In:
Materials Science Forum, Trans Tech Publications, Ltd., Vol. 856 ( 2016-5), p. 32-37
Abstract:
Fault current limiters (FCL) require superconducting (SC) materials which can provide a definite rate of response to a fault event resulting in the SC – normal state reversible transition. The main characteristics determined the material suitability are the critical current density, j c , thermal conductivity and capacity which are strongly determined by manufacturing technology, in particular, of MgB 2 . In the paper we estimate the j c of bulk MgB 2 samples by the vibrating magnetometer and inductive, contactless transformer, method using ring samples. The bulk MgB 2 samples were produced under 30 MPa (hot pressing) and 2 GPa (quasihydrostatic pressing) at 800-1050 о С from different initial ingredients (Mg and B or MgB 2 with and without additions). It is shown that the technology process and initial ingredients strongly influence the distribution of boron-and oxygen-enriched nanosized inhomogenities in MgB 2 matrix, connectivity between SC grains, material porosity and, as result, the SC properties. The transformer method gives the j c in the range from 1.6·10 4 up to 6.3·10 4 A/cm 2 at about 4 K while using magnetometer measurements the j c is estimated from 2.24·10 5 up to 5.1·10 5 A/cm 2 at 10 K in self-magnetic fields. The contradictions in the j c estimated by different methods can be explained by instability of the SC state of MgB 2 , caused by variation of the applied magnetic field. Using the transformer method AC losses per a cycle before quenching for the best materials were estimated around 0.75-1 J / cm 3 , while the power of losses was about 200 W. The FCL model with rings cut out from SC MgB 2 materials prepared using various technologies demonstrated that MgB 2 is a promising material for application in inductive FCLs.
Type of Medium:
Online Resource
ISSN:
1662-9752
DOI:
10.4028/www.scientific.net/MSF.856
DOI:
10.4028/www.scientific.net/MSF.856.32
Language:
Unknown
Publisher:
Trans Tech Publications, Ltd.
Publication Date:
2016
detail.hit.zdb_id:
2047372-2
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