the cable length was 2.0 m. To eliminate the influence of resistive voltage drops from current transfer, voltage taps for measurement were positioned at a sufficient distance from the current terminals. The critical current was determined using the resistive method with the electric field criterion of 1.0 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\rm{\mu V}}/\text{cm}$</tex-math></inline-formula>. In addition, the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$n$</tex-math></inline-formula>-value, an optional parameter reflecting the current–voltage (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$I$</tex-math></inline-formula>–<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$V$</tex-math></inline-formula>) characteristics, was extracted from the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$I$</tex-math></inline-formula>–<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$V$</tex-math></inline-formula> curve within an electric field range of 0.1–1.0 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\rm{\mu V}}/\text{cm}$</tex-math></inline-formula>. A detailed uncertainty analysis was conducted for both the critical current and the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$n$</tex-math></inline-formula>-value. Finally, this article discusses the potential for standardization of the employed resistive measurement method.