Operating modes of high-Tc composite superconductors and thermal runaway conditions under current charging

V. R. Romanovskii, Kazuo Watanabe

Research output: Contribution to journalArticlepeer-review

6 Citations (Scopus)

Abstract

The operating thermal and electric modes of a high-Tc superconducting composite in partially and fully penetrated states induced by the charging current are investigated. They were studied under conditions in which the current charging rate, the volume fraction of the superconductor in a composite or the temperature of the cooling bath were changed. The transient behaviour of the voltage-current dependence, which is characteristic during stable and unstable increases in electric field inside the composite under a continuous current charging, is discussed. Simulations were done using zero- and one-dimensional steady and unsteady thermoelectric models with a power equation describing the virgin voltage-current characteristic of a superconductor. It is found that some thermoelectric trends underlie the shape of the voltage-current characteristic of the high-Tc superconducting composite. These have to be considered during experiments in which the critical or quench currents are defined. First, in the initial stage of the fully penetrated regime (in the low voltage range), the electric field distribution does not have a uniform character. These states depend on the volume fraction of the superconductor and the current charging rate: the higher these quantities, the higher the heterogeneity of the electric field. Second, during the stable over-critical regime (in the high voltage range) occurring in complete penetration modes, the evolution of the electric field may depend on the relevant temperature increase of a composite according to the corresponding increase in its temperature-dependent heat capacity. Consequently, the shape of the voltage-current characteristic of a composite high-Tc superconductor during continuous current charging, both before and after thermal runaway, has only a positive slope. Moreover, it is proved that the growth of the fully penetrated part of the voltage-current characteristic becomes less intensive when the current charging rate or the coolant temperature increase. That is why the voltage-current characteristic of a high-Tc superconductor cannot determine the boundary of onset of thermal runaway. It is also confirmed that there is a thermal degradation mechanism of the current-carrying capacity of the composite. In particular, according to this mechanism, the quench currents do not increase proportionally to an increase in the amount of superconductor in a composite.

Original languageEnglish
Pages (from-to)541-550
Number of pages10
JournalSuperconductor Science and Technology
Volume19
Issue number6
DOIs
Publication statusPublished - 2006 Jun 1

ASJC Scopus subject areas

  • Ceramics and Composites
  • Condensed Matter Physics
  • Metals and Alloys
  • Electrical and Electronic Engineering
  • Materials Chemistry

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