AC Losses in MgB<sub>2</sub> Wires and Tapes in Frequencies up to 18 kHz

Nikulshin, Yasha; Wolfus, Shuki; Ginodman, Vladimir; Friedman, A.; Tropeano, M.; Grasso, G.; Yeshurun, Y.

doi:10.1109/tasc.2018.2791808

Cited by 4 publications

(5 citation statements)

References 13 publications

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“…For the multifilamentary wire at frequencies above ∼10 3 Hz, the eddy currents in the nonsaturated magnetic sheath dominate the filament losses and become the most significant heat source. These findings are in good agreement with results obtained experimentally [13,14]. Upon decreasing permeability due to saturation, the eddy currents produced in the sheath decrease accordingly.…”

Section: Discussionsupporting

confidence: 92%

“…First, the wire is in a self-field state, carrying either AC current or DC with superimposed AC currents. The AC current of 8 A rms was chosen to be within the range used in previous experiments [13,14], while convenient and sufficient for modelling yet far from the critical current. This case is representative of cables and current leads in general use.…”

Section: Model Detailsmentioning

confidence: 99%

“…In this section we analyze the AC losses in the common case where AC current is superimposed on DC current. Specifically, we select here 40 A DC and 8 A rms AC currents, to match the values in our previous experimental studies [13,14]. For this relatively low DC bias value the current flows in the outer filament layer without fully penetrating the filaments.…”

Section: Biasmentioning

confidence: 99%

“…AC losses in superconducting materials are a well-studied phenomenon [10][11][12]. Superconducting wires, especially those with a magnetic sheath, are less explored because of the increased complexity due to the nonlinear magnetic nature of the filaments and the sheath and their mutual coupling [13][14][15][16]. Moreover, most studies of AC losses in superconducting wires focus on relatively low frequencies, of up to several hundred Hz [17][18][19][20].…”

Section: Introductionmentioning

confidence: 99%

“…The simulations show clearly that the total AC losses depend strongly on the magnetic properties of the wire matrix and sheath. In particular, the eddy currents in the Monel matrix are enhanced [13,14], and its high permeability changes the magnetic field penetration pattern inside the superconducting filaments, contributing to additional hysteresis loss in the superconducting material itself.…”

Section: Introductionmentioning

confidence: 99%

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Effect of magnetic sheath on filament AC losses and current distribution in MgB₂ superconducting wires: numerical analysis

Nikulshin¹,

Yeshurun²,

Wolfus³

2019

Supercond. Sci. Technol.

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Finite element method (FEM) analysis is employed to study and compare AC losses in a wide frequency range in two MgB 2 superconducting wires in self-field and in the presence of external AC field. The modelled wires, of the same external dimensions, are mono-and 36-superconducting filaments embedded in either magnetic Monel or a nonmagnetic metallic wire sheath. We demonstrate that in a multifilamentary wire in self-field the Monel sheath serves as a 'pole piece' at the filament outer surface and alters local magnetic fields, current flow and AC losses distribution within the filament. In comparison with the nonmagnetic sheath with the same electrical conductivity, AC current in the wire with the magnetic sheath penetrates significantly deeper into the filaments and AC losses in the filament and in the magnetic sheath increase significantly. In contrast, the symmetry of the monofilament wire makes the current and loss distributions in the filament practically indifferent to the sheath composition. Still, losses in the magnetic sheath are much higher than in the nonmagnetic sheath due to increased flux dynamics. The application of DC current, on which the AC current is superimposed, sharply reduces the AC losses in the magnetic sheath material due to the drop in its permeability. Filament losses are also reduced in the presence of DC current, but to a much lesser extent. Results also show that in the kHz frequency range, the magnetic permeability of the sheath increases the skin effect in both the wire and filaments complex. As a result, at such frequencies, a significant portion of the current is carried by the metallic part of the wire instead of the superconductor, contributing to a further increase in losses. The analysis also shows that in the presence of external AC magnetic field, the Monel can provide magnetic shielding for inner filaments, thus reducing coupling effects between filaments. However, if magnetically saturated by the DC current, the Monel behaves quite similarly to a nonmagnetic sheath.

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Section: Discussionsupporting

confidence: 92%

Section: Model Detailsmentioning

confidence: 99%

Section: Biasmentioning

confidence: 99%