Investigation about the effects of metal-clad winding on the electromagnetic characteristics of the GdBCO racetrack coils in a time-varying magnetic field

Kim, J.M.; Kim, Y.G.; Hong, Sung‐Eun; Park, S.J.; Kim, J.H.; Kim, H.M.; Choi, Yeon Suk; Lee, H.G.

doi:10.1016/j.rinp.2018.09.034

Cited by 9 publications

(4 citation statements)

References 26 publications

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“…Several studies have focused on the performance of NI-HTS coils operating under overcurrent conditions. Experimentally, a saturation of the magnetic field was observed in various overcurrent tests [7,[9][10][11], and burnout [11] of both the innermost and outermost turns close to the electrodes occurred [12]. Similar phenomena were also observed during overcurrent tests of HTS coils with turn-to-turn metal insulation [13,14].…”

Section: Introductionmentioning

confidence: 57%

Magnetic Field Saturation of Non-Insulation High-Temperature Superconducting Coils during Overcurrent

Gao

Jin

2021

Electronics

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Non-insulation high-temperature superconducting coils provide a much lower risk of burnout in fault/abnormal conditions, such as hot-spot quench and overcurrent. This study employs an equivalent circuit grid model, coupled with magnetic field calculation and the E–J power law of superconductors, to deeply and systematically investigate the overcurrent charging process in a double-pancake non-insulation coil. An evident saturation of the magnetic field in the axial direction of the coil was observed and verified by experiments. Experimentally, the entire process, including the behavior of the magnetic field, was consistent with the numerical results. Based on the verified model, two main points were addressed: (1) Transient current distribution inside the coil during overcurrent charging was studied. Potential quenching risks were found to be at the innermost and outermost turn near the electrodes, as well as the pancake-to-pancake connection part. (2) Magnetic field saturation, which is a unique phenomenon in non-insulation superconducting coils during overcurrent charging, was studied in detail and first quantitatively defined by a new concept “converged load factor”. Its relationship with turn-to-turn resistivity was revealed.

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Section: Introductionmentioning

confidence: 57%

Magnetic Field Saturation of Non-Insulation High-Temperature Superconducting Coils during Overcurrent

Gao

Jin

2021

Electronics

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“…Heydari et al have applied two auxiliary windings to reduce the leakage flux in HTS transformers so that the AC loss of HTS coils can be decreased by about 13.6% [242]. Kim et al have employed a metal-clad (MC) winding technique for non-insulated (NI) HTS coils to enhance the turn-to-turn resistance by adding a 5-µm-thick coating of stainless steel to a copper-stabilized HTS CC [243]. It has been demonstrated that the NI coil has the least AC loss, followed by the NI coil with the MC winding technique, and the insulated coil has the highest AC loss.…”

Section: Winding Techniquesmentioning

confidence: 99%

“…It has been demonstrated that the NI coil has the least AC loss, followed by the NI coil with the MC winding technique, and the insulated coil has the highest AC loss. However, it should be noted that the AC transport current loss tests in [243] were performed at 20 Hz, i.e., at low frequencies. Therefore, the effectiveness of the added metal clad in a high-frequency electromagnetic environment (e.g., in high-speed rotating machines) remains unclear.…”

Section: Winding Techniquesmentioning

confidence: 99%

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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“…Researchers have studied the inductive voltages of NI coils caused by their electromagnetic induction with external AC magnets [20][21][22], resistive voltages of NI coils with the observation of a local thermal quench under time-varying fields [5,23,24] and the critical current degradation of NI coils caused by an axial AC field [5,25]. However, the unique behaviors of NI magnets affected by the dynamic resistance have not yet been clearly observed.…”

Section: Introductionmentioning

confidence: 99%

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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Investigation about the effects of metal-clad winding on the electromagnetic characteristics of the GdBCO racetrack coils in a time-varying magnetic field

Cited by 9 publications

References 26 publications

Magnetic Field Saturation of Non-Insulation High-Temperature Superconducting Coils during Overcurrent

Magnetic Field Saturation of Non-Insulation High-Temperature Superconducting Coils during Overcurrent

Alternating Current Loss of Superconductors Applied to Superconducting Electrical Machines

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

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