An effective way to reduce AC loss of second-generation high temperature superconductors

Wang, Mingyang; Zhang, Min; Song, Meng; Li, Zhuyong; Dong, Fangliang; Hong, Zhiyong; Jin, Zhijian

doi:10.1088/1361-6668/aaee05

Cited by 27 publications

(12 citation statements)

References 32 publications

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“…The results have demonstrated that the critical current is not debased for striation width over 150 µm, and the AC loss can be decreased effectively. Different from conventional filamentary HTS CCs, a soldered-stacked-square (3S) wire has been proposed in [216]. The fundamental manufacturing process is to divide HTS CCs into 1-mm-wide ones, solder with a soldering furnace, and put them into a stack, as shown in Figure 15.…”

Section: Ac Loss Reduction Techniques 61 Filamentation Of Hts Ccsmentioning

confidence: 99%

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Alternating Current Loss of Superconductors Applied to Superconducting Electrical Machines

Zhang¹,

Wen²,

Grilli

et al. 2021

Energies

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Superconductor technology has recently attracted increasing attention in power-generation- and electrical-propulsion-related domains, as it provides a solution to the limited power density seen by the core component, electrical machines. Superconducting machines, characterized by both high power density and high efficiency, can effectively reduce the size and mass compared to conventional machine designs. This opens the way to large-scale purely electrical applications, e.g., all-electrical aircrafts. The alternating current (AC) loss of superconductors caused by time-varying transport currents or magnetic fields (or both) has impaired the efficiency and reliability of superconducting machines, bringing severe challenges to the cryogenic systems, too. Although much research has been conducted in terms of the qualitative and quantitative analysis of AC loss and its reduction methods, AC loss remains a crucial problem for the design of highly efficient superconducting machines, especially for those operating at high speeds for future aviation. Given that a critical review on the research advancement regarding the AC loss of superconductors has not been reported during the last dozen years, especially combined with electrical machines, this paper aims to clarify its research status and provide a useful reference for researchers working on superconducting machines. The adopted superconducting materials, analytical formulae, modelling methods, measurement approaches, as well as reduction techniques for AC loss of low-temperature superconductors (LTSs) and high-temperature superconductors (HTSs) in both low- and high-frequency fields have been systematically analyzed and summarized. Based on the authors’ previous research on the AC loss characteristics of HTS coated conductors (CCs), stacks, and coils at high frequencies, the challenges for the existing AC loss quantification methods have been elucidated, and multiple suggestions with respect to the AC loss reduction in superconducting machines have been put forward. This article systematically reviews the qualitative and quantitative analysis methods of AC loss as well as its reduction techniques in superconductors applied to electrical machines for the first time. It is believed to help deepen the understanding of AC loss and deliver a helpful guideline for the future development of superconducting machines and applied superconductivity.

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Section: Ac Loss Reduction Techniques 61 Filamentation Of Hts Ccsmentioning

confidence: 99%

“…The fundamental manufacturing process is to divide HTS CCs into 1-mm-wide ones, solder with a soldering furnace, and put them into a stack, as shown in Figure 15. In [216], the authors reported that the 3S concept can help to decrease AC loss by 80% compared with originally uncut tapes.…”

Section: Ac Loss Reduction Techniques 61 Filamentation Of Hts Ccsmentioning

confidence: 99%

Alternating Current Loss of Superconductors Applied to Superconducting Electrical Machines

Zhang¹,

Wen²,

Grilli

et al. 2021

Energies

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“…Basic mechanical and transport characteristics of the REBCO conductor after narrowed and stacked have been studied in our previous work [19][20][21]. Specially, when the bending diameter is larger than 60 mm, the critical current of the stacked REBCO conductor will not be reduced.…”

Section: Fabrication Of Ns Wire and Coilmentioning

confidence: 99%

A novel REBCO conductor design to reduce screening-current field in REBCO magnets

Wang

Yan

et al. 2019

Phys. Scr.

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Due to its very high critical fields, the second-generation high-temperature superconductor (2 G HTS) has been, and is being, used in high-field magnets. However, a persistent screening current induced in the REBCO conductor under time-varying conditions distorts the magnetic field, spatially and temporally. We describe a novel REBCO conductor design composed of narrow-stacked (NS) wire, a bundle of 1 mm wide REBCO tapes. The design is based on a fundamental notion that the narrower the REBCO tape width, the smaller the screen-current field (SCF). In this paper, both experimental and simulation work were carried out to analyze SCF in a REBCO coil wound with an NS wire. We demonstrate that the critical current of NS wires can be consistent with the conventional REBCO tape to meet the application requirements. Meanwhile, NS wire indeed substantially results in small SCF, an important requirement in high-field magnets such as for NMR, MRI, and HEP that may rely on REBCO conductor.

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“…The theories of magnetization loss in thin superconducting strips developed by Brandt et al [108] and Zeldov et al [142] indicate that the magnetization loss is proportional to the HTS tapes' width at the same Ic. Therefore, an effectively method to reduce AC loss in REBCO conductor is cutting a single tape into multi narrow filaments [25]- [27].…”

Section: Striated Wiresmentioning

confidence: 99%

“…In a striated REBCO wire, the superconducting layer is striated into separated narrow filaments. As a consequence, the magnetization loss can be significantly reduced due to the decreased size of the induced current loops [25]- [27]. A Roebel REBCO cable consists of several conductor strands.…”

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confidence: 99%

AC Loss Reduction in HTS Coils and Armature Windings of Fully Superconducting Motors

You¹

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High AC loss in armature windings is one of the greatest barriers to achieve practical fully-HTS (high-temperature superconducting) motors. At present, AC loss estimation for HTS armature windings is one of the core technical challenges. AC loss behaviours and AC loss reduction methodologies have not been fully investigated in REBCO (REBa2Cu3O7-x, RE: rare earth) HTS armature windings carrying AC current under rotating magnetic fields. Many open questions need to be studied, of which this thesis addresses the three most prominent: can significant AC loss reduction be achieved by using low-loss MFDs (magnetic flux diverters); is it feasible to apply MFD structure to the HTS armature windings; and what kind of REBCO conductor types for armature windings generate less AC loss. The goal of this thesis is applying experimental and numerical methods to investigate AC loss behaviours and AC loss reduction methodologies in the HTS windings wound with REBCO wires. Specifically, it includes investigating AC loss reduction in HTS coil assembly by using low-loss MFDs; building numerical models for fully-HTS motors; and developing methodologies to achieve AC loss reduction in the HTS armature windings. We firstly explored the effectiveness of AC loss reduction on a REBCO four double-pancake coil assembly by using low-loss MFDs, MPP (Molypermalloy powder) MFDs and HF (High flux) MFDs. These have not been studied with HTS coils before. The measured and simulated results show that both MFDs can significantly reduce the total loss (the summation of the losses in the HTS windings and MFDs) in the system. At 77 K and 40 A coil current, compared with the coil assembly without MFDs, the total loss with HF and MPP MFDs is reduced by 77% and 81%, respectively. Although MPP MFDs show slightly better performance in reducing total loss at low coil current, HF MFDs are the more obvious option for AC loss reduction in high magnetic field applications owing to their relatively high saturation field. Next, we developed numerical models to investigate the AC loss reduction in the armature windings of a 50 kW fully HTS motor by applying pole shoes, which function as MFDs. For comparison, two motor designs with and without pole shoes have been considered in the finite-element method (FEM) models. REBCO coated conductors were considered for both the armature and field windings, and 2D FEM models of both designs were built using the T-A formulation (T: current vector potential, A: magnetic vector potential) and rotating meshes. The simulation results show that flux diverting pole shoes reduced the perpendicular magnetic field in the armature windings and provided a 51% AC loss reduction, without weight penalty or motor power rating reduction. Finally, AC loss simulation in HTS armature windings of a 100 kW HTS motor wound with different types of REBCO conductor arrangements were carried out. Three types of conductors, 4 mm-wide REBCO conductors, 14/2 (14 strands, each strand is 2 mm wide) REBCO Roebel cables and striated REBCO conductors with four 1 mm-wide filaments, were considered in the armature windings. The simulation results show that both Roebel cables or striated conductors can significantly reduce the AC loss in the armature windings compared with 4 mm-wide conductors. Further, a 2% AC loss reduction can be achieved in the armature winding wound with REBCO conductors with asymmetric Ic(B, θ) characteristics by simply flipping the direction of the conductors. This work provides a method to achieve large AC loss reduction in HTS coil windings by using low-loss MFDs. Also, it supplies practical implications for designing armature windings of fully-HTS superconducting rotating machines. The methodologies of AC loss reduction in this thesis also can be applied to other HTS applications, such as transformers, and fast ramping magnets.

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An effective way to reduce AC loss of second-generation high temperature superconductors

Cited by 27 publications

References 32 publications

Alternating Current Loss of Superconductors Applied to Superconducting Electrical Machines

Alternating Current Loss of Superconductors Applied to Superconducting Electrical Machines

A novel REBCO conductor design to reduce screening-current field in REBCO magnets

AC Loss Reduction in HTS Coils and Armature Windings of Fully Superconducting Motors

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