Normal zone propagation in various REBCO tape architectures

Abstract

The normal zone propagation velocity (NZPV) of three families of REBCO tape architectures designed for superconducting fault current limiters (SFCLs) and to be used in high voltage direct current (HVDC) transmission systems has been measured experimentally in liquid nitrogen at atmospheric pressure. The measured NZPVs span more than three orders of magnitude depending on the tape architectures. Numerical simulations based on finite elements allowed to reproduce well the experiments. The dynamic current transfer length (CTL) extracted from the numerical simulations was found to be the dominating characteristic length determining the NZPV instead of the thermal diffusion length. We therefore propose a simple analytical model, whose key parameters are the dynamic CTL, the heat capacity and the resistive losses in the metallic layers, to calculate the NZPV.

A sulfurization method for creating the buffer-layers current flow diverter architecture in REBa2Cu3O7 coated conductors

“…Furthermore, the rise of the electric field is approximately 60 V m −1 s −1 which is 50 times higher than the pristine sample. This is consistent with NZPV measurements performed on theses samples, where it was found that the bCFD-sulfide sample had a NZPV 18 times higher than the pristine sample [15].…”

“…However, in our experimental setup, we reached the objective of partially sulfurized the silver without degrading the superconductor by exposing a tape for 3.5 h to the sulfur gas. Moreover, the expected quench performance associated with NZPV boost coming from the bCFD architecture previously demonstrated [15] was confirmed by DC limitation tests. The tests revealed that the voltage raised much faster with the bCFD-sulfide sample (60 V s −1 ) in comparison with the pristine sample (1.2 V s −1 ).…”

“…If the NZPV is slow (in the cm s −1 range) and the current in the conductor is not limited quickly enough, the local joule heating of the HTS resistive state in the hot spot is likely to irreversibly damage the tape [14], and even rupture the crosssection of the CC completely. Recently, an experimental study from Lacroix et al [15] comparing the NZPV at 77 K and selffield of different REBCO CC architectures mentioned a sulfurization technique capable of effectively creating the bufferlayers-CFD (bCFD) architecture (figure 1) which allowed to increase the NZPV by a factor of 18. In this paper, we describe this approach in further details.…”

“…dewetting) during heat treatments [29], like the final oxygen annealing process required for loading oxygen into the REBa 2 Cu 3 O 7−δ [30][31][32]. In [33], it has been shown that a 20 nm thick silver layer on top of YBCO forms spherical islands and becomes electrically discontinuous when annealed at temperatures as low as 300 • C. Therefore, the partial replacement of the Ag stabilizer with Ag 2 S to tune the effective stabilizer thickness on silver coated commercial CCs, come as a cheap and simple solution for implementing the bCFD [15]. Furthermore, there already exists extensive experience in scaling up the sulfurization processes in the fabrication of large area copper indium gallium sulfur (CIGS) solar cells and thus it is expected that it should be also feasible for Ag 2 S [34][35][36].…”

Some Results of the EU Project FASTGRID

“…Other strategies have been investigated by ICMAB during FASTGRID. The last and most promising is based on a silver sulfide insulating layer [20], whose industrial implementation is rather easy. This time, the CFD effect was clearly experimentally demonstrated.…”