Analytical approximations for the self-field distribution of a superconducting tape between iron cores

Iron-core electromagnets are used widely as applied-field switches in HTS flux pumps. It was recently reported that the critical current (I c) of the HTS wire is suppressed by up to 45% in the air-gap of the iron-core. Here, it is reported that the self-field I c of a single tape (unifilar) is suppressed from 357 A to 195 A while in the air-gap of the iron-core, agreeing closely with the previous study. This is extended by showing the I c response to perpendicular magnetic field is asymmetric, with peak I c of 249 A found to be at 0.16 T of applied field. This effect can be eliminated using an anti-parallel current configuration (bifilar), which is shown experimentally to recover close to the no-core self-field I c of 357 A with no observed asymmetry. The results of both types of switch configuration are closely replicated in finite-element modelling using COMSOL Multiphysics®. This is caused by the asymmetric interaction between the self-induced magnetic field of the HTS switch element and the magnetic circuit of the iron-core electromagnet.

Section: Resultssupporting

confidence: 78%

“…It has recently been reported that the self-field I c of an HTS wire in the air gap of an iron-core electromagnet is suppressed by almost 50% [27]. In this study, we build upon this work by empirically measuring the J c (B) characteristic of an HTS wire in the air gap of an iron-core electromagnet in liquid nitrogen (LN 2 ).…”

Section: Introductionmentioning

confidence: 97%

Critical current asymmetry in HTS switches using iron-core electromagnets

Rice¹,

Taylor²,

Moseley³

et al. 2022

“…However, during the magnetisation, the heat produced by PFM will hinder the realisation of the full trapped field and flux potential in CCs [40]. While zero field cooling and flux pumping have also been reported as general magnetisation methods for CCs [41][42][43][44][45][46], they have not been employed extensively in superconducting machines.…”

Section: Introductionmentioning

confidence: 99%

Magnetisation and demagnetisation of trapped field stacks in a superconducting machine for electric aircraft

Wang,

Zhang,

Hao

et al. 2023

Self Cite

This research presents a comprehensive and innovative approach to investigating the magnetisation and cross-field demagnetisation behaviour of high-temperature superconducting (HTS) coated conductors (CCs) in practical superconducting machines. This study introduces several novel contributions, including the operation of the machine in propulsion energy conversion mode, the exploration of harmonics interaction in a real electric machine environment involving CCs, and the extraction of these harmonics as cross-field components. A 2D electromagnetic-thermal coupled numerical model employing the finite element method (FEM) has been developed and validated against experimental data to simulate a partially superconducting machine. Upon magnetisation, the HTS stacks effectively operate as trapped field magnets (TFMs), generating rotor fields for motor operation. With a peak magnetic flux density of 462 mT of the trapped field stacks (TFSs) in the air gap, the average values of the fundamental and fifth harmonics of the tangential magnetic flux density experienced by the TFSs were observed to be 25 mT and 1.75 mT, respectively. The research has thoroughly examined the impact of cross-field demagnetisation parameters including amplitude and frequency on the demagnetisation of TFSs. Furthermore, the study has also investigated the magnetisation losses occurring in various layers of HTS tapes, encompassing the HTS layer, magnetic substrate layer, and silver stabiliser at different amplitudes and frequencies. Two tape structures, namely a semi-homogenised model and a multi-layered model, have been analysed in terms of magnetisation loss. Additionally, insights into the shielding effect and skin effect at high frequencies were obtained, offering valuable information on the performance of HTS TFSs exposed to high frequency scenarios, especially in high-speed machines for electric aircraft. The research outcomes are anticipated to provide valuable knowledge for the design and optimisation of HTS rotors employing TFSs in superconducting machines, contributing to the advancement of superconducting machine technology.

“…A number of these HTS switches and FPs have the configuration of placing a HTS wire in a narrow airgap of a C-shaped iron-core magnet [2,7,12,35]. However, the selffield critical current of the single CC within the iron-core air gap is suppressed by approximately 45%, which directly influences the switching performance and efficiency [7,12,40]. On the other hand, a bifilar stack of two antiparallel REBCO CCs was used as the switching element, which is preferable for gapped-iron-core-based HTS PCSs and HTS FPs.…”

Section: Introductionmentioning

confidence: 99%

“…On the other hand, a bifilar stack of two antiparallel REBCO CCs was used as the switching element, which is preferable for gapped-iron-core-based HTS PCSs and HTS FPs. Such a 'noninductive' structure of bifilar stacks effectively minimizes the self-induction of the switch and substantially increases the self-field critical current of the CC, which provides more stable load fields and significantly improves the efficiency of HTS switches and FPs [1,7,12,40].…”

Section: Introductionmentioning

confidence: 99%

Dynamic resistance and voltage response of a REBCO bifilar stack under perpendicular DC-biased AC magnetic fields

Sun

Geng

Badcock

et al. 2023

Dynamic resistance of REBCO coated conductors (CCs) is a key parameter in many high-temperature superconductor applications where CCs carry DC currents exposed to AC and DC magnetic fields, such as field-triggered persistent current switches, flux pumps, and fault current limiters. In this work, dynamic resistance and dynamic voltage has been studied via experiments and FEM simulations in a REBCO bifilar stack at 77 K under combined AC and DC magnetic fields with different magnitudes, frequencies, and waveforms. Our results show some distinct features of dynamic resistance and voltage from those under pure AC magnetic fields. With increasing DC magnetic fields, dynamic resistance exhibits an obvious linearity with applied AC magnetic fields, and becomes less dependent on the AC field frequency. The fundamental frequency of the dynamic voltage under DC magnetic fields becomes the same with that of the applied AC fields, which completely differs from the pure AC field case where the fundamental frequency doubles. For the first time, instantaneous threshold field (Bth) values are obtained from the dynamic voltage, which are substantically different in the field-increasing and field-decreasing process. These key differences are attributed to the dominant role of DC magnetic fields in determining the critical current of the superconductor, which significantly dwarfs the influence of AC fields. These new discoveries may help researchers better understand the electromagnetism of the superconductor and be useful for relevant applications.