Study on Electromagnetic Thermal Characteristics of Stacked REBCO Tapes Under Alternating Current with DC Bias

In practical applications, high-temperature superconducting (HTS) cables or magnets may carry AC with DC bias, such as in superferric magnets, which can increase the AC loss of the cables or magnets. When the DC bias current is high, the resulting high loss can lead to a significant temperature rise in the cable or magnet and may even cause quench. Furthermore, different waveforms of the alternating current also result in different losses and temperature rises. Therefore, it is essential to investigate the AC loss of the cable under different current waveforms and DC bias levels using an electromagnetic-thermal coupling method. In this paper, an electromagnetic-thermal coupling model is used to investigate the AC loss and temperature rise characteristics of four stacked REBCO tapes under four typical current waveforms and various DC bias levels. The actual multilayer structure of REBCO tapes is considered in the numerical simulation, which facilitates the analysis of current distribution among different layers and its contribution to the total loss of the stacked cable. The results show that under zero DC bias or a small DC bias (0.1I_dc), the square-wave current yields the largest AC loss, while the triangular-wave current results in the smallest AC loss. The losses generated by the sawtooth and sinusoidal currents are comparable and intermediate between those of the two aforementioned waveforms. When the DC bias current is moderate (0.5I_dc) and the amplitude of the alternating current is greater than 0.5I_cable, the loss of the cable increases rapidly. The loss generated by the square-wave current is the largest, followed by the sinusoidal current, while the sawtooth and triangular currents produce the smallest losses. When the DC bias current is high (0.9I_dc), even a small amplitude alternating current results in high AC loss in the cable.