Advanced design and experiment of a small-sized flywheel energy storage system using a high-temperature superconductor bearing

Abstract. Drilling holes in a bulk high-Tc superconductor enhances the oxygen annealing and the heat exchange with the cooling liquid. However, drilling holes also reduces the amount of magnetic flux that can be trapped in the sample. In this paper, we use the Bean model to study the magnetization and the current line distribution in drilled samples, as a function of the hole positions. A single hole perturbs the critical current flow over an extended region that is bounded by a discontinuity line, where the direction of the current density changes abruptly. We demonstrate that the trapped magnetic flux is maximized if the center of each hole is positioned on one of the discontinuity lines produced by the neighbouring holes. For a cylindrical sample, we construct a polar triangular hole pattern that exploits this principle; in such a lattice, the trapped field is ∼ 20% higher than in a squared lattice, for which the holes do not lie on discontinuity lines. This result indicates that one can simultaneously enhance the oxygen annealing, the heat transfer, and maximize the trapped field.

Section: Introductionmentioning

confidence: 99%

Bulk high-T_csuperconductors with drilled holes: how to arrange the holes to maximize the trapped magnetic flux?

Lousberg

Ausloos

Vanderbemden

et al. 2008

“…In recent years, with the continuous improvement of the fabrication processes of melt-textured bulk high-temperature superconductors, large bulk RE-Ba-Cu-O (RE denotes rare Earth elements) has shown great potential in large-scale engineering applications such as permanent magnets [1]; superconducting magnetic bearings and flywheel energy storage systems [2][3][4][5]; and superconducting noncontact conveyors or torque transfers [6,7], due to its unique properties of auto-stable levitation and a stronger ability to trap magnetic fields than iron-based, permanent magnets. In particular, bulk Y-Ba-Cu-O (YBCO) has become an appealing candidate for industrial application material because the preparation method is simple, reliable and low cost.…”

Section: Introductionmentioning

confidence: 99%

Influence of layered precursor pellets on the growth and properties of Y-Ba-Cu-O bulk superconductors by top-seeded melt-textured growth

Tang

2016

It is well known that a fine and homogeneous distribution of Y2BaCuO5 (Y211) phase particles in single-grain Y-Ba-Cu-O (YBCO) bulk superconductors is essential for improving field-trapping ability. However, the size and concentration of Y211 phase particles in the fully melt-processed superconducting bulk increase significantly with the distance from the seed, which results in the accumulation of Y211 phase particles and the degradation of superconducting properties. In this paper, we report a new method of fabricating single-grain YBCO using layered precursor pellets. Using the top-seeded melt-textured growth process, single-grain YBCO bulk superconductors of about 22 mm in diameter and 9 mm in thickness were fabricated from layered precursor pellets and standard precursor pellets, respectively. The layered precursor pellets consist of precursor powders with 40 mol% Y211 at the top, 30 mol% Y211 in the middle and 20 mol% Y211 at the bottom of the whole pellets, while standard precursor pellets are prepared from precursor powders with only 40 mol% Y211. The growth morphology, microstructure and magnetic flux properties of the layered samples and standard samples were comparatively studied. The results proved that the layered precursor pellets allow a sufficient growth in the c-growth sector and a more uniform distribution of the Y211 phase in the matrix. The distribution of Y211 phase particles is qualitatively explained by the prevalent trapping/pushing theory. The trapped field at 77 K reaches 0.8 T, nearly 29% higher than the standard sample. The present results are very valuable for further improving the properties of YBCO bulk superconductors.

“…Y-Ba-Cu-O (YBCO) single grains have shown the unique properties of auto-stable levitation and large magnetic field trapping ability, which are highly attractive for a variety of engineering applications such as permanent magnets, superconducting motors, and flywheel energy storage devices [1][2][3]. It is well known that the levitation force and the field trapping capability of a bulk superconductor are proportional to the size of the single domain, therefore, enlargement of the cross-sectional area of the bulk is one of the most important issues.…”

Section: Introductionmentioning

confidence: 99%

“…However, it is still difficult at present to grow large single domains with diameters larger than 50 mm by commonly used melt-textured growth processing. This is because of the following reasons: (1) a long processing time due to the slow growth rate of YBa 2 Cu 3 O 6.5 (Y-123) grains, which will bring about serious problems such as selfinduced crystallization and Ostwald ripening of Y 2 BaCuO 5 3 Author to whom any correspondence should be addressed.…”

Section: Introductionmentioning

confidence: 99%

A new seeding approach to the melt texture growth of a large YBCO single domain with diameter above 53 mm

Fang

et al. 2009

A new approach for growing large size single domains of Y–Ba–Cu–O by a top-seeded melt-textured growth (TSMTG) process is reported. Contrary to the commonly used TSMTG method using a small seed crystal that has been difficult to use to grow well-textured single domains with diameters above 50 mm, we adopt a large well-textured SmBCO bulk with a size of 14 × 14 mm2 as a seed to grow YBCO single domains. Experimental results show that this new approach can not only quicken the growth rate of the bulk, but also result in a better textured structure. By using this method, large YBCO single domains of up to 53 mm in diameter have been successfully produced and 75 mm diameter samples can also be grown. Microstructure analysis of these as-grown YBCO bulks shows a good c-axis orientation in crystallization, and magnetic levitation force measurements show that the bulks 53 mm in diameter have excellent magnetic levitation performance, with levitation force of up to 334 N (77 K, 0.5 T), corresponding to a force density of 15.2 N cm−2.