素線間接触抵抗分布のある多重撚りケーブルの素線間結合損失

Abstract

Multi-strand superconducting cables are utilized for large superconducting machines and/or alternative or pulse current devices, such as fusion machines and superconducting magnetic energy storage (SMES) devices. In the numerical evaluation of AC loss, especially inter-strand coupling loss, it is important to establish a model for crossover contact resistance distribution among strands and/or sub-cables. For cables with multiple cabling stages, the contact resistance between two strands (or two sub-cables) changes along the conductor axis due to the related traces. Good contact is attained at locations where they crossover. On the other hand, when they are separated, there is no direct contact between them. The relationship between AC loss and contact resistance was evaluated for a short sample, a 3×3 twisted cable of Cr-plated Nb3Sn strands. The AC loss was measured using the calorie metric method at LHe temperature. The contact resistance between the two strands was also measured for the same sample under the same condition. The contact resistance distribution, which was expected as the result of the contact resistance measurement, was adopted to a numerical model and the AC loss was calculated using the non-uniform constant electric circuit. By comparing the calculated and measured losses, the contact resistance variation model was modified suitably. Finally, the relation between inter-strand coupling loss and contact resistance distribution are discussed from the viewpoint of constitution of the cable using established numerical model.