Inductance of Low-Frequency Small-Scale High-Temperature Superconducting Coils

Numerical simulation is an effective tool for predicting the electromagnetic behavior of superconductors. Recently, a finite element method (FEM)-based model coupling the T-A formulation with an electrical circuit has been proposed: the model presents the superconducting constituent as a global voltage parameter in the electrical circuit. This allows assessing the overall behavior of complex high-temperature superconductor (HTS) systems involving multiple power items, while keeping a high degree of precision on the presentation of local effects. In this work, the applicability of this model has been extended to large-scale HTS applications with hundreds or thousands of tapes by referring to two widely recognized methodologies, multi-scale and homogenization, to improve the computation efficiency. Based on the two approaches, three different models were developed and their effectiveness was assessed using the case study of a 1000 turn cylindrical HTS coil charged by a DC voltage source. The comparison of the calculated global circuit parameters, local field distributions, losses, and computation time proves that the computation efficiency can be improved with respect to a model simulating all HTS tapes, without compromising accuracy. The results indicate that the developed models can therefore be efficient tools to design and optimize large-scale HTS devices used in electrical machines and power grids. Besides, it is found that the inductance of an HTS coil is varied according to the transport current and could even be higher than that of a normal conductor coil with the same geometry. We attribute this result to the superconductor's non-uniform current distribution and relaxation effect during the dynamic process.

Section: Inductance Of Hts Coilsupporting

confidence: 90%

Section: Inductance Of Hts Coilmentioning

confidence: 76%

Coupling electromagnetic numerical models of HTS coils to electrical circuits: multi-scale and homogeneous methodologies using the T-A formulation

Zhou¹,

Santos²,

Ghabeli³

et al. 2022

“…In more detail, the current densities concentrate on the upper and lower edges of the DP coil and exhibit a skin effect (see later in figure 6), and the skin effect becomes even more severe when the transport current is smaller or the current ramping rate is faster. So, the effective region of the HTS tapes to carry the current densities is narrowed to the upper and lower edges of the DP coil, leading to (1) the self and mutual inductances of the HTS tapes changing slightly [73][74][75]; (2) the effective resistance of the HTS tapes are increased, because the current densities are narrowed to concentrate in the effective region, leading to a smaller effective cross-sectional area of the superconducting wire and larger power-law resistivity.…”

Section: Model Validationmentioning

confidence: 99%

Study of the demagnetization behavior of no-insulation persistent-current mode HTS coils under external AC fields by 3D FEM simulation

Zhong,

Wu,

et al. 2024

The no-insulation (NI) winding technique is promising to be applied in the persistent-current mode (PCM) operation of high-temperature superconducting (HTS) coils to provide those advantages. To apply the NI PCM coil, its demagnetization behaviour (i.e., decay of persistent DC current) by external AC field, which occurs in maglev trains, electric machines, and other dynamic magnet systems, is essential to be understood. For this purpose, a 3D FEM model, capturing the full electromagnetic properties of NI HTS coils, is established. This work has studied three kinds of AC fields, observing the impact of turn-to-turn contact resistivity on demagnetization rates, which is attributed to current distribution modulations. Under transverse AC field, the lower contact resistivity attracts more transport current to flow in the radial pathway to bypass the ‘dynamic resistance’ generated in the superconductor, leading to slower demagnetization. Under axial AC field, the demagnetization rate exhibits a non-monotonic relation with the contact resistivity: (1) the initial decrease of contact resistivity leads to concentration of induced AC current on the outer turns, which accelerates the demagnetization; (2) the further decrease of contact resistivity makes the current smartly redistribute to avoid to flow through the loss-concentrated outer turns, thus slowing down the demagnetization. Under the rotating DC field, a hybrid of the transverse and axial fields, the impact of contact resistivity on the demagnetization rate exhibits combined characteristics of the transverse and axial components. Besides, quantitative prediction on the demagnetization rate of NI PCM coil under external AC field is instructive for practical designs and operations, which is tried by this 3D FEM model, and a comparison with experimental result is conducted.

“…At high frequencies, the magnetic field coupling of the transformer coils is more complex, making the magnetic field distribution and current density of the coils difficult to calculate. Additionally, the variation of the current density in the superconducting coil makes the self-inductance of the superconducting coil not a constant value [16,17], and the metal reinforcement layer of the superconducting tape generates considerable eddy current losses at high frequencies [18][19][20]. Due to the special characteristics of superconducting coils at high frequencies, it is inaccurate to describe high frequency superconducting transformers with existing models.…”

Section: Introductionmentioning

confidence: 99%

Experimental and numerical study of high frequency superconducting air-core transformer

Liu

Wang

et al. 2021

Although many researches on superconducting air-core transformers have been carried out, it is mainly on the power frequency situation. The high-frequency characteristics of superconducting air-core transformers are still unclear. In this paper, we applied experimental and finite element simulation approach to study the operation and loss characteristics of high frequency superconducting air-core transformer made by YBa2Cu3O7−δ (YBCO) tapes. The numerical model established is based on the H formula and the E–J power law, and the edge degradation and anisotropy of the critical current density of the tape are considered in the model. The results show that the operating characteristics of superconducting transformers are significantly different from those of conventional transformers, and their operating characteristics have strong frequency and power dependence. The obtained findings can provide a theoretical basis for the design of high-frequency resonant transformers.