Dynamic resistance and total loss in a three-tape REBCO stack carrying DC currents in perpendicular AC magnetic fields at 77 K

Abstract

In many high-temperature superconducting (HTS) applications, HTS coated conductors carry a DC current under an external AC magnetic field. In such operating conditions, dynamic resistance will occur when the traversing magnetic flux across the HTS conductors. Consequently, AC loss within the superconductors is composed of the dynamic loss component arising from dynamic resistance and the magnetization loss component due to the AC external magnetic field. In this work, the dynamic resistance and the total loss in a three-tape HTS coated conductor stack were measured at 77 K under perpendicular AC magnetic fields up to 80 mT and DC currents (Idc) up to the critical current (Ic). The stack was assembled from three serial-connected 4 mm wide Superpower wires. The measured dynamic resistance results for the stack were well supported by the results from 2D H-formulation finite element modelling (FEM) and broadly agree with the analytical values for stacks. The FEM analysis shows asymmetric transport DC current profiles in the central region of the superconductor. We attribute the result to the superposition of DC currents and the induced subcritical currents which explains why the measured magnetization loss values increase with DC current levels at low magnetic field. The onset of dynamic loss for the stack for low i (Idc/ Ic) values is much slower when compared to that of the single tape and hence the contribution of the dynamic loss component to the total loss in the stack is much smaller than that of the single tape. Dynamic loss in the stack becomes comparable to the magnetization loss at i = 0.5 and becomes greater than the magnetization loss at i = 0.7. Both magnetization loss and dynamic loss in the stack are smaller than those of the single tape due to shielding effects.

Simulation of Dynamic Resistance and Total Loss of HTS CORC Cables

“…when i = 0, from view A, it clearly shows only shielding currents are induced at the edges, as highlighted in black circles where magnetization loss is generated. No current flows in the central region, which is consistent to previous papers [14], [15], [16], [17], [18]. When i = 0.5 and B a = 5 mT, there is no dynamic resistance as shown in Fig.…”

“…At 2 mT, Q m,i grows monotonically with increasing i; Q m,i reaches maximum at i = 0.9 for 10 mT; Q m,i values decrease monotonically once B m ≥ 30 mT. Similar tendency also has been observed in a three-tape HTS stack where the magnetization loss Q m,i behaviors have been explained via remanent magnetization which was determined by the asymmetric internal current distribution (consists of the DC current and the induced shielding currents) in the superconductors [18].…”

“…The difference in Q m,0 values between Cable B, B2 and the spiral tape, Cable A becomes smaller with increasing the amplitude of the magnetic field and ultimately disappears when B m > 90 mT. This is due to the nature of shielding effect that weakens with increasing the magnetic field and completely disappear once the amplitude of the external magnetic field is much greater than the effective penetration field [14], [18].…”

“…To date, many previous works on dynamic resistance and total loss have mainly focused on single HTS coated conductor tapes [12], [13], [14], [15], [16], [17] or stacks [3], [18], [19], [20], [21], [22], [23]. In terms of the operating conditions, the dependence of dynamic resistance and total loss of single REBCO coated conductors on magnetic field/DC current/temperature/frequency have been investigated through experiments [13], [14], [15].…”

“…In terms of the operating conditions, the dependence of dynamic resistance and total loss of single REBCO coated conductors on magnetic field/DC current/temperature/frequency have been investigated through experiments [13], [14], [15]. Dynamic resistance and total loss of a three-tape HTS stack have been measured where both magnetization loss and dynamic loss in the stack were smaller than a single tape due to the shielding effect [18]. Simulations based on 2D H-formulation have studied the dynamic resistance/loss and total loss of single REBCO coated conductors and stacks [16], [17], [21].…”