Abstract
AbstractDiameter of the superconducting ac composite strand is small, typically 0.1 mm, because the strand must be twisted in a very short pitch to reduce coupling losses. Therefore, current capacity of the single strand is small and in the range of ∼10 A. In large‐scale electric power apparatus, the conductors must be able to carry large currents and hundreds of these composite strands should be bundled. The composite strand is highly unstable and susceptible to a very small disturbance due to a frictional wire motion because the main matrix of the wire is highly resistive CuNi.For stable operation of an ac superconducting winding, every strand in the bundle cable should be fixed firmly. An effective technique to fix strands is to impregnate the winding by epoxy. In this case, the ac losses in the winding are to be cooled by heat conduction through the epoxy. Therefore, it is important to estimate the temperature rise of the winding to discuss the fact that the epoxy impregnation technique is applicable to the ac superconducting electric power apparatus.In this paper, the mechanism of thermal conduction of the epoxy‐impregnated winding at the 4.2 K region is discussed based on experimental data and the temperature rise of a large‐scale cable bundles by 7 × 7 × 7 strands calculated considering thermal resistivity at the interface between the epoxy and the strand. The calculated value agrees well with the measured value.
Published Version
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