Total loss measurement and simulation in a REBCO coated conductor carrying DC current in perpendicular AC magnetic field at various temperatures

Abstract

In many high-temperature superconducting (HTS) applications, HTS coated conductors carry DC currents under external AC magnetic fields. There are two AC loss mechanisms in this situation: magnetization loss due to the external magnetic field and dynamic loss due to the interaction between the DC current and the external magnetic field. The sum of these two loss components is referred to as total loss. In this work, the total loss in a 4 mm wide REBCO coated conductor is measured under perpendicular AC magnetic fields up to 105 mT at 77 K, 70 K, and 65 K, with reduced DC current level, i (I dc/I c0), from 0.025 to 0.98, where I dc is the transport DC current value and I c0 is the self-field critical current of the coated conductor at each temperature. The experimental results show a good quantitative agreement with an analytical equation for each loss component, as well as 2D finite element modelling (FEM) results from H -formulation. For any given temperature, we observe that the total loss is mostly dominated by magnetization loss at i< 0.2, while dynamic loss makes a comparable, even greater contribution to total loss at i > 0.5. Electromagnetic analysis from the FEM modelling shows the evolution process of total loss, where the dynamic loss region and magnetization loss region vary across the conductor width at high magnetic fields or high DC current level. The simulation results also reveal the superposition of (positive) DC current and the anti-parallel (negative) shielding current, which occurs at high DC current level. The superposition drives the current density of one conductor edge to subcritical stage, and it leads to one-sided loss generation in each half-cycle. Our results provide a valuable reference for total loss behaviours in REBCO coated conductors.

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.…”

“…When B m < 10 mT, the simulated Q m,i values are one to two order magnitude higher than Q m,0 for 0.3 ≤ i ≤ 0.9, whilst Q m,i values become smaller than Q m,0 at high-B when i > 0.5. The behaviors have been observed in previous studies for a single REBCO tape or a three-tape REBCO stack [14], [16]. At low current and low field, the current-carrying capacity of HTS tape is large enough to accommodate both the DC current and the shielding current, and Q m,i is determined by the amplitude of external magnetic field and DC current nearly has no influence on Q m,i .…”

“…At i = 0.9, Q dyn nearly overlaps with Q total (see Fig. 13 (d)) due to the dominance of the flux-flow loss, and similar loss behaviors have been observed in single REBCO tapes and a three-tape REBCO stack [14], [15], [18]. Fig.…”

“…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]. 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].…”