Comparison of AC-losses of superconducting power cables based on YBCO- and BSCCO-material measured in a setup with serial connection of the tapes
Résumé
For the minimization of AC-losses in a superconducting power cable their experimental determination is highly desirable with respect to the optimization of the design. However measurements on short samples are strongly hampered by the inhomogeneous current distribution between the superconducting tapes. A recently developed experimental setup gets rid of this problem by using a serial connection of the tapes with mutual field compensation of the backwards conductors.
With this experimental method we now obtained first results of AC-losses in a one phase superconducting cable equipped with 22 YBCO-tapes (Superpower SCS 4050, width 4mm, Ic = 112 A). The losses were measured with an s-shaped voltage lead geometry and good reproducibility on the different tapes of the cable. Compared to the losses of a single tape, which are well described with the Norris-model (strip), the specific losses within the cable are reduced by a factor of about two, this in spite of the increased local field. This result is explained with the nearly perfect azimuthal direction of the local magnetic field. In additional experiments we studied the AC-losses for cases in which one or more tapes carry no current, a situation identic to application cases with damaged tapes. As a result the losses in the neighbouring tapes are increased by up to an order of magnitude, due to the increased vertical components of the self-field. This is confirmed by dedicated finite-element method simulations.
Finally the experiments were compared to previous measurements on cables based on BSCCO 2223 tapes. The AC-losses for both materials are comparable, however the increased critical DC-current observed in the 1G – cable configuration could not be confirmed for 2G – cables.