Simulation of ac loss in Roebel coated conductor cables

Roebel cables are a promising concept for high-current coated conductor cables with low ac loss. In order to optimize their design, simulations are necessary. In this paper we compute the field and current distribution and the ac loss due to either a transport current or an applied magnetic field. We distinguish between the coupled and uncoupled situations. These situations correspond to the limits of low and high resistance between strands in one transposition length, respectively. We perform the simulations with two different methods. One method assumes the critical-state model for the superconductor and calculates the current distribution by minimizing the magnetic energy variation; the other describes the superconductor with a power-law resistivity and uses the finite-element technique for solving the problem. We found that the results from both models agree with each other. Moreover, the coupling strongly influences the current distribution for all cases, as well as the magnetization loss. However, the effect on the transport loss is small. In conclusion, simulations are necessary in order to predict the loss reduction caused by the strand transposition in a Roebel cable. Our simulation methods are useful for these predictions.