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.