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.

Second-generation (2G) superconducting wires have already proved their potential in several applications. These materials have a highly nonlinear behavior that turns an optimized engineering project into a challenge. Between several numerical techniques that can be used to perform this task, the integral equations (IE) method stands out for avoiding mesh problems by representing the 2G wire cross-sectional area by a line. While most applications need to be represented in a 3D geometry, the IE is limited to longitudinal or axisymmetric models. This work demonstrates that a complex 3D geometry can be modeled by several coupled simulations using the IE method. In order to prove this statement, the proposed technique was used to simulate a 2G racetrack coil considering the self-field magnitude (B) and incidence angle (θ) on the tape. The J c characteristic was modeled in terms of parallel and normal to the tape plane magnetic field components (J c (B P , B ⊥ )) obtained from a V-I(B, θ) characterization of a tape segment. This result was implemented using commercial software with both A-V (vector magnetic potential and scalar voltage potential) and IE coupled simulations solved by finite elements. This solution bypasses the meshing problem due to the tapes slim geometry, considering each turn a single 1D model, all magnetically interacting in two 2D models. The simulations results are in good agreement to what was both expected and observed in the literature. The simulation is compared to the measured V-I characteristic for a single pancake racetrack coil built with same geometry as its simulation models, and a theoretical study demonstrates the possibilities of the proposed tool for analyzing a racetrack coil current density and electric field behavior in each of its turns.

The primary benefit of a metallic stabilization/shunt in high temperature superconductor (HTS) coated conductors (CCs) is to prevent joule heating damage by providing an alternative path for the current flow during the HTS normal state transition (i.e., quench). However, the shunt presence in combination with unavoidable fluctuations in the critical current ( I c ) of the HTS film can develop a localized quench along the CC’s length if the operational current is kept close to I c . This scenario, also known as the hot-spot regime, can lead to the rupture of the CC if the local quench does not propagate fast enough. The current flow diverter (CFD) is the CC architecture concept that has proven to increase the conductor’s robustness against a hot-spot regime by simply boosting the quench velocity in the CC, which avoids the shunt compromise in some applications. This work investigates a practical manufacturing route for incorporating the CFD architecture in a reel-to-reel system via the preparation of yttrium oxide (Y 2 O 3 ) as an insulating thin nanolayer (∼100 nm) on top of a GdBa 2 Cu 3 O 7 (GdBCO) superconductor. Chemical solution deposition (CSD) using ink jet printing (IJP) is shown to be a suitable manufacturing approach. Two sequences of the experimental steps have been investigated, where oxygenation of the GdBCO layer is performed after or before the solution deposition and the Y 2 O 3 nanolayer thermal treatment formation step. A correlated analysis of the microstructure, in situ oxygenation kinetics, and superconducting properties of the Ag/Y 2 O 3 /GdBCO trilayer processed under different conditions shows that a new customized functional CC can be prepared. The successful achievement of the CFD effect in the case of the preoxygenated customized CC was confirmed by measuring the current transfer length, thus demonstrating the effectiveness of the CSD-IJP as a processing method.

Superconducting fault current limiters are very attractive devices which require to increase its robustness against the destructive hot spots. The use of sapphire substrates to grow YBa2Cu3O7 films is a very attractive approach due to its high thermal conductivity. This article reports the growth of microcrack-free, epitaxial YBa2Cu3O7(CZO) (YBCO)/YSZ/r-cut layers by Chemical Solution Deposition (CSD)barely polished sapphire substrates on Ce1-xZrxO2which can be produced in long lengths at low cost. The surface quality of the r-cut sapphire and its role on the epitaxy of CZO and YBCO layers is discussed. The issue of the microcrack generation in YBCO layers is investigated in relationship to the film thickness, the growth process and the oxygenation annealing step. We demonstrate that microcracks formation is related to the in-plane tensile stress generated during the oxygenation step instead of the differential thermal expansion effects and thus it can be minimized through an adapted oxygenation process. We have shown that CSD growth of YBCO films with thicknesses up to 400 nm and attractive superconducting properties (JC 1.9 MA/cm2 at 77 K) can be achieved on barely polished sapphire substrates which can be used at moderate cost for SFCL devices.

We investigated the integration of transient liquid-assisted growth (TLAG) approach for epitaxial YBa2Cu3O7-x (YBCO) films by physical deposition methodologies (pulsed laser deposition (PLD)), as an additional opportunity for high-throughput growth of YBCO. As a prerequisite, highly flat and amorphous YBCO precursor films were deposited by PLD at temperatures below 400 ºC on single-crystalline SrTiO3 (STO) and LaMnO3 (LMO)/STO, as well as industrial coated conductor (CC) architectures. Contrary to TLAG based on chemical solution deposition (TLAG-CSD), where BaCO3 elimination is a key factor for the YBCO growth, TLAG-PLD growth is controlled by the transformation of Ba-Cu-O (s) to a transient liquid. High-quality c-axis YBCO films were successfully grown on different substrates, as demonstrated by high-resolution X-ray diffraction and transmission electron microscopy. In-situ resistance measurements revealed that the growth rates around 1000 nm s-1 can be achieved, outperforming the capabilities of standard PLD growth of REBCO films by few orders of magnitude. Experimental conditions such as temperature, oxygen partial pressure, and heating ramp, were optimized to obtain critical temperature (Tc) values up to 90 K. Critical current densities of 15 MA cm-2 at 5 K and 1.7 MA cm-2 at 77 K were obtained for YBCO films of 450 nm on LMO/STO.