Optimized Shape of Short-Circuited HTS Coils by Cutting Process for Superconducting Fault Current Limiters

Abstract

This article presents an optimization of short-circuited superconducting coils to be used in superconducting fault current limiter devices. The optimized shape reduces losses, eliminates overheating points, improves current distribution, uniforms the voltage drop over the tape length, and ensures uniform resistivity. The geometric analysis and its optimization are presented in this article. The results of computational simulation by finite element method are also presented. Superconducting tape cutting methods and coil welding are investigated. The influence of geometry and cutting technique on the critical current are evaluated based on the experimental tests results. Cutting high-temperature superconductor tapes by punching or laser process showed excellent results using <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\theta ={7.5}^{\circ }$</tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${30}^{\circ }$</tex-math></inline-formula> , where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\theta$</tex-math></inline-formula> is a characteristic angle of the geometry of the coil. There was no excessive degradation of the critical current or delamination, which is common due to the cutting. The laser process led to higher critical current values per unit width ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$I_c-{\rm mm}$</tex-math></inline-formula> ) to angle cut <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\theta ={30}^{\circ }$</tex-math></inline-formula> , a characteristic that has its origin in two factors: 1) temperature increase in a larger area when the adopted cutting angle is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${7.5}^{\circ }$</tex-math></inline-formula> and 2) higher cutting precision, which imposes a slightly different cross section when compared to the punching process.