Dependence of Dynamic Loss on Critical Current and n-Value of HTS Coated Conductors

Zhang, Hongye; Yao, Min; Jiang, Zhenan; Xin, Ying; Li, Quan

doi:10.1109/tasc.2019.2948993

Cited by 49 publications

(34 citation statements)

References 19 publications

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“…However, analytical loss calculations are imperfect in that the formulae have been derived based on some fundamental assumptions, e.g., constant critical current, homogenous external field, thin film approximation for HTS CCs, etc. [55][56][57][58][59][60][61][62][63][64]. Besides, the analytical equations are normally limited to simple structures, e.g., single tapes or wires; thus, in superconducting machines, the analytical equations are not enough to accurately quantify the practical AC loss.…”

Section: Modelling Methodsmentioning

confidence: 99%

“…The dynamic loss is calculated by measuring the voltage along with the transport current of the coated conductor sample. The measurement method has been extensively applied to much experimental exploration of dynamic loss and dynamic resistance of HTS CCs [16,63,64,[158][159][160][161]. Ogawa has studied the magnetization loss and dynamic loss of an HTS pancake coil with a double pick-up coil method and found that the dynamic resistance can mitigate the DC of the coil when it is operated in the permanent current mode [135].…”

Section: Electric Methodsmentioning

confidence: 99%

“…For field coils embedded on the rotor in a superconducting machine, each HTS CC carries DC and is exposed to time-varying magnetic fields. In this case, dynamic loss (W/m) occurs in the HTS layer and can be calculated by [63]…”

Section: Analytical Formulae For Ac Loss Calculationmentioning

confidence: 99%

See 2 more Smart Citations

Alternating Current Loss of Superconductors Applied to Superconducting Electrical Machines

Zhang¹,

Wen²,

Grilli

et al. 2021

Energies

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Superconductor technology has recently attracted increasing attention in power-generation- and electrical-propulsion-related domains, as it provides a solution to the limited power density seen by the core component, electrical machines. Superconducting machines, characterized by both high power density and high efficiency, can effectively reduce the size and mass compared to conventional machine designs. This opens the way to large-scale purely electrical applications, e.g., all-electrical aircrafts. The alternating current (AC) loss of superconductors caused by time-varying transport currents or magnetic fields (or both) has impaired the efficiency and reliability of superconducting machines, bringing severe challenges to the cryogenic systems, too. Although much research has been conducted in terms of the qualitative and quantitative analysis of AC loss and its reduction methods, AC loss remains a crucial problem for the design of highly efficient superconducting machines, especially for those operating at high speeds for future aviation. Given that a critical review on the research advancement regarding the AC loss of superconductors has not been reported during the last dozen years, especially combined with electrical machines, this paper aims to clarify its research status and provide a useful reference for researchers working on superconducting machines. The adopted superconducting materials, analytical formulae, modelling methods, measurement approaches, as well as reduction techniques for AC loss of low-temperature superconductors (LTSs) and high-temperature superconductors (HTSs) in both low- and high-frequency fields have been systematically analyzed and summarized. Based on the authors’ previous research on the AC loss characteristics of HTS coated conductors (CCs), stacks, and coils at high frequencies, the challenges for the existing AC loss quantification methods have been elucidated, and multiple suggestions with respect to the AC loss reduction in superconducting machines have been put forward. This article systematically reviews the qualitative and quantitative analysis methods of AC loss as well as its reduction techniques in superconductors applied to electrical machines for the first time. It is believed to help deepen the understanding of AC loss and deliver a helpful guideline for the future development of superconducting machines and applied superconductivity.

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Section: Modelling Methodsmentioning

confidence: 99%

Section: Electric Methodsmentioning

confidence: 99%

See 1 more Smart Citation

Alternating Current Loss of Superconductors Applied to Superconducting Electrical Machines

Zhang¹,

Wen²,

Grilli

et al. 2021

Energies

Self Cite

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show abstract

“…To date, there are several reports on numerical simulations and experimental measurements on total loss of REBCO CCs [43,[51][52][53][54][55][56] , REBCO stacks [54] and REBCO coils [54][55][56] at 77 K. Only one experimental study was conducted on total loss of YBCO-123 CCs under perpendicular magnetic fields [51,52] , where the critical current of the coated conductor was around 40 A. This early-stage coated conductor cannot represent the performance of currently available commercial REBCO CCs.…”

Section: Introduction 11 Motivationmentioning

confidence: 99%

“…This early-stage coated conductor cannot represent the performance of currently available commercial REBCO CCs. The total loss of commercial REBCO CCs were calculated via finite element (FM) simulations, which analyzed the influence of DC currents and AC magnetic fields, instead of the loss evolving process [43,53,54] . The frequency dependence of total loss in REBCO CCs, stack and coils was also studied via FE simulations [54] , which lacked systematic studies on the influence of DC currents and magnetic fields to total loss.…”

Section: Introduction 11 Motivationmentioning

confidence: 99%

AC Loss Research of REBCO High-Tc Superconductors Carrying a DC Current in an AC Magnetic Field

Sun¹

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AbstractREBCO (REBa2Cu3O7-d, RE stands for rare earth) high temperature superconducting (HTS) coated conductors (CCs) have become the preferred wire choice for HTS applications due to their high current carrying capacity and advanced mechanical properties. In many HTS applications such as HTS synchronous motors, HTS flux pumps and HTS persistent current switches, REBCO CCs, stacks and coils carry DC currents in an AC magnetic field environment, generating AC loss comprising of dynamic loss component arising from dynamic resistance and the magnetization loss component due to the shielding currents. AC loss behaviours of commercial-available REBCO CCs in such operating conditions haven’t been fully explored with the most prominent research question of how the AC loss and each loss component evolve and behave in the single REBCO CC, REBCO stacks and REBCO coils at different temperatures with various operating conditions. Other interesting open questions are also put forward to underpin relevant engineering applications: how the shielding effect of REBCO CCs influences the eddy current loss in adjacent copper layers at various field orientation; what kind of inherent correlation exists between the asymmetric field-orientation-dependent critical current characteristics and the magnetization loss behaviors; and how the loss behaviours in REBCO stacks and coils differentiate from the REBCO CC; what’s the difference between the REBCO racetrack coil and the REBCO double pancake coil regarding characteristics of the critical current, magnetization loss, dynamic resistance and AC loss under the condition of the combined DC current with the AC magnetic field. This thesis aims to underpin the REBCO HTS applications and reveal the underlying AC loss mechanism through systematically experimental and numerical research on AC loss and dynamic resistance in REBCO CCs, REBCO stacks and REBCO coils that operate at various electromagnetic conditions and temperatures (65 K ~ 77 K). This research has revealed many new phenomena in the loss evolution process and reached illuminating conclusions. We uncover the shielding effect of REBCO CCs under various field orientations is dominated by the perpendicular magnetic field component, and so does the reduced eddy current loss in the adjacent copper layers of the copper-superconductor stacks. When exploring the role of asymmetric field-orientation-dependent critical current on the magnetization loss of REBCO CCs, we reveal that the asymmetry of critical current about the ab-peak within the 360 full-field-angle range causes differences in magnetization loss values at the field angles which are in mirror symmetry relative to the ab-plane. Furthermore, it is surprising and contradicting to find that magnetization loss at any given field orientation is unequal between the positive and the negative half-field cycle due to the asymmetry of critical current upon the field reversal. The asymmetric field-orientation dependence of both critical current and magnetization loss becomes more obvious with the increasing magnetic field amplitudes and the decreasing temperatures. The complicated AC loss evolution process in REBCO CCs under AC magnetic fields and DC currents is probed by demonstrating the striking behaviours: the dynamic loss region and magnetization loss region vary across the conductor width at high magnetic fields or high DC current levels; the (positive) DC current is superposed with the anti-parallel (negative) shielding current at high DC current levels that approaching to the self-critical current, which drives the local current density of one conductor edge to the subcritical stage and leads to one-sided loss generation in each half-cycle. At the liquid nitrogen temperature range, experimental and simulation results exemplify that the AC loss is mostly dominated by magnetization loss when DC current is less than 20% critical current, while dynamic loss makes a comparable, even greater contribution to AC loss when DC current is larger than 50% critical current. The dynamic resistance shows an obvious frequency dependence due to the heating accumulation at high field amplitudes, high DC current levels and high operating temperatures, which provides a useful reference for the application designs of HTS flux pumps and HTS persistent current switches. Compared with the single REBCO CC, the onset of dynamic resistance/loss in REBCO stacks and REBCO coils is much slower, and the contribution of the dynamic loss component to the AC loss is also much smaller. Dynamic loss in the stack becomes greater than the magnetization loss when the DC current is larger than 70% critical current, while always less than the magnetization loss in the coils when the AC magnetic field is less than 0.1 T. We also conclude that the critical current, magnetization loss and dynamic resistance/loss per unite length in the REBCO racetrack coil is slightly larger than those of the REBCO pancake coil. The main contribution of this work is to reveal the complex AC loss mechanism in REBOC CCs, stacks and coils carrying DC currents in the AC magnetic field and characterize the loss behaviours via solid experimental measurements and numerical simulations. Meanwhile, the magnetization loss as the dominant loss component is further explored concerning its shielding effect and the asymmetric critical current characteristics. This work exemplifies the underlying nature of AC loss behaviours, providing a valuable reference to understand the loss mechanism and to underpin relevant HTS applications.

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Temporal and photon number resolution of superconducting nanowire single-photon detectors

Xie,

Zhang

2024

Appl. Phys. B

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Dependence of Dynamic Loss on Critical Current and n-Value of HTS Coated Conductors

Cited by 49 publications

References 19 publications

Alternating Current Loss of Superconductors Applied to Superconducting Electrical Machines

Alternating Current Loss of Superconductors Applied to Superconducting Electrical Machines

AC Loss Research of REBCO High-Tc Superconductors Carrying a DC Current in an AC Magnetic Field

Temporal and photon number resolution of superconducting nanowire single-photon detectors

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