Study on AC Losses and Influencing Factors of Three-Phase Coaxial HTS Cable Under Harmonic Current

The ac loss characteristics of a three-phase coaxial high-temperature-superconducting (HTS) cable with copper protective layers structure in a harmonic environment are studied using finite-element analysis based on the H-formulation. We explored the effects of modifying the transmission current amplitude, harmonic current phase difference, former, and protective layer material on the cable's ac losses. The results demonstrate that the total losses of the cable are primarily caused by Eddy currents created in the metal layers. The HTS layers' transport ac loss is most significant in the B phase and most minor in the C phase, and it is mostly unaffected by the harmonic order. Still, it increases with the amplitude of the fundamental transmission current. When the total harmonic distortion is increased while the fundamental transmission current amplitude remains constant, the transport ac loss increases monotonically, with the fifth harmonic having the most significant impact and the seventh having the least. In contrast, the Eddy current loss positively correlates with the harmonic order. On the other hand, the existence of copper protective layers makes the loss of each layer converge to a constant value with the increase of harmonic order, thus reducing the effect of phase on the loss. In addition, the transport ac loss of the HTS layers is increased, and the protective layer's Eddy current loss is decreased by increasing the resistance of the protective layers. Changing the former material impacts the distribution of Eddy current loss in the cable's metal layers, but the overall losses are only slightly impacted.