Self-field effect and current-voltage characteristics of a.c. superconductors

High temperature superconducting (HTS) conductor-on-round-core (CORC ® ) cables have been developed for use in power transmission systems and large high-field magnets. The use of highcurrent conductors for large-scale magnets reduces system inductance and limits the peak voltage needed for ramped field operation. A CORC ® cable contains a large number of RE-Ba 2 Cu 3 O 7−δ (RE=rare earth) (REBCO) coated conductors, helically wound in multiple layers on a thin, round former. Large-scale applications, such as fusion and accelerator magnets, require current ramp rates of several kilo-Amperes per second during pulsed operation. This paper presents results that demonstrate the electromagnetic stability of a CORC ® cable during transient conditions. Measurements were performed at 4.2 K using a 1.55 m long CORC ® cable in background fields of up to 19 T. Repeated current pulses in a background field of 19 T at current ramp rates of up to 67.8 kA s −1 to approximately 90% of the cable's quench current at that field, did not show any sign of degradation in cable performance due to excessive ac loss or electromagnetic instability. The very high current ramp rates applied during these tests were used to compensate, to the extent possible, the limited cable length accommodated by the test facility, assuming that the measured results could be extrapolated to longer length cables operated at proportionally lower current ramp rates. No shift of the superconducting transition to lower current was measured when the current ramp rate was increased from 25 A s −1 to 67.8 kA s −1 . These results demonstrate the viability of CORC ® cables for use in low-inductance magnets that operate at moderate to high current ramp rates.

Section: Measurements Performed In 19 T Background Fieldmentioning

confidence: 99%

Behavior of a high-temperature superconducting conductor on a round core cable at current ramp rates as high as 67.8 kA s⁻¹in background fields of up to 19 T

Michael

Bromberg

Laan

et al. 2016

“…Furthermore, in addition to the AC loss, the shape of the voltage signal in the coil is also interesting for both the understanding of the loss mechanisms and applications [13][14][15][16][17][18][19].…”

Section: Introductionmentioning

confidence: 99%

Theoretical and experimental study of AC loss in high temperature superconductor single pancake coils

Šouc

Pardo

Vojenčiak

et al. 2008

The electromagnetic properties of a pancake coil in AC regime as a function of the number of turns is studied theoretically and experimentally. Specifically, the AC loss, the coil critical current and the voltage signal are discussed. The coils are made of Bi 2 Sr 2 Ca 2 Cu 3 O 10 /Ag (BiSCCO) tape, although the main qualitative results are also applicable to other kinds of superconducting tapes, such as coated conductors. The AC loss and the voltage signal are electrically measured using different pick up coils with the help of a transformer. One of them avoids dealing with the huge coil inductance. Besides, the critical current of the coils is experimentally determined by conventional DC measurements. Furthermore, the critical current, the AC loss and the voltage signal are simulated, showing a good agreement with the experiments. For all simulations, the field dependent critical current density inferred from DC measurements on a short tape sample is taken into account. 1 In fact, this condition is not strictly sufficient. The external field must be much larger than the self field of a stack made of as many tapes as those in the radial direction when the radial field dominates the AC loss (and equivalent with the axial direction when the dominant is the axial field).

“…When the experimental conditions allow us to neglect the self-field magnetic loss, P mag , with respect to the resistive loss, P res , the voltage measured on the wire in AC conditions should follow the dependence (7) derived originally for DC transport. The same conclusion has been tacitly used in several experimental works investigating the current-voltage curves in AC [8,9] and nicely documented in [10]. The experimental data of the latter work could be taken as the experimental confirmation of the validity of the expression (6) in the description of the AC current-voltage curve.…”

Section: A Model For the Calculation Of Resistive Ac Lossmentioning

confidence: 57%

Resistive losses in a high-T_cwire carrying AC current larger thanI_c

Gömöry

Janiková

Šouc

2002

A procedure that allows the calculation of the resistive AC loss in a multifilamentary superconducting wire carrying AC transport current was developed. This loss mechanism, detected by the appearance of a finite drop of electrical potential along the wire, is significant when considering transport currents with amplitudes that exceed the critical current of the wire. The physical model behind our calculation for a common wire, that contains superconducting filaments in a metallic matrix, is the simple parallel combination of two elements: the superconductor standing for the properties of all the filaments, and the normal resistor representing the matrix. The total current carried by two parallel conducting paths is easily calculated for any imposed potential drop. But the inverse task-calculation of the potential drop that would force a defined current to be transported-requires us to resolve a nonlinear equation. We show how it is possible to evaluate the resistive loss by a procedure that needs to perform the root-finding operation in one point of the cycle only. The numerical integration is still necessary, but now it is easily performed because the integrand is explicitly defined. The procedure was successfully tested by comparison with experimental data.