Investigation of Demagnetization in HTS Stacked Tapes Implemented in Electric Machines as a Result of Crossed Magnetic Field

Baghdadi, Mehdi; Fagnard, Jean-François; Zhang, Min; Wang, W; Coombs, Tim

doi:10.1109/tasc.2014.2372873

Cited by 36 publications

(25 citation statements)

References 16 publications

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“…They also show that the decay constant increases roughly in proportion to the number of tapes in a stack. These results can explain qualitatively the very slow decay of the magnetisation in refs (6,7). The experimental situation is more complex.…”

Section: Discussionsupporting

confidence: 64%

See 1 more Smart Citation

Demagnetisation by crossed fields in superconductors

Campbell¹,

Baghdadi

Patel

et al. 2017

Supercond. Sci. Technol.

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A study has been made of the decay of the trapped magnetisation in superconductors when exposed to a crossed field. Numerical results have been compared with the theory of Brandt and Mikitik (4) which solves the problem for a thin strip superconductor. FlexPDE with the A formulation and COMSOL with the H formulation were both used. Simulations of a strip with a cross section aspect ratio of 20 showed good agreement with theory both for the case of a transverse field larger than the transverse penetration field and for one smaller. In the latter case the magnetisation saturates as predicted, however the simulations show a slow decay after many cycles. In the case of stacked YBCO tapes the movement of flux lines is very small and the effects of the reversible motion were investigated. This can decrease the decay initially for very thin decoupled tapes, but cause a steady decay after very large numbers of cycles. Simulations on stacked strips showed that the decay constant increased approximately linearly with the number of strips. When combined with the theory for one tape this can explain the very slow decay observed in previous experiments. Experimental results were qualitatively in agreement with theory and simulations but showed some discrepancies. However there are a number of differences between the experimental situation and theory so good agreement is not expected. IntroductionIn most applications of bulk superconductors using trapped fields the bulk will be exposed to external fields which will change in both angle and magnitude. While changes in in magnitude are easily incorporated in the Bean model, changes in angle lead to much more complex situations, in many cases involving flux cutting and force free configurations. However many experimental measurements have shown that in general trapped fields are always reduced by the application of crossed fields and this effect may limit the application of bulk superconductors in electrical machines. Most of the experiments were at relatively high fields compared with the crossed fields and directed at elucidating the physics, rather than practical applications of bulk superconductors in motors and generators. In this paper we consider geometries in which the induced currents are mostly perpendicular to the fields so that the standard Bean model can be applied. One of the first observations was that of Sychev et. al. (1), who applied an oscillating field to a wire carrying a current and observed a DC voltage. Sakamoto et. al. (2) used a thin film carrying a current in an applied field and measured the decay of the trapped magnetisation when a transverse field was applied, as in this paper. They showed that the flux lines pivoted about two points alternately and 'walked' out of the film, a bit like penguins heading for their breeding grounds in the Antarctic. They proposed an approximate theory which assumed a uniform current density in the film. The DC voltage generated by an AC field was termed the 'dynamic resistance' and the clearest explanation of t...

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Section: Discussionsupporting

confidence: 64%

“…However the decay was a factor of five slower than predicted by simulations. Experiments on stacked YBCO tapes showed a remarkably low decay rate, even in cross fields many times larger than the parallel field required to penetrate the YBCO layer (6,7). On the other hand Celebi et.…”

Section: Introductionmentioning

confidence: 99%

Demagnetisation by crossed fields in superconductors

Campbell¹,

Baghdadi

Patel

et al. 2017

Supercond. Sci. Technol.

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“…The results can help understand the behaviour of tilted stacks, which were observed to provide good homogeneity and strength of the field [19]. Similar patterns of currents are observed in magnetic shields, which can be used to decrease demagnetisation [20], especially open magnetic shields made of short pieces of tapes [21].…”

Section: Introductionmentioning

confidence: 60%

Distribution of Trapped Magnetic Flux in Superconducting Stacks Magnetised by Angled Field

Smara

Climente-Alarcón

Glowacki

2019

J Supercond Nov Magn

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Some novel energy applications require the use of complex shapes of stacks of superconducting tapes as trapped-flux magnets. A trapped-flux magnet magnetised in a superconducting motor may experience an angled magnetising field rather than a field normal to its surface. This will affect the trapped magnetic flux distribution. This work presents the results of the numerical and experimental analyses of the stacks magnetised in an angled magnetic field. The finite element model using H-formulation is developed to compute the induced superconducting currents. The measurements are performed on stacks with different thicknesses and with different orientations against a magnetising field. The resulting distribution of the magnetic flux as well as the electric currents is computed, presented and discussed in details. The importance of the observed distribution patterns is assessed in the context of the implementation of such stacks in a fully superconducting electric motor.

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“…Conventional PM blocks with unity recoil permeability were used. Only the 'equivalent' remanent flux density of the blocks was varied to represent the high fields produced by the superconducting bulks [10], [18] or stacks of superconducting tapes [19].…”

Section: Superconducting Machine Designmentioning

confidence: 99%

Stator Design and Performance of Superconducting Motors for Aerospace Electric Propulsion Systems

Manolopoulos

Iacchetti

Smith

et al. 2018

IEEE Trans. Appl. Supercond.

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Hybrid electric propulsion has been identified as a potential solution to the ambitious environmental emissions and noise targets of the aerospace industry. Superconducting machines may be the key component of that topology enabling the high power densities and efficiencies needed in aerospace. Fully superconducting machines, however, are not a mature technology. This paper looks at the different machine design configurations focusing on the stator magnetic circuit of a fully superconducting motor. The motor has been designed for an aerospace distributed fan propulsion motor with an aerospace benchmark specification of 1 MW. The AC fully superconducting machine includes superconducting bulk magnets mounted on a conventional rotor core and an MgB2 superconducting wire wound stator. The AC losses in the stator winding are particularly sensitive to exposure to the main rotor field so different screening solutions were used to shield the superconducting windings from the rotor field. The effectiveness of the screening techniques for the stator coils and the impact on the machine performance and weight were evaluated for different stator designs, such as full stator core and air core with and without flux diverters. Various combinations of pole numbers, diverter geometries and magnetic materials have been checked. Results show that there is a tradeoff between stator iron losses and superconducting losses.

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Investigation of Demagnetization in HTS Stacked Tapes Implemented in Electric Machines as a Result of Crossed Magnetic Field

Cited by 36 publications

References 16 publications

Demagnetisation by crossed fields in superconductors

Demagnetisation by crossed fields in superconductors

Distribution of Trapped Magnetic Flux in Superconducting Stacks Magnetised by Angled Field

Stator Design and Performance of Superconducting Motors for Aerospace Electric Propulsion Systems

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