Study of the inhomogeneity of critical current under<i>in</i>-<i>situ</i>tensile stress for YBCO tape

Zhu, Yunpeng; Chen, W; Zhang, H Y; Liu, L Y; Pan, Xifeng; Yang, Xinsheng; Zhao, Yong

doi:10.1088/1361-6668/aaa81f

Cited by 7 publications

(7 citation statements)

References 28 publications

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“…As a consequence, the local power dissipation P ws = E ws I∆x ws will start. We focus here on investigating a small-scale nonuniformity with ∆x ws in the millimeter range [37,42,73]. Then, the weak spot temperature, T ws , can be considered uniform in the whole volume of the conductor within ∆x ws .…”

Section: Formulation Of the Problemmentioning

confidence: 99%

“…Our analysis is similar to the stability study of HTS coils [69][70][71]; however, the heated region is not the whole coil winding but only the weak spot and its surroundings. Longitudinal heat flow along the conductor length is considered relevant in the cooling of defects with the length of a few millimeters [72,73]. On the other hand, we disregard a lateral non-uniformity, and assume that the local heating happens in a strip stretched across the tape width [74][75][76].…”

Section: Introductionmentioning

confidence: 99%

“…For currents up to a certain limit, marked I tr , the temperature would rise for some time, and then attain a stable value. When the supplied current is above I tr , a fast rise of temperature occurs called the 'thermal runaway' [16,30,[77][78][79], and the weak spot converts to the 'hot spot' [44,49,73,80,81]. A reliable prediction of the thermal runaway current, I tr , is therefore of utmost importance.…”

Section: Introductionmentioning

confidence: 99%

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Stability of DC transport in HTS conductor with local critical current reduction

Gömöry

Šouc

2021

Supercond. Sci. Technol.

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A common feature of commercially available conductors based on high-temperature superconducting compounds is the fluctuation of critical current along the length. Fortunately, the practice adopted by manufacturers nowadays is to supply the detailed I c(x) data with the conductor. Compared to knowing just the average of critical current, this should also allow a much better prediction of the conductor performance. Statistical methods are suitable for this purpose in the case when the fluctuations are regular at the low end of critical current distribution. However, a different approach is necessary at the presence of ‘weak spots’ that drop out of any statistics. Because of the strong nonlinearity of the current–voltage curve, such a location could transform into a ‘hot spot’ at transporting direct current (DC), with an abrupt increase of temperature endangering the conductor operation. We present a set of analytical formulas including the prediction of the maximum DC that could be carried sustainably before the thermal runaway appears. It is necessary to know the cooling conditions as well as the properties of the conductor constituents and their architecture. A formula for the voltage appearing on a weak spot, and its dependence on the DC, is also proposed. For this purpose the result of previous theoretical work has been slightly modified after comparing it with numerical iterative computations and finite element modeling. We demonstrate that the derived model allows a powerful analysis of experimental data comprising an estimation of the weak spot parameters i.e. its critical current and the length of the defect zone.

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Section: Formulation Of the Problemmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Stability of DC transport in HTS conductor with local critical current reduction

Gömöry

Šouc

2021

Supercond. Sci. Technol.

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“…NTRINSICALLY, local defects reduce local critical currents and are not avoidable in a coated conductor even by using the most advanced manufacturing technology [1][2][3][4][5][6].…”

Section: Introductionmentioning

confidence: 99%

Thermal Runaway of Conduction-Cooled Monofilament and Multifilament Coated Conductors

Luo

Zhao

Sogabe

et al. 2022

IEEE Trans. Appl. Supercond.

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We experimentally studied the thermal runaway initiating at a low critical current (Ic) part. This low Ic part is determined by the combination of two reasons in a real coil: (a) the unavoidable defects caused by the manufacturing process, which reduce local critical currents (and might not be uniform across the width of a coated conductor) and (b) the magnetic field distribution along the coated conductor. To simulate the thermal runaway using a short monofilament/multifilament REBa2Cu3Oy (RE-123) coated conductor, we artificially created a local defect (low Ic part) in a short sample by pressing using a drill bit (creating a defect close to one edge of a coated conductor) or bending (creating a uniform defect across the width of a coated conductor). The sample of the coated conductor was conduction-cooled to 30 K, and a magnetic field was applied (µ0H up to 2 T) perpendicular to the wide face of the conductor to control its critical current. Transverse voltages in a multifilament coated conductor were measured to obtain the transverse currents among the filaments through the copper layer. Thermal runaway currents (operating currents above which thermal runaway initiates) of the monofilament sample and those of the multifilament sample with additional Joule loss due to the transverse currents were determined and compared to study the effect of the transverse currents on the initiation of thermal runaway in the multifilament coated conductor. Experiments on the protection against thermal runaway were conducted. When a normal voltage (over a preset threshold) was detected, the supplied current would be decreased exponentially. The thresholds for protecting monofilament and multifilament coated conductors from degradation after thermal runaway were compared.

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“…The strain can easily lead to the production of local microcracks, causing inhomogeneity of the critical current. With this increase of inhomogeneity, heat spots may appear more frequently and the AC loss may increase [11,12]. Therefore, it is necessary to evaluate and simulate the critical current distribution in practical applications.…”

Section: Introductionmentioning

confidence: 99%

Non-destructive evaluation of critical current on a Bi-2212 first stage cable based on numerical analysis of the remnant field distributions

Chen¹,

Yang²,

Hao³

et al. 2018

Supercond. Sci. Technol.

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The high temperature superconducting material Bi-2212 is considered for use in the next generation of fusion reactors due to an excellent current carrying capacity in a high field. The critical current as well as its inhomogeneity are important factors in evaluating the performance of Bi-2212 wires, cables and conductors. Non-destructive evaluation by using a Hall sensor array is a more effective and faster method for testing the local critical current of a high temperature superconductor compared with a conventional contact-electrical method. In this paper, the coupling and decoupling numerical models of the perpendicular component of the residual magnetic field in Bi-2212 round wire were solved. Then, the perpendicular component of the remnant magnetic field was measured by a Hall sensor array, which was consistent with the results of the coupling model. Our results established the numerical model for a Bi-2212 first stage cable and found that the non-destructive method using four mutual vertical Hall sensor arrays is feasible for evaluation of cable critical current properties.

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Study of the inhomogeneity of critical current underin-situtensile stress for YBCO tape

Cited by 7 publications

References 28 publications

Stability of DC transport in HTS conductor with local critical current reduction

Stability of DC transport in HTS conductor with local critical current reduction

Thermal Runaway of Conduction-Cooled Monofilament and Multifilament Coated Conductors

Non-destructive evaluation of critical current on a Bi-2212 first stage cable based on numerical analysis of the remnant field distributions

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