Measurements of AC losses in different former materials

A high temperature superconducting cable may be based on a centrally locate d cylindrical support, a so-called former. If electrically conductive, the former can contribute to the AC losses through eddy current losses caused b y unbalanced axial and tangential magnetic fields. With these measurements we aim at investigating the eddy current losses of commonly used former mat erials. A one layer cable conductor was wound on a glass fibre reinforced p olymer (GFRP) former. By inserting a variety of materials into this, it was possible to measure the eddy current losses of each of the former candidat es separately; for example copper tubes, stainless steel braid, copper brai d, corrugated stainless steel tubes, etc. The measured data are compared wi th the predictions of a theoretical model. Our results show that in most ca ses, the losses induced by eddy currents in the former are negligible. Howe ver, for materials with a low resistivity the eddy current losses may becom e significant, e.g., for high purity Cu or Al. (C) 1998 Elsevier Science B. V. All rights reserved.