An equivalent homogenized model for non-superconducting joints made by ReBCO coated conductors

Self Cite

Owing to the presence of joint resistance and flux creep, high-temperature superconducting (HTS) coils without a power supply inevitably suffer from current decay. A flux pump is a voltage supply that requires connections with smaller footprints and a lower heat load than traditional current leads. In this study, we explain the principle of the upper limit for the output current of the traveling wave flux pumps. Based on this principle, a miniaturized linear flux pump device was developed. With narrow and misaligned iron teeth, elaborate 3D geometry of the iron pieces, and optimized driving current waveform, the miniaturized flux pump can support more than 120 A output current with only a 10 mm wide HTS tape and a compact size of 4.6 × 4.6 × 3.4 cm. Our experimental results show that the critical current of the HTS tape has a significant effect on the flux pump output. An HTS tape with a larger critical current supports a higher maximum transport current, whereas an HTS tape with a smaller critical current requires less applied current for positive output. Finally, excitation tests on HTS coils were performed. Charge/active discharge and field supplement experiments were done on a maglev HTS racetrack coil of 0.4 H, where charging/field supplement capbility of the miniaturized flux pump were demonstrated up to 46.8 A (close to the critical current of the coil). It has also been proved that the flux pump can work together with an external power supply with persistent current switch. The miniaturized flux pump can also independently charge an HTS coil of 60 μH to 91.6 A, which is the critical current of the coil at a low voltage criterion.

Section: Hts Coil Excitation Experiments IImentioning

confidence: 99%

Miniaturized HTS linear flux pump with a charging capability of 120 A

Chen

et al. 2023

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“…In this study, the equivalent circuit model in figure 1 considers a number of turns of the NI closed-loop coil as one L-R circuit element, and a total of m elements are connected in series to comprise the coil [17]. Additionally, the joint resistance (R j ) [18] and PCS resistance (R PCS ) are considered in this model, because that they are assembled to fabricate the NI closed-loop coil. According to the Kirchhoff's voltage law, the voltage of the i th circuit element can be derived using equation (1):…”

Section: Equivalent Circuit Modelmentioning

confidence: 99%

Study on current discrepancy and redistribution of HTS non-insulation closed-loop coils during charging/discharging and subsequent transient process toward steady-state operation

Gao

et al. 2022

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It has been previously demonstrated that currents in HTS non-insulation (NI) coils exhibit a discrepant distribution during charging and discharging. However, for NI closed-loop coils, novel phenomenons that arose from the current discrepancy have not been fully studied, especially during transient processes after charging and discharging, or more strictly speaking, after the persistent current switch returns to the superconducting state. For example in our project of a prototype maglev system, a rapid decrease in the magnetic field was observed immediately after charging, which could be easily misinterpreted as a sign of local damage. However, the subsequent stability of the magnetic field with the expected decay rate of < 1\%/day illustrated that there was no such damage. To address this issue, in this study, a NI closed-loop coil was fabricated and simulated by an equivalent circuit model (per 46 turns as a L-R circuit element and 20 elements in total for 920 turns) coupled with a 3D finite-element-method model. Simulated results were in reasonable agreement with experimental measurements, demonstrating a significant discrepancy in azimuthal currents during charging and discharging; this is essentially due to variations in inductances across each turn of NI coils. Besides, azimuthal currents may initially flow in the direction opposite to the coil voltage in turns with lower resistivity relative to other turns. In correspondence with the observed novel phenomenons, after charging or discharging, azimuthal currents undergo redistribution until converging to a stable value, which exhibits a transient process and leads to a rapid decrease or increase of magnetic field in specific positions. The following issues were also discussed: 1) The judgement of operational current could be disturbed by the discrepant current distribution, due to its impact on the spatial magnetic field, not only for NI closed-loop coils but also for open-loop ones; 2) The non-uniformity of currents in NI closed-loop coils is lower, compared to that in open-loop ones with the same joint resistance and turn-to-turn resistivity distribution; 3) A new strategy with multiple charging processes is necessary for precisely charging NI closed-loop coils to the target current.

“…From figure 13(a), it is seen that the HTS windings present high flatness, enabling to better contact with the cooling plates. The critical currents of the two HTS coils were separately measured at 77 K. Figure 14 shows the measured voltagecurrent curves and fitting ones with the following fitting formula (13), that is widely used to characterize the voltagecurrent behaviour of HTS tapes [37], non-superconducting joints [38], and HTS cables [39],…”

Section: Hts Coilsmentioning

confidence: 99%

Design, fabrication and testing of a coated conductor magnet for electrodynamic suspension

Gong

Wang

et al. 2021

Coated conductor magnet, as the onboard magnet of the electrodynamic suspension (EDS) train, is deemed promising due to its relatively high operating temperature, low cooling cost, and good mechanical tolerance, making the liquid-helium-free high-temperature superconducting (HTS) EDS train possible. In order to promote the progress of the HTS EDS train, this work aims at designing, fabricating and testing a coated conductor magnet as the onboard magnet of EDS train. The HTS magnet is designed with the comprehensive considerations of the electromagnetic calculation, thermal-mechanical coupling analysis, as well as the heat load estimation. The magnet is conduction-cooled without any coolant. A radiation shield was used to reduce the heat leakage, enabling the cryogenic system to provide a better low-temperature environment for the magnet. Through a deliberate design, the magnet was fabricated, including two HTS coils and the tailored cryogenic system. Afterwards, the electromagnetic and thermal performances of this magnet were tested and analysed in detail. It was proven that the magnet can be cooled to below 15 K; besides, the magnet has been successfully charged to 240 A. Further increase in the current is possible because of the high safe margin of the critical currents for both the HTS magnet and its current lead, although a slight performance degradation was observed on two double-pancake coils inside the magnet. The present study will provide useful implications for the design and application of onboard HTS magnets in EDS train.