In some high-temperature superconductor (HTS) applications, such as field-triggered persistent current switches, flux pumps, and field windings of synchronous rotating machines, REBCO coated conductors (CC) carry DC currents under AC magnetic fields. The direct influence of the external AC magnetic field in these applications results in two types of AC losses: magnetisation loss due to the shielding current and dynamic loss due to the interaction between the AC field and DC transport current. The summation of these two loss components is referred to as the total loss. AC loss causes a parasitic heat load which has a significant impact on the sizing of the cryogenic system, whilst the operating temperatures for the applications could vary over a wide range and the amplitude of the external AC magnetic field could be large. As such, to successfully design systems, the behaviour of these losses under different conditions must be known. Current literature has focussed on experimental and simulation results of ReBCO CC for operating temperatures between 77 K – 65 K and magnetic fields up to 100 mT. However, there have been no reports for lower temperatures and magnetic flux density above 100 mT.

In this work, dynamic resistance and total loss in a 4 mm wide Superpower ReBCO CC are numerically investigated for various operating conditions using the 2D finite element modelling method based on the T-A formulation using COMSOL Multiphysics. Simulations are carried out for temperatures ranging from 30 K to 50 K under perpendicular magnetic fields up to 500 mT with differing values of the DC transport current. The dependence of the critical current of the REBCO CC on the magnitude of the applied magnetic field, field angle, and temperature is considered in order to understand the influence of the critical current on the dynamic resistance and total loss. The simulation results are then compared with the analytical values. Furthermore, the current density distribution and magnetic field penetration profiles are analysed to describe the relationship between the dynamic resistance and total loss and those parameters.

Acknowledgement
This work was supported by the New Zealand Ministry of Business, Innovation and Employment under the Advanced Energy Technology Platform program “High power electric motors for large scale transport” contract number RTVU2004.

Keywords: HTS, Dynamic resistance, Total loss, AC loss