Model for electromagnetic field analysis of superconducting power transmission cablecomprising spiraled coated conductors

Abstract

Since the superconductor layers of YBCO-coated conductors are very thin, the acloss of coated conductors is dominated by the magnetic flux density normal tothe conductor face. In cables, most of the normal magnetic flux component isgenerated near gaps between coated conductors. Although the effects of gaps aresignificant, there are few reports on the electromagnetic field analysis of cables withspiral structures carried out while taking the gap effect into consideration. In afinitely long cable with a spiral structure, the electromagnetic field is naturallyperiodic along the cable axis. In a two-layer cable, the simplest period along thecable axis is the least common multiple of the spiral pitches in the inner andouter layers. However, we verified that there is a shorter period, and the sameelectromagnetic field distribution appears in all conductors of the same layer. Usingthese periodicities, we developed a three-dimensional model for the analysis oftwo-layer cables with a spiral structure. Current distributions of cables were analyzedusing this model, and ac losses were calculated. In addition, these results werecompared with ac losses calculated by two-dimensional analysis performed on thecross section of a cable. It was verified that the ac loss in a cable is correctlycalculated by the 2D model when the spiral pitch is long enough. However, in thecase of a tightly twisted cable, the ac losses calculated by the 2D model includesome errors caused by an approximation in which the spiral structure is ignored.