The dynamic resistance of YBCO coated conductor wire: effect of DC current magnitude and applied field orientation

Abstract

Dynamic resistance, which occurs when a HTS coated conductor carries a DC current under an AC magnetic field, can have critical implications for the design of HTS machines. Here, we report measurements of dynamic resistance in a commercially available SuperPower 4 mm-wide YBCO coated conductor, carrying a DC current under an applied AC magnetic field of arbitrary orientation. The reduced DC current, It/Ic0, ranged from 0.01 to 0.9, where It is the DC current level and Ic0 is the self-field critical current of the conductor. The field angle (the angle between the magnetic field and the normal vector of the conductor wide-face) was varied between 0° and 90° at intervals of 10. We show that the effective width of the conductor under study is ~12% less than the physical wire width, and we attribute this difference to edge damage of the wire during or after manufacture. We then examine the measured dynamic resistance of this wire under perpendicular applied fields at very low DC current levels. In this regime we find that the threshold field, Bth, of the conductor is well described by the non-linear equation of Mikitik and Brandt. However, this model consistently underestimates the threshold field at higher current levels. As such, the dynamic resistance in a coated conductor under perpendicular magnetic fields is best described using two different equations for each of the low and high DC current regimes. At low DC currents where It/Ic0  0.1, the non-linear relationship of Mikitik and Brandt provides the closest agreement with experimental data. However, in the higher current regime where It/Ic0 ≥ 0.2, closer agreement is obtained using a simple linear expression which assumes a current-independent penetration field. We further show that for the conductor studied here, the measured dynamic resistance at different field angles is dominated by the perpendicular magnetic field component, with negligible contribution from the parallel component. Our findings now enable the dynamic resistance of a single conductor to be analytically determined for a very wide range of DC currents and at all applied field angles.

Dynamic Resistance Measurement in a Four-Tape YBCO Stack With Various Applied Field Orientation

“…(3). For a single coated conductor, when It is very small, the Bep value increases due to the increase in the shielding currents [27]. As a result, Bth values for the single conductor show good agreement with Eq.…”

“…(3) at very small It. Same thing might happen in the conductors in the stack [27]. The results for all the tapes are similar in all cases, therefore we only show T1 result here.…”

Study of the magnetization loss of CORC® cables using a 3D T-A formulation

“…where E0 = 1×10 -4 V/m and n = 31 for the tape used in this study. Jc is the critical current density and its field dependence is expressed as follows [51]: The magnetization loss energy induced in superconducting layers is calculated by [52][53][54][55][56]:…”

Dependence of Dynamic Loss on Critical Current and n-Value of HTS Coated Conductors

“…YNAMIC loss and dynamic resistance have aroused widespread concern recently in the domain of hightemperature superconductors (HTS) [1]- [4]. It is generated inside the superconductor carrying direct current (DC) in an alternating magnetic field environment.…”