Impact of Magnet Geometry on Output of a Dynamo-Type HTS Flux Pump

Badcock, Rodney A.; Phang, Sinhoi; Pantoja, A. E.; Jiang, Zhenan; Storey, J. G.; Sung, Hae-Jin; Park, Minwon; Bumby, Chris W.

doi:10.1109/tasc.2016.2636562

Cited by 42 publications

(30 citation statements)

References 16 publications

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“…Here we now extend this FE model to the closed-circuit case, thus enabling current and voltage outputs to be fully calculated for the full range of operating conditions of the device. We show that this simple two-dimensional (2D) model captures all of the essential electrical behavior that has been observed in experiments [3,7,40], including linear dc I -V characteristics, linear frequency dependences of both the internal resistance and the output voltage, and transient voltage waveforms. We also report further validation of the FE model through experimental measurements of the transient local magnetic field in the plane of the HTS stator tape, which confirm the presence of large overcritical circulating currents as the rotor magnet traverses the stator tape.…”

Section: Introductionmentioning

confidence: 78%

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Mechanism of the High- Tc Superconducting Dynamo: Models and Experiment

et al. 2020

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High-T c superconducting (HTS) dynamos are experimentally proven devices that can produce large (more than a kiloamp) dc currents in superconducting circuits, without the thermal leak associated with copper current leads. However, these dc currents are theoretically controversial, as it is not immediately apparent why a device that is topologically identical to an ac alternator should give a dc output at all. Here, we present a finite-element model and a comparison of it with experiment that fully explain this effect. It is shown that the dc output arises naturally from Maxwell's laws when time-varying overcritical eddy currents are induced to circulate in a HTS sheet. We first show that our finite-element model replicates all of the experimental electrical behavior reported so far for these devices, including the dc output characteristics and transient electrical waveforms. Direct experimental evidence for the presence of circulating eddy currents is also obtained through measurements of the transient magnetic field profile across the HTS tape, using a linear Hall array. These results are also found to agree closely with predictions from the finite-element model. Following this experimental validation, calculated sheet current densities and the associated local electric fields are examined for a range of frequencies and net transport currents. We find that the electrical output from a HTS dynamo is governed by the competition between transport and eddy currents induced as the magnet transits across the HTS tape. The eddy currents are significantly higher (approximately 1.5 times) than the local critical current density, and hence experience a highly nonlinear local resistivity. This nonlinearity breaks the symmetry observed in a normal ohmic material, which usually requires the net transport current to vary linearly with the average electric field. The interplay between local current densities and nonlinear resistivities (which both vary in time and space) is shown to systematically give rise to the key observed parameters of experimental HTS dynamo devices: the open-circuit voltage, the internal resistance, and the short-circuit current. Finally, we identify that the spatial boundaries formed by each edge of the HTS stator tape play a vital role in determining the total dc output. This offers the potential to develop alternative designs for HTS dynamo devices, in which the internal resistance is greatly reduced and the short-circuit current is substantially increased.

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Section: Introductionmentioning

confidence: 78%

“…Data are collected using an experimental HTS dynamo similar to that studied in previous work [12,40], depicted in Fig. 1(a).…”

Section: Experimental Methodsmentioning

confidence: 99%

Mechanism of the High- Tc Superconducting Dynamo: Models and Experiment

et al. 2020

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“…The geometry of the HTS dynamo is shown in Fig. 1 with the assumed parameters in Table I, which are based on the 2D HTS dynamo benchmark problem recently proposed in [6] and correspond to the experimental setup in [21].…”

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confidence: 99%

Modelling the Frequency Dependence of the Open-Circuit Voltage of a High-T _c Superconducting Dynamo

Ainslie

Quéval

Mataira

et al. 2021

IEEE Trans. Appl. Supercond.

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A high-Tc superconducting (HTS) dynamo enables the injection of large DC currents into a superconducting circuit, without the requirement for current leads. In this work, we attempt to explain the frequency dependence of such dynamos/flux pumps reported in the literature, where it is observed that the rate at which the open-circuit DC voltage increases reduces with increasing frequency, in contrast to the expected linear behaviour. Heat generated in the HTS wire has been the common explanation given to date for this phenomenon. Here we offer an alternative explanation: the interaction between and current flow in the different layers of the HTS wire as the frequency of the dynamo increases. Our claim is based on numerical analysis using a segregated H-formulation finite-element model of the HTS dynamo benchmark problem that is extended to include the full HTS wire architecture and coupled with a thermal model. This framework enables us to efficiently model the relative movement between the rotating room-temperature permanent magnet and the stationary HTS wire and to study the impact of the frequency of rotation and temperature on the open-circuit DC voltage of the dynamo.

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“…The whole system was submerged in a liquid nitrogen bath and cooled to 77 K. From the experimental results, the magnet geometry and stator width for an optimal FP performance were determined. The results have been published in [3].…”

Section: List Of Figuresmentioning

confidence: 99%

“…The lines joining the data points are guides to the eye. The forward data has been published in[3] and the reverse data is included for comparison.…”

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confidence: 99%

Current-pumping performance of axial-symmetric superconducting dynamo designs

Phang¹

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<p>In this project, the current pumping performances of three high temperature superconducting (HTS) dynamos (mechanically-rotating flux pumps) were investigated. These flux pumps (FPs) were identified as the Gen 1, Gen 2 and Gen 4 FP respectively. They were modelled using simple DC equivalent circuits and their performances were defined by three output parameters: DC open-circuit voltage (Voc), dynamic resistance (Rd) and DC short-circuit current (Isc). The experimental results showed that these FPs produced non-zero DC output voltages across their stators and each supplied DC output currents into series connected superconducting circuits. The Gen 1 FP was cooled with liquid nitrogen and operated at 77 K. The stators were made from 12-mm wide copper-coated yttrium barium copper oxide (YBCO) HTS conductors. The objective of the experiment was to investigate the effect of the rotor magnet size, geometry and orientation (with respect to the stators) on the FP performance. The design parameters, based on the width and the length of the magnet with respect to the stator, for optimal FP performance were determined. The Gen 2 FP was also cooled with liquid nitrogen and operated at 77 K. The stators were made from 46-mm wide Ag-coated YBCO HTS conductors. The objective of the experiment was to investigate the effect of stator width on the FP performance at various magnet frequencies. This was done by slitting two of the stators to form parallel stators with equal width, but smaller than the original conductor width. The experimental results showed that the FP performance was highly dependent on the operating frequency. Three operating frequency regimes were observed: low, mid and high. At high frequency, the Voc decreased and the Rd increased signifcantly. This was attributed to the local heating effect in the stator due to the increase in the current density. As a result, the FP produced zero output current in this regime. The AC voltage waveforms measured across the stators in different frequency regimes were very different in shapes and amplitudes. Therefore, these waveforms can be used to identify the operating frequency regime of the FP. At some operating frequencies in the mid frequency regime, bi-stable operating modes were observed, each mode resulted in different output parameters. The Gen 4 FP was constructed in this project. It was cooled via thermal conduction method using a cryorefrigerator system. It had an axial-symmetric stator design where the shape of the stator is cylindrical. The width of the stator was considerably larger compared with the Gen 1 and Gen 2 FPs. The experiment objective was to investigate whether this design would produce a DC current, and then characterise the FP performance at different operating temperatures. The experimental results showed that the time-averaged DC output voltage of the Gen 4 FP was much higher compared with the Gen 1 and Gen 2 FPs. The reason is that it produced a DC output voltage for almost the entire rotor cycle. The experimental results also indicated that the Gen 4 FP has the capability to produce output currents in the kA range.</p>

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Impact of Magnet Geometry on Output of a Dynamo-Type HTS Flux Pump

Cited by 42 publications

References 16 publications

Mechanism of the High- Tc Superconducting Dynamo: Models and Experiment

Mechanism of the High- Tc Superconducting Dynamo: Models and Experiment

Modelling the Frequency Dependence of the Open-Circuit Voltage of a High-T _c Superconducting Dynamo

Current-pumping performance of axial-symmetric superconducting dynamo designs

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Impact of Magnet Geometry on Output of a Dynamo-Type HTS Flux Pump

Cited by 42 publications

References 16 publications

Mechanism of the High- Tc Superconducting Dynamo: Models and Experiment

Mechanism of the High- Tc Superconducting Dynamo: Models and Experiment

Modelling the Frequency Dependence of the Open-Circuit Voltage of a High-T c Superconducting Dynamo

Current-pumping performance of axial-symmetric superconducting dynamo designs

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Modelling the Frequency Dependence of the Open-Circuit Voltage of a High-T _c Superconducting Dynamo