Sharp demagnetization of closed-loop HTS coil in first cycle of external AC fields induced by unexpected dynamic resistance

Zhong, Zhuoyan; Wu, Wei; Jin, Zhijian

doi:10.1088/1361-6668/ac0f53

Cited by 19 publications

(19 citation statements)

References 28 publications

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“…The trend of U coil (t) follows that of the dynamic resistance with lagging/delay. In our previous study, we observed that the dynamic resistance of an (INS) HTS coil during the first cycle of the applied AC field was significantly greater than that during subsequent cycles [41]. This is because the superconducting current distribution (i.e., the current density distribution along the HTS tape width) in the first cycle is qualitatively different from that in the subsequent cycles: in the first cycle, the superconductor is magnetized from its 'virgin' state by the AC field [41].…”

Section: Time Evolutions Of Central Field and Voltage Of The Ni Magnetmentioning

confidence: 93%

“…The operating DC current, I op , of the HTS coil was provided by the Lakeshore Model 625 magnet source. The transverse AC field with 50 Hz, B AC , was applied by pairs of AC magnets, as detailed in our previous work [41]. The HTS coil was located at the precise central position of these AC magnets.…”

Section: Test Setupmentioning

confidence: 99%

“…(iii) After the central field was stabilized, step (ii) was repeated; the AC field was applied and eliminated again. Before each charging, the NI coil was warmed up above the critical temperature by pumping out the liquid nitrogen and then cooled back to 77 K, in order to eliminate the historical screening current density remaining on the HTS tape surface [41].…”

Section: Test Setupmentioning

confidence: 99%

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Time-variant magnetic field, voltage, and loss of no-insulation (NI) HTS magnet induced by dynamic resistance generation from external AC fields

Zhong

et al. 2023

Supercond. Sci. Technol.

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High-temperature superconducting (HTS) coils serving as DC magnets can be operated under non-negligible AC fields, like in synchronous machines of maglev trains and wind turbines. In these conditions, dynamic resistance generates in HTS tapes, causing redistribution/bypassing of the transport current inside the no-insulation (NI) coil and its unique operational features. This issue was studied by experiments on an NI coil with DC current supply put into external AC fields. Due to the current redistribution induced by dynamic resistance, the central magnetic field and voltage of the NI magnet initially undergo various transient processes, and eventually exhibit a stable central magnetic field reduction and a DC voltage. These time evolutions have implications for a time-varying torque and loss of an HTS machine. These time evolutions are strongly affected by the contact resistivity distribution, and whether it is the first time of the NI magnet being exposed to the AC field, showing several qualitatively different waveforms (e.g., some are even non-monotonic with time). The magnitudes of the stable central field reductions, and their observed linear correlation with the DC voltages are found to be decided by the local contact resistivity of the innermost and outermost several turns. It is also noted that the non-insulated turn-to-turn contact help lessening the loss induced by the dynamic resistance. A numerical model is established to analyse/explain those experimental results by observing the microscopic current distribution. Two risks of quench are noticed: (i) azimuthal current of the middle part turns increases as the AC field is applied; (ii) a concentration of radial current is observed near the terminals of the NI coil.

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Section: Time Evolutions Of Central Field and Voltage Of The Ni Magnetmentioning

confidence: 93%

Section: Test Setupmentioning

confidence: 99%

Section: Test Setupmentioning

confidence: 99%

See 1 more Smart Citation

Time-variant magnetic field, voltage, and loss of no-insulation (NI) HTS magnet induced by dynamic resistance generation from external AC fields

Zhong

et al. 2023

Supercond. Sci. Technol.

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“…One of the major challenges concerning the PCM is that the persistent DC current circulating in the HTS coil would decay when exposed to AC fields due to the DC resistance generated in the superconductor, as illustrated by figure 1. For insulated coils [16][17][18][19], bulks [20,21] and stacks [22,23] that carry a persistent DC current, their demagnetization behavior under external AC fields have been extensively studied.…”

Section: Introductionmentioning

confidence: 99%

Study of the demagnetization behavior of no-insulation persistent-current mode HTS coils under external AC fields by 3D FEM simulation

Zhong,

Wu,

et al. 2024

Supercond. Sci. Technol.

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The no-insulation (NI) winding technique is promising to be applied in the persistent-current mode (PCM) operation of high-temperature superconducting (HTS) coils to provide those advantages. To apply the NI PCM coil, its demagnetization behaviour (i.e., decay of persistent DC current) by external AC field, which occurs in maglev trains, electric machines, and other dynamic magnet systems, is essential to be understood. For this purpose, a 3D FEM model, capturing the full electromagnetic properties of NI HTS coils, is established. This work has studied three kinds of AC fields, observing the impact of turn-to-turn contact resistivity on demagnetization rates, which is attributed to current distribution modulations. Under transverse AC field, the lower contact resistivity attracts more transport current to flow in the radial pathway to bypass the ‘dynamic resistance’ generated in the superconductor, leading to slower demagnetization. Under axial AC field, the demagnetization rate exhibits a non-monotonic relation with the contact resistivity: (1) the initial decrease of contact resistivity leads to concentration of induced AC current on the outer turns, which accelerates the demagnetization; (2) the further decrease of contact resistivity makes the current smartly redistribute to avoid to flow through the loss-concentrated outer turns, thus slowing down the demagnetization. Under the rotating DC field, a hybrid of the transverse and axial fields, the impact of contact resistivity on the demagnetization rate exhibits combined characteristics of the transverse and axial components. Besides, quantitative prediction on the demagnetization rate of NI PCM coil under external AC field is instructive for practical designs and operations, which is tried by this 3D FEM model, and a comparison with experimental result is conducted.

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“…Also, many studies were conducted on magnetization loss in the stacked REBCO coated conductors [39,[145][146][147][148][149][150][151] , and insulated or non-insulated REBCO coils [54,56,[152][153][154][155] . N. Bykovsky et.…”

Section: (B) Measurements For Transport Lossmentioning

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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Sharp demagnetization of closed-loop HTS coil in first cycle of external AC fields induced by unexpected dynamic resistance

Cited by 19 publications

References 28 publications

Time-variant magnetic field, voltage, and loss of no-insulation (NI) HTS magnet induced by dynamic resistance generation from external AC fields

Time-variant magnetic field, voltage, and loss of no-insulation (NI) HTS magnet induced by dynamic resistance generation from external AC fields

Study of the demagnetization behavior of no-insulation persistent-current mode HTS coils under external AC fields by 3D FEM simulation

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

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