Potential Electric Power Applications for Magnesium Diboride
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Potential Electric Power Applications for Magnesium Diboride Paul M. Grant Electric Power Research Institute (EPRI) Palo Alto, CA 94304, USA ABSTRACT The newly discovered superconductor, MgB2, has significant potential for a number of electric power applications, even though its critical temperature, TC, is “only” 39 K. In recent months, there has been rapid improvement in its critical state parameters, JC and H*, properties crucial to deployment in power devices, which now rival NbTi at 4.2 K, and equal or surpass many of the high temperature superconducting copper oxide perovskites in the 20 – 25 K range. Moreover, substantial progress has been achieved in realizing wire embodiments that appear economically scalable to commercial production. In this paper, we will review several opportunities to exploit these developments for transformer and electric cable applications, and hint at the possibility of a novel and visionary power delivery system centered on an MgB2-based dc cable cooled by gaseous or liquid hydrogen supplying both electrical and chemical energy to the end user. INTRODUCTION “Advances in superconductivity begin with the empirical search for new materials.” Thus commenced the historic 1986 paper by Bednorz and Mueller announcing the discovery of “high temperature superconductivity” in the family of layered copper oxide perovskites [1]. However, it is occasionally fruitful to closely examine low temperature transport data measured on old ones. This is just what happened during January, 2001, in Japan when a group at AoyamaGakuin University, while investigating the properties of an titanium-magnesium-boron ternary compound in search of magnetic or superconducting behavior noticed trace superconductivity at 39 K in an impurity phase subsequently shown to be MgB2 [2]. In fact, there was even an indication of possible superconductivity in MgB2 that went unrecognized in 1957 in published low temperature specific heat measurements [3]. It is difficult to imagine how differently many applications to both power and electronics would have evolved had MgB2 superconductivity begun development in the 1950s. Within several months following its discovery, a widely accepted theoretical consensus arose that MgB2 was probably the penultimate strong coupled electron-phonon superconductor whose intrinsic properties behave as predicted by extensions of the Bardeen-Cooper-Schrieffer formalism advanced in the 1960s and 70s [4]. At the same time attention began to focus on the applications potential within MgB2 in spite of its relatively low transition temperature of “only” 39 K. One of the earliest indications of promise was the apparent absence of “weak links” between micro-crystals or grains of the material, the Achilles’ Heel of the HTS copper oxides which limit their critical current and magnetic field performance, key parameters for power applications [5]. However, early measurements also indicated a low value of the irreversibility field relative to the upper critical field resulting from thermally activated flux flow
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