Non-uniform current distribution as the cause of false voltage signals in the ac loss measurement on a superconducting cable

Gömöry, Fedor; Frolek, L.; Šouc, J

doi:10.1088/0953-2048/18/5/035

Cited by 18 publications

(14 citation statements)

References 17 publications

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“…Transport AC loss in the 9/2 YBCO Roebel cable can be measured using nine voltage loops shown in figure 3. Each pair of voltage taps is attached to a separate strand and extended to four times the cable width [12,13]. The superficial transport AC losses measured from different voltage loops can disagree with each other and differ from the true transport AC loss of the cable because the current in each strand can contain an outof-phase component.…”

Section: Measurement Methodsmentioning

confidence: 99%

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Transport AC loss characteristics of a nine strand YBCO Roebel cable

Jiang¹,

Badcock²,

Long³

et al. 2010

Supercond. Sci. Technol.

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Transport AC loss in a short length of 9/2 YBCO Roebel cable (nine 2 mm wide strands) is measured. The AC loss data are compared with those in a 5/2 YBCO Roebel cable (five 2 mm wide strands) as well as that in a single strand. All the strands composing the cables and the single strand are insulated and cut from the same stock material. The validity of the measurement method was reconfirmed by results at a range of frequencies. At a wide range of I t /I c , the normalized AC losses in the Roebel cable were around 6.2-6.7 times of those in the single strand. This is less than the nine times predicted for a tight bundle of nine conductors. The normalized transport AC losses in the 5/2 Roebel cable are much smaller than those in the 9/2 Roebel. This should be due to larger superposition of magnetic field in the 9/2 Roebel. The I c of the 9/2 and 5/2 Roebel cables is determined by serial connection of the strands. This eliminates the effect where differing resistances in the current terminations cause uneven current sharing between strands when the strands are connected in parallel.

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Section: Measurement Methodsmentioning

confidence: 99%

“…This is due to the different resistance of each current termination, R i . The superficial transport AC loss measured from each voltage loop per cycle which includes the error, Q t,superficial , can be given as [12,13]…”

Section: Measurement Methodsmentioning

confidence: 99%

Transport AC loss characteristics of a nine strand YBCO Roebel cable

Jiang¹,

Badcock²,

Long³

et al. 2010

Supercond. Sci. Technol.

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“…In general, the current distribution among the different tapes (or strands) may be different. Therefore, placing voltage taps (or D-loops) on one of the strands may lead to an inaccurate evaluation of the losses [18,19]. For this reason, we measured the ac losses by placing the voltage taps on the copper blocks of the current leads.…”

Section: Experimental Setup For Ac Loss Measurementmentioning

confidence: 99%

Transport and magnetization ac losses of ROEBEL assembled coated conductor cables: measurements and calculations

Terzieva¹,

Vojenčiak²,

Pardo³

et al. 2009

Supercond. Sci. Technol.

108

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Many superconductor applications require cables with a high current capacity. This is not feasible with single-piece coated conductors because their ac losses are too large. Therefore, it is necessary to develop superconducting cables with a high current capacity and low ac losses. One promising solution is given by ROEBEL cables. We assembled three ROEBEL cables from commercial YBCO coated conductors. The cables have the same width but a different number of strands, which results in different aspect ratios and current capacities. We experimentally studied their ac losses under a transport current or a perpendicular magnetic field. In addition, we performed numerical calculations, which agree with the experiments, especially for the transport case. We found that in the cables there is good current sharing between the strands. We also found that stacking the strands reduces the magnetization losses. For a given critical current, thicker cables have lower magnetization ac losses. In addition, a conducting matrix is not required for a good current sharing between strands.

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“…The current distribution within the parallel tapes of each phase is then determined by the contact resistances of the individual tapes. This results in an inhomogeneous current distribution, even phase differences occur [6], and the loss determination becomes accidental. For long cables the impact of this effect vanishes, since the inductive contributions to the impedance and their coupling, equal for all tapes, dominate and equalize the currents among the tapes.…”

Section: Introductionmentioning

confidence: 99%