Losses in coated conductors under non-sinusoidal currents and magnetic fields

TL;DR

This paper analyzes how non-sinusoidal currents and magnetic fields, especially higher harmonics, significantly increase AC losses in coated superconducting conductors, impacting their optimal operation.

Contribution

It provides analytical expressions for AC losses under non-sinusoidal conditions, considering higher harmonics, and compares losses in superconducting and normal-metal parts of coated conductors.

Findings

Higher harmonics can increase AC losses by tens of times in superconductors.

A 5% third harmonic can raise normal-metal losses by up to 90%.

Non-linear response of superconducting layers is crucial for device optimization.

Abstract

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 non-sinusoidal at the operation of converters, non-linear 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 the 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 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 90%. This increase is caused by non-linear response of superconducting layers and should be taken into account at determination of the optimal operation regimes of superconducting devices.