Experimental evaluation of AC losses in superconducting multifilamentary wires for 50/60 Hz use exposed to a magnetic field with arbitrary angle with the wire axis

摘要

In multiple twisted superconducting cables exposed to an external AC transverse magnetic field, a component of magnetic field parallel to the strand axis due to the twisting structure of the cables causes an additional AC loss (longitudinal AC loss) in the strands. The authors experimentally evaluate the longitudinal AC loss by an equivalent measurement with short samples of the strands exposed to an oblique magnetic field to the strand axis. The total loss obtained at 60 Hz was equivalent to a direct sum of the hysteresis loss, the coupling-current loss for the transverse component and the additional loss for the longitudinal one. In triple twisted superconducting cables composed of insulated strands, measured AC losses could be also quantitatively explained in the same manner as for the short samples. These results suggest that the longitudinal loss may be dominant in an AC magnetic field with relatively large amplitude along with the coupling-current losses inside and among strands. The authors also discuss an optimum condition for the twist pitch of the strand to reduce the total AC loss of the strands in the cable.