Concepts of Static vs. Dynamic Current Transfer Length in 2G HTS coated conductors with a Current Flow Diverter Architecture

TL;DR

This study investigates static and dynamic current transfer lengths in 2G HTS coated conductors with a current flow diverter, revealing that dynamic CTL is larger and more relevant during normal zone propagation.

Contribution

Introduces the concept of dynamic CTL ($_d$), demonstrating its importance over static CTL ($_s$) in understanding current transfer during quenches.

Findings

Dynamic CTL ($_d$) is larger than static CTL ($_s$) in CFD architectures.

Normal zone propagation velocity is proportional to $_d$, not $_s$.

Shape of the normal zone influences the difference between static and dynamic CTL.

Abstract

This paper uses both experimental and numerical approaches to revisit the concept of current transfer length (CTL) in second-generation high-temperature superconductor coated conductors with a current flow diverter (CFD) architecture. The CFD architecture has been implemented on eight commercial coated conductors samples from THEVA. In order to measure the 2-D current distribution in the silver stabilizer layer of the samples, we first used a custom-made array of 120 voltage taps to measure the surface potential distribution. Then, the so-called "static" CTL ($\lambda_s$) was extracted using a semi-analytical model that fitted well the experimental data. As defined in this paper, the static CTL on a 2-D domain is a generalization of the definition commonly used in literature. In addition, we used a 3-D finite element model to simulate the normal zone propagation in our CFD samples, in order to quantify their "dynamic" CTL ($\lambda_d$), a new concept introduced in this paper and defined as the CTL observed during the propagation of a quenched region. The results show that, for a CFD architecture, $\lambda_d$ is always larger than $\lambda_s$, whereas $\lambda_d = \lambda_s$ when the interfacial resistance between the stabilizer and the superconductor layers is the same everywhere. We proved that the cause of these different behaviors is related to the shape of the normal zone, which is curved for the CFD architecture, and rectangular otherwise. Finally, we showed that the NZPV is proportional to $\lambda_d$, not with $\lambda_s$, which suggests that the dynamic CTL $\lambda_d$ is the most general definition of the CTL and should always be used when current crowding and non-uniform heat generation occurs around a normal zone.