Losses in Coated Conductors Under Nonsinusoidal Currents and Magnetic Fields

Abstract

The study of AC losses in superconducting wires and tapes is usually restricted by consideration of applied sinusoidal currents and/or magnetic fields. However, currents in electric power systems contain a wide variety of harmonics. The currents become strongly nonsinusoidal in the operation of converters and nonlinear reactors, and during transient and overload conditions. Recently it has been shown that the contribution of higher harmonics to AC losses in superconducting bulk and thin film samples can be tens times larger than in normal-metal samples of the same form, and the 5% harmonic can increase the losses by up to 20%. Here we report the results of an analysis of the influence of higher harmonics of the current and magnetic field on AC losses in coated conductors. Analytical expressions are obtained in the framework of the critical state model, neglecting the response of the normal-metal substrate and stabilization layers. Losses in the superconducting and normal-metal parts of a coated conductor are compared for various designs of the conductor. It is also shown that the 5% third current harmonic can increase the losses in the normal-metal parts by up to 60%. This increase is caused by a nonlinear response of the superconducting layers and should be taken into account in the determination of the optimal operation regimes of superconducting devices.