Effect of Winding Tension, Support Material, and Epoxy Impregnation on the Strain and Critical Current of YBCO Coil

Liu, Liyuan; Chen, Wei; Zhang, Haiyang; Yang, Xinsheng; Yang, Ye; Zhang, Yong; Zhao, Yong

doi:10.1109/tasc.2017.2655012

Cited by 10 publications

(4 citation statements)

References 20 publications

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“…Separation of the YBCO layer from the substrate under radial stress is often cited as the primary cause of failure of epoxy-impregnated 2G coils [26][27][28]. Currently several approaches to degradation-free impregnation of 2G pancake coils, such as coil sectioning [29], coating or sleeving conductors, or compensation of the transverse stress by tension [30] have been developed and successfully tested. It is highly desirable, however, to retain good thermal contact between the epoxy and the winding.…”

Section: Thermal Stress and Mechanical Stability Of Epoxyimpregnated ...mentioning

confidence: 99%

Performance of layer wound epoxy-impregnated coils made from a multifilamentary cable of exfoliated YBCO

Solovyov

Rabbani

et al. 2019

Supercond. Sci. Technol.

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The performance and reliability of magnets made from second generation (2G), exfoliated, YBCO conductors are highly improved by use of narrow, stacked, multifilamentary cable instead of a single wide tape. This paper reports on tests of five mini-coils wound from 2.4 mm wide ExoCable™, which is comprised of eight, stacked, exfoliated, YBCO filaments. The filaments are coupled electrically through a re-flow process, which results in enhanced electrical connectivity between the adjacent layers. The coils were tested at 77 K (up to 500 A) in liquid nitrogen and at 22 K (up to 700 A) in a conduction-cooled mode. The cable carries 500 A critical current at 77 K. A six-layer coil wound from 10.5 m of the cable, the largest coil created in the study, demonstrates a critical current of 280 A at 77 K at 0.4 T magnetic field on the winding. The coils were fully impregnated with Stycast 1266 and Henkel W19 low-viscosity epoxies. Repeated thermal cycling, to 77 and 22 K, does not degrade the coil’s performance. The cable AC loss and the coil winding magnetization are compared with the traditional 2G wide tape pancake geometry at 77 K. We observe a five times reduction of the winding magnetization when the 12 mm tape is replaced by a 2.4 mm cable, which is explained by the smaller magnetic moment of the cable winding. The field hysteresis profiles recorded at 22 and 77 K are presented to demonstrate the effect of the operation temperature on the winding magnetization. A finite element analysis of the winding magnetization shows a good agreement between the experimentally measured trapped field value, and the critical state model prediction. Finally, we discuss the stability of an ExoCable™ coil in a conduction-cooled operation.

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Section: Thermal Stress and Mechanical Stability Of Epoxyimpregnated ...mentioning

confidence: 99%

Performance of layer wound epoxy-impregnated coils made from a multifilamentary cable of exfoliated YBCO

Solovyov

Rabbani

et al. 2019

Supercond. Sci. Technol.

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“…Therefore, it is essential to study the contact behavior during the winding process. However, the winding is a rather complex deformation process [16][17][18][19]. The actual contact is indeed strongly nonlinear, which leads to difficulties in solving this problem.…”

Section: Introductionmentioning

confidence: 99%

Nonlinear contact behavior of HTS tapes during pancake coiling and CORC cabling

Wang

Gao

Luo

et al. 2021

Supercond. Sci. Technol.

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Both the pancake coiling and conductor on round core (CORC) cabling processes consist of winding second-generation high-temperature superconducting tape (REBCO) in a core. The contact behavior between the tape and the core during the winding process directly affects the critical current, cable flexibility, mechanical support and electrical contact resistance. Therefore, the winding process needs to be optimized to produce pancake coils and CORC cables with the desired electrical and mechanical properties. This paper comprehensively considers the role of the relaxation and Poisson effects. The theoretical model and the finite element model (FEM) for calculating the contact stress during the winding process are established, and a formula for the estimation of the contact force is proposed. The suitable winding pre-tension force, winding curvature radius of SCS2030 (2 mm width and 30 μ m substrate thickness) and SCS4050 (4 mm width and 50 μ m substrate thickness) of REBCO tapes are obtained and discussed by accounting for the relaxation effect and the critical current degradation limit. With consideration of the Poisson effect, the nonlinear contact behavior is investigated. In addition, the relaxation effect, Poisson effect and plasticity of the REBCO tape are taken into account in the FEM model. The results show that the axial strain in the REBCO layer during the winding process is related to the contact behavior. The greater the winding pre-tension force, the smaller the helical curvature radius, and the greater the contact force. The distribution of contact stress for several winding factors (winding pre-tension force, winding angle and the core radius) is divided into three contact types: the single-line contact, the double-line contact and the surface contact. The FEM model results are consistent with the theoretical evaluation and are more suitable for practical winding cases. This research is the basis for designing and optimizing pancake coils and CORC cables.

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“…under shear-and cleavage stress can be as low as some 0.5 MPa [122]. Different thermal expansion coefficients of the materials in both the winding pack and tapes themselves may cause these stresses to appear in an impregnated coil [119]. Numerous methods were proposed to reduce this thermal-stress related degradation.…”

Section: Rebco Coilsmentioning

confidence: 99%

“…Currently, ReBCO coils are being developed further following all three winding strategies: insulated, not insulated and partially insulated. The best choice strongly depends on the targeted application.Regardless of the chosen winding method, ReBCO coils are often impregnated to prevent conductor motion and to increase the coil's mechanical strength[118,119]. Both vacuum impregnation and 'wet' winding can be employed.…”

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confidence: 99%

Conduction-cooled ReBCO coils for the wind converter: from laboratory to field test

Bergen

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Practical high-current applications of low-temperature superconductors (LTS) include magnetic resonance imaging, nuclear magnetic resonance and large magnet systems for high-energy physics and nuclear fusion. Higher magnetic fields and higher operating temperatures require a changeover to high-temperature superconductors (HTS) such as ReBCO. These ceramic materials have a critical temperature T c above the normal boiling point of nitrogen, which in principle allows them to be cooled by liquid nitrogen instead of liquid helium. Using liquid nitrogen instead of liquid helium can simplify the design of the cooling system for the superconducting application. A disadvantage of such a 'wet' magnet is the limited operating temperature range and the requirement of periodic refills which is problematic in the case of non-continuous supply of the cryogenic liquid. Use of cryocoolers, on the other hand, allows the superconducting magnet to be conduction-cooled also to intermediate temperatures. Gifford-McMahon type crycoolers are most commonly used today due to their relatively low cost and high reliability. The

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Effect of Winding Tension, Support Material, and Epoxy Impregnation on the Strain and Critical Current of YBCO Coil

Cited by 10 publications

References 20 publications

Performance of layer wound epoxy-impregnated coils made from a multifilamentary cable of exfoliated YBCO

Performance of layer wound epoxy-impregnated coils made from a multifilamentary cable of exfoliated YBCO

Nonlinear contact behavior of HTS tapes during pancake coiling and CORC cabling

Conduction-cooled ReBCO coils for the wind converter: from laboratory to field test

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