Losses in ac of BSCCO-2223 superconducting monofilament and multifilament tapes at power frequencies
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Losses in ac of BSCCO-2223 superconducting monofilament and multifilament tapes at power frequencies S. Mench, M. Lelovic, T. Deis, and N. G. Eror Department of Materials Science, University of Pittsburgh, Pennsylvania 15261
U. Balachandran Energy Technology Division, Argonne National Laboratory, Argonne, Illinois 60439
P. Haldar Intermagnetics General Corporation, Latham, New York 12100 (Received 14 April 1997; accepted 1 August 1997)
The ac magnetic losses at power frequencies (60 Hz) were investigated for mono- and multifilament Ag-sheathed (Bi, Pb)2 Sr2 Ca2 Cu3 Oy (BSCCO-2223) tapes with similar Ic values at 77 K. The multifilament sample exhibited higher losses than the monofilament under the same conditions. Loss peaks are discussed in terms of intergranular, intragranular, and eddy current losses. Because of BSCCO’s anisotropy, field orientation has a large effect on the magnitude of these peaks, even at relatively small angles. Losses for fields applied parallel to the c-axis of the textured BSCCO grains are larger by over an order of magnitude than those applied perpendicular.
I. INTRODUCTION
High temperature superconductors, such as BSCCO2223, have shown promise for use in applications such as ac power transmission cables. To be of practical use, the power losses that they exhibit must be sufficiently lower than conventional materials so that the savings realized exceed the cost of maintaining the low temperatures required for operation. Multifilament tapes have been developed in an effort to increase the performance of superconducting tapes. Compared with monofilament tapes, the magnitude of ac losses in these geometries is important since they represent ongoing operational costs. The imaginary part, x″, of the complex magnetic susceptibility, x x 0 1 x 00 , is associated with hysteretic ac losses1–3 : Z ° ¢ M dH x 00 H02 ys2m0 d . (1) Ph According to the Bean critical state model, hysteretic losses per cycle of ac magnetic field applied parallel to the slab thickness D are predicted by4,5 : ° ¢ ¢ ° ¢ ° Ph 4WH03 y 3m02 Jc for H0 < H p (2) Ph D WJc H0 fI 2 s2H py3H0 dg 2
for sH0 . H p d , (3)
where W is the slab width, H0 is the amplitude of the applied magnetic field, H* is the magnetic field at which flux completely penetrates the sample, and m0 is the magnetic permeability of free space. It follows from Eqs. (2) and (3) that Ph is characterized by H03 J. Mater. Res., Vol. 12, No. 11, Nov 1997
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dependence when the applied magnetic field does not fully penetrate the sample and by H0 dependence in the regime where the applied magnetic field is greater than the field required for full penetration. It is widely accepted that ac losses in BSCCO tapes are frequency independent at frequencies less than 1000 Hz.5–7 The losses at power frequencies are predominantly hysteretic, with negligibly small eddy current losses.8 Loss peaks in x″ have been attributed to several different mechanisms. Eddy c
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