Abstract

In recent years, compact cables employing second-generation high-temperature superconducting (HTS) wires have been successfully developed, tested and employed. These include the Cross-conductor (CroCo) and Conductor-On-Round-Core (CORC) designs. These types of cables have been primarily developed for magnet applications. However, their compact structure makes them an appealing solution for AC power transmission. One key aspect that determines the applicability of this solution is the level of AC losses, which is essentially determined by the penetration of time-varying magnetic fields in the superconductor material. Since the cables are composed of many superconducting wires, with possibly complex geometrical arrangement, determining the magnitude and orientation of the local magnetic field is not a trivial task. In this contribution we review the origin of the different mechanisms contributing to the losses and of the applicability of analytical tools for estimating the AC losses of the cables. These estimations are compared with the results of 2D and 3D finite-element simulations. In the case of CORC, numerical simulations are also used to confirm and help visualize complex current trajectories inside the superconductor material. The existence of these trajectories was proposed in the 1970s, but their effect on AC losses does not seem to have ever been quantified. Finally, this work discusses possibilities and limitations of practical CroCo and CORC cables for low-loss AC power transmission.