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

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.

Nano-Tech Transformer Cores

This chapter describes optimal characterization of composites and nanocomposites materials that handle traditional transformer cores to design transformer core materials. It attempts to offer new designs for new transformer cores to control the magnetization parameters. This chapter draws attention to theories and effective nanoparticle structure that tackle the characteristics of transformer cores. It further sheds light on the effects of nanoparticles on magnetization loss of transformer core by using individual and multiple magnetic nanocomposites. The forecasting and recommendations of the magnetic characterization are also presented for 1-phase and 3-phase transformer cores.