Melt textured YBa₂Cu₃O_ybulks with artificially patterned holes: a new way of processingc-axis fault current limiter meanders

Abstract

YBa2Cu3Oy (Y123) bulk materials were textured with artificially patterned holes, creating a ‘perforated structure’. The goal is to facilitate sample oxygenation and decrease crack formation in order to address the problem of hot spot formation in fault current limiter (FCL) applications. As-processed samples contained mechanically patterned holes parallel to the mean c-axis interconnected to the textured domain. This makes samples easier to oxygenate and cool. The microstructure is not distorted in the vicinity of the holes. The single domain character of the sample is evidenced by XRD pole figure investigations. Meander tracks were prepared by drilling the upper and lower surfaces of the samples. Samples containing holes still trap high fields, comparable with samples without holes. Values of Jc are increased in samples with holes.

EBSD study on YBCO textured bulk samples: correlation between crystal growth and ‘microtexture’

“…Those measurements have shown that the texture development in the total volume, as seen macroscopically, is not influenced by the presence of holes in the pellet [26]. At the same time, SEM microscopic observations indicate that the local microstructure is preserved even in the vicinity of holes.…”

“…The powder mixture was pelletized uniaxially and then sintered at 920 • C for 24 h. Regularly spaced 1 mm diameter holes were drilled into sintered bulk samples before the standard melt process is operated. After the growth step, the samples were submitted to an additional annealing under oxygen flow at 450 • C for 150 h in order to obtain good superconducting properties [26,28].…”

Improvement of Critical Current Density and Flux Trapping in Bulk High-Tc Superconductors

“…For meandering FCL elements, cutting is a crucial step as cracks appear during this stage. This can be solved by the in situ zigzag shape processing of holes, as we demonstrated the feasibility of elsewhere [43]. magnetization using a homemade large dc current source.…”

“…Another unique aspect concerning flux trapping is to distribute holes drilled within the bulk pack. The recently reported [41][42][43][44][45] hole-patterned YBa2Cu3Oy (Y123) bulks with improved superconducting properties are highly interesting from the points of view of material quality and their variety of application. It is well known that the core of plain bulk superconductors needs to be fully oxygenated, and some defects like cracks, pores and voids [46,47] must be suppressed in order that the material can trap a high magnetic field or else carry a high current density.…”

“…As an example, the artificial drilled Y123 in a desired structure [43,57] is a good candidate for resistive elements in superconducting fault current limiters (FCL) [58,59]. In this application, the thin wall between the holes allows more efficient heat transfer between a perforated superconductor and cryogenic coolant during an over-current fault compared with conventional bulk materials.…”