500 V/200 A fault current limiter modules made of large-area MOD-YBa₂Cu₃O₇thin films with high-resistivity Au–Ag alloy shunt layers

Abstract

We developed 500 Vrms/ 200 Arms superconducting thin-film fault current limiter (FCL) modules that can withstand high electric fields (E>30 Vrms cm−1) by using large-area YBa2Cu3O7 (YBCO) thin films with high-resistivity Au–Ag alloy shunt layers. Au–Ag alloy films about 60 nm thick were sputter-deposited on YBCO/CeO2/sapphire films (2.7 cm × 20 cm) prepared using a fluorine-free MOD method. Each 20 cm long Au–Ag/YBCO film was then divided into three segments (each ∼5.7 cm long) by four Ag electrodes deposited on the Au–Ag layer, resulting in an effective length of 17 cm. The 500 V/200 A FCL modules were then fabricated by first connecting two of the segmented films in parallel using Ag-sheathed Bi-2223 superconducting tapes and then connecting in parallel an external resistor and a capacitor for each segment to protect the Au–Ag/YBCO film from hot spots. Switching tests using a short-circuit generator revealed that all the modules carried a superconducting ac current of ≥237 Arms and that modules prepared with YBCO films having a relatively homogeneous critical current Ic distribution successfully withstood ≥515 Vrms for five cycles without any damage. These results demonstrate that (a) the FCL modules fabricated here successfully achieved the rated current of 200 Arms and rated voltage of 500 Vrms and (b) total area of the YBCO films on sapphire substrates required for the 500 V/200 A (100 kV A) module was less than one-third that for conventional thin-film FCL modules that use gold shunt layers, leading to the significantly reduced cost of thin-film FCLs. Film damage due to hot spots depended on the difference in Ic between the two parallel-connected films and on the inhomogeneity of the Ic distribution in the film, and is most probably due to nonlinear current flows at the moment of quenching that cause local overheating.

Effect of inductors to mitigate the hot-spot problem in parallel-connected superconducting thin-film fault current limiting elements

“…Then, the dissipated power density should depend strongly on the critical sheet current I c /W. This is reasonably understood and is consistent with our observation that the hot-spot problem is more severe in the commercial THEVA films with higher I c /W values than in the MOD films with lower I c /W [16,23]. However, the phenomenon that the hot-spot problem is more severe in films with a higher total I c cannot be easily understood, because the average power density calculated by (1) should be unchanged when composite AuAg/YBCO films with the same specifications are used.…”

“…We have succeeded in fabricating and testing FCL modules with a rated voltage/current of 500 V rms /200 A rms , using 20 cm long MOD-YBCO films [23]. The 100 kVA FCL module requires a total sapphire substrate area of 126 cm 2 , which is less than one-sixth that for the Siemens 100 kVA functional model [5], and less than one-third that for the Korean demonstrator [6].…”

Strong flux pinning due to dislocations associated with stacking faults in Y Ba2Cu3O7 − δthin films prepared by fluorine-free metal organic deposition

“…FF-MOD films #1 and #2 with thickness of 150 nm were cut from a large-area YBCO/CeO 2 /sapphire film (2.7 cm × 20 cm) that was used to prepare fault-current limiting modules [4]. Figures 1(a) and (b) show the J c (H, θ) data for films #1 and #2, respectively.…”

“…YBa 2 Cu 3 O 7−δ (YBCO) epitaxial films in the form of coated conductors or large-area thin films are applied to various power devices, such as power transmission cables, high-field magnets and fault-current limiters [1][2][3][4], and high critical current density J c is required to reduce the volume and cost of superconductors. If the flux pinning mechanisms in YBCO films are clarified, then pinning centers can be effectively introduced to substantially improve J c and to maintain high J c in thick films ( 1 μm) by overcoming the decrease of J c with film thickness that has often been observed in YBCO films.…”

Preparation of superconducting films by metal organic deposition

“…[35] (2) AIST research: The 500 V/200 A single-phase FCL unit that used the noninductive shunt resistance developed by AIST was used to limit the peak current of 3.5 kA to 770 A. [36] The cost of the large-area superconducting film used for FCL in the dispersed distributed power supply site was calculated, and it was shown that in the future it will be lower than the target cost of realization. [37] Based on these results, the technological transfer to companies of the large-area superconducting film manufacturing process is being promoted.…”