Numerical Simulation on AC Loss in REBCO Stacks and Coils Carrying Non-Sinusoidal Currents

AC loss is a critical issue for high-temperature superconducting (HTS) applications. Earlier studies have focused on ac loss in HTS conductors carrying sinusoidal currents. However, HTS conductors in some applications carry non-sinusoidal currents, and hence it is essential to study ac loss under those conditions. This study presents simulated ac loss of a REBCO stack and coil winding carrying currents with square, trapezoidal, and triangular waveforms. The simulation method is based on the T-A formulation implemented in COMSOL Multiphysics 6.0. AC loss dependence on frequency and n-value is also investigated. The simulation results show ac loss varies with current waveforms for both the stack and coil winding - loss magnitude is largest under square waveform, followed by trapezoidal, sinusoidal, and triangular waveform. Surprisingly, ac loss of the stack decreases with increasing frequency as f-2/n, while f-1/n for the coil winding. The difference between the ac loss values in the stack and coil winding under different current waveforms becomes smaller with increasing n-value. With an infinitely large n-value, the difference in the ac loss values for all different waveforms may disappear, as the critical state model suggests.