Eddy current loss in Ag-sheathed BSCCO tapes in the AC transport regime

Abstract

Experimental investigations on Ag-sheathedBSCCO tapes show that losses in the ac-current transport regime are not of purely hysteretic nature. A contribution due to the eddy currents in the silver matrix is present and detectable in the low current limit. I n the present paper we extend an existing model in order to account for this contribution. The tapesuperconducting core is regarded as a strip or as an ellipse. The expressions we obtain are analyzed and compared to experimental data.Iiirkx Terms-AC losses, BSCCO tape, eddy currents, silver matrix.

Transport ac loss in a long cylinder with a hard superconducting core and normal conducting shell

“…The (I m /I c ) 2 behaviour found in [7,19] is similar to ours. In contrast to the situation of (I m /I c ) 6 dependence, we can conclude from the derivation made in section 4.3 for the lowθ 2 low-I m /I c limit that the (I m /I c ) 2 dependence comes from a constant effective conductance of the normal conducting region where the normal current flows and a flux averaged over the same region to be proportional to i.…”

“…If the metal strip is much wider than the superconductor, the ac loss in the metal will be proportional to (I m /I c ) 2 [19]. Later, in order to explain their experimental ac loss of Ag-sheathed Bi-2223 tapes, Tebano et al modified Muller's model by replacing the attached metal strip by two metal blocks connected to both edges of Norris' superconducting strip or ellipse [7]. A (I m /I c ) 2 dependence was also obtained in this case.…”

“…θ 2 =µ 0 σ ωr 2 0 being a dimensionless frequency. Its general solution is H (r) = aJ 1 (kr) + bY 1 (kr), (7) from which the axial current density J (r) in the shell is derived using the Ampère law as…”

“…Since the volume fraction of Ag is quite high (typically about 0.7) and its resistivity at 77 K is quite low, ρ = 3 × 10 −9 m [5], there also could be an appreciable loss resulting from the normal currents flowing through the Ag matrix when the frequency is increased. Some experimental results show that the ac loss per cycle of such tapes may increase with increasing frequency, which has been explained by some eddy-current concepts or models [6,7]. In order to analyse experimental results and to help the design of superconducting elements, a deeper understanding of the frequency-dependent ac loss considering both super and normal currents is necessary.…”

Higher harmonics in the voltage on a superconducting wire carrying AC electrical current

“…In the cases when the \loss behaviour" did not appear in agreement with theoretical predictions, several phenomena have been proposed to contribute to the observed losses. Most of them are of linear eddy-current like in nature, with no contribution to higher harmonics of the voltage signal [15,16]. This means they do not a®ect our predicted results of the harmonic composition of that part of the voltage that is linked with irreversible°ux penetration into the superconductor bulk.…”