Losses in Coated Conductors Under Nonsinusoidal Currents and Magnetic Fields

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.

AC losses in thin coated conductors under non-sinusoidal conditions

“…For periodic external magnetic fields and transport currents varying monotonically between their extreme values, the AC losses in a superconducting strip were recently considered in [11,12]. Under non-sinusoidal conditions the waveforms of currents (external magnetic field) are asymmetrical-the current maximum is not equal to the modulus of its minimum.…”

“…Since superconductors possess a strongly non-linear current-voltage characteristic, one can expect a substantial contribution of higher harmonics to AC losses in superconducting elements. Recently, it has been shown [11,12] that the contribution of higher harmonics to AC losses in superconducting bulk and thin film samples can be greater by more than an order of magnitude than in normal-metal samples of the same shape. For example, the 5% third harmonic of a low magnetic field can increase the losses by 20% in a superconducting strip [11], while in normal-metal conductors the contribution of this harmonic is about 2%.…”

Magnetization Loss in HTS Coated Conductor Exposed to Harmonic External Magnetic Fields for Superconducting Rotating Machine Applications

“…In [15], authors explored the AC loss in an HTS coil for wind turbine generators experimentally, under different DC field with AC ripples. In [16]- [17], AC loss in HTS strip under nonsinusoidal current and magnetic field was formulized analytically, only considering harmonic amplitude. In [18], authors studied the total AC loss in a Bi-2223/Ag tape by considering a phase shift between sinusoidal magnetic field and sinusoidal transport current.…”

Influence of field-dependent critical current on harmonic AC loss analysis in HTS coils for superconducting transformers supplying non-linear loads

“…For this purpose, several theoretical studies have been done in order to analytically calculate the AC loss under nonsinusoidal current. In [29][30][31], authors tried to derive a rather simple and straightforward closed form equation based on harmonic orders to calculate the AC transport losses of the HTS tapes. In [32], the AC losses in racetrack coil which is made by YBCO tapes have been measured for nonsinusoidal transport currents with fundamental frequencies up to 1 kHz.…”