Acceptable coupling losses in coated conductors at industrial frequencies without twisting the superconducting stripes

Abstract

The author calculates precisely the induced currents in striated YBa2Cu3O7 coated conductors covered partially by segmented pieces of normal metal, connecting the individual superconducting stripes. It is shown that the induced current density is below the critical current density of the superconducting stripes and the coupling losses are acceptable low, ensuring in addition sufficient current sharing between the stripes. Thus, the proposed structure can be applicable at ac conditions without twisting procedure. The ratio of the current closed between the normal plates to the current flowing in the superconducting stripes and the losses in the substrate are also discussed. The total current flowing through the whole length of the superconductor, which has to be closed at the ends, is also acceptable low. In addition, the frequency range, in which the magnetic flux can fully penetrate both between the stripes and into the normal segments, is given.

Acceptable coupling losses in striated coated conductors or twisted cables ensuring current sharing between superconducting filaments

“…In this paper, we show that the system of small normal plates suggested in [33,34] can be very effective at enabling current sharing for twisted structures (classical low temperature, as well as high T c cables). This should be very important for bismuth strontium calcium copper oxide (BSCCO) samples with almost isolated filaments and low CLs [36,37], or Roebel samples with small CLs [38].…”

“…For practical applications of the NM plates, the induced current density j s should not exceed the critical current density of the superconductor at any point. For YBCO CCs, the results from [34] could be applied. For classical twisted cables, the induced current density is greatest on the edges, just as for CCs.…”

“…By partial coating of the tapes with segmented pieces of NM, the CLs should be held at an acceptable level even at industrial frequencies [33,34]. The induced currents may close partially in loops between the NM plates, in analogy to the currents flowing at the crossing points of twisted superconducting filaments or strands.…”

“…The distance between the NM segments plays an analogous role to the twist pitch in the twisted structure. The induced current density in the superconductor could be below j c even at industrial frequencies [34]. To test these ideas, the CLs of finite striated YBCO samples with different positions for the NM plates were used [35].…”

“…The basic applicability of the model is that the magnetic field due to the induced currents is negligible with respect to the applied magnetic field. The corresponding restrictions for the allowed frequency are not very critical for NM plate properties [34].…”