Transport AC losses analysis of twisted quasi-isotropic conductor

https://doi.org/10.1016/j.physc.2020.1353707Get rights and content

Highlights

  • AC losses of twisted quasi-isotropic conductor were measured, calculated and analyzed.

  • 3D simulation based on the T-A formulation was adopted.

  • Minimum twisted pitch length of the quasi-isotropic conductor was obtained.

  • Reduction of transport AC loss of the quasi-isotropic conductor was discussed.

Abstract

The second-generation (2 G) high temperature superconducting (HTS) conductor is widely used in high-field magnets and power transmission cables and its AC loss is one of the main obstacles. This paper mainly analyzed AC losses of twisted quasi-isotropic conductor stacked by 2 G HTS tapes and copper tapes by simulation and experimental methods at 77 K. A twisting apparatus was designed and manufactured for fixing and twisting the quasi-isotropic conductor accurately and the transport AC losses of the conductor with different twisted angle were measured by four-probe method under different frequencies. Meanwhile, a 3D simulation based on the T-A formulation was adopted to handle simulation challenges of HTS tapes with high aspect ratio and overall understand AC losses on the twisted quasi-isotropic conductor. Simulation results are in good agreement with the measured ones and the current distribution in the HTS tapes was investigated in detail. The results are helpful for fully understanding transport AC losses characteristics of twisted quasi-isotropic conductor.

Introduction

wning to the characteristics of high current capacity with low AC loss, mechanical flexibility and anti-electromagnetic interference, the second-generation (2 G) high temperature superconducting (HTS) conductor has become a promising choice for commercial application [1,2]. In order to improve the current carrying capacity and weaken the magnetic anisotropy of HTS conductor, a quasi-isotropic HTS conductor structure was proposed by North China Electric Power University (NCEPU) [3], [4], [5]. It is well known that when 2 G HTS conductor transmitting alternating current (AC), AC loss will be generated in the superconducting layer and the metal layer, which includes the hysteresis loss (pH), coupling loss (Pc) and eddy current loss (Pe). The heat caused by AC loss will increase the difficulty for cooling, reduce the current carrying capacity and affect the stability of superconducting devices. AC loss of the quasi-isotropic conductor stacked by 2 G HTS tapes with large current capacity was well studied by using finite element method (FEM) based on 2D H formulation for its centrosymmetric structure and some related reports have already been available [6,7].

With the continuous research on twisted stacked-tape cable conductor (TSTC), it has been found that the twisting operation of HTS conductors can effectively improve their overall characteristics, especially in terms of reducing AC losses [8], [9], [10]. Therefore, to carry out some studies on the twisted quasi-isotropic superconducting conductor is essential nowadays. However, the twisted quasi-isotropic structure stacked by high aspect ratio of HTS tapes and copper tapes cannot be used for dimensional reduction, which resulting in huge number of mesh elements and intensive heavy computation burden by using H formulation.

In this paper, an efficient 3D simulation based on the T-A formulation will be adopted to estimate the current distribution over the twisted HTS tapes and AC loss over the entire conductor. At the same time, the transport AC loss of the quasi-isotropic conductor with different twisted angles will be measured by four-probe method under various frequencies in liquid nitrogen (LN2) bath. In order to fix the conductor and change the twist angel, a twisting apparatus will be designed and fabricated. The critical current of the conductor with different twist angles will be measured as well.

Section snippets

Configuration of the quasi-isotropic superconducting conductor

The three-dimensional and cross-section view of the quasi-isotropic conductor is presented in Fig. 1(a), which has a square shape consists of 4 units and is banded with sticky aluminum foil. Copper and HTS tapes with the same width of 2 mm are stacked alternatively. The HTS tapes used in this paper are fabricated by Shanghai Superconductor Technology Co. Ltd., with 1 µm superconducting layer and the thickness of copper tape is about 200 µm. A 300 mm long quasi-isotropic conductor was prepared

Results and discussion

While the quasi-isotropic conductor transports alternative current, coupling loss tends to generate when the magnetic field parallel to the tape. It is known that the induced current and the time constant of the coupling current are both proportional to the square of the twist pitch length of a twisted stacked-tape cable [18]. Therefore, in terms of the twisted quasi-isotropic conductor, it is desirable to minimize the coupling losses by reducing the twist pitch length. However, based on the

Conclusion

In this paper, transport AC losses of twisted quasi-isotropic conductor were analyzed by 3D T-A formulation and experiment. At 5% degradation of the critical current, the minimum twisted pitch length was measured. Transport AC losses at several twist angles were measured and calculated under different frequencies and the results are in good agreement. Transport AC loss can be reduced to be 79% by decreasing twist pitch length. Compared with non-twisted quasi-isotropic conductor, the twisted one

CRediT authorship contribution statement

Wei Pi: Writing - review & editing, Supervision, Funding acquisition. Yiran Meng: Investigation, Writing - original draft. Tie Guo: Formal analysis. Defu Wei: Resources. Yueyin Wang: Software, Visualization. Ziqiu Liu: Validation. Guoqing Li: Data curation. Yinshun Wang: Methodology, Project administration.

Declaration of Competing Interest

None.

Acknowledgements

This work was supported in part by State Grid under Grant DG71–19–004 and the National Natural Science Foundation of China under Grant 51877083.

References (25)

  • Zhuyong Li

    Evaluation of Electrical and Mechanical Characteristics for a Twisted Soldered-Stacked-Square (3S) HTS Wire With 1 mm Width

    IEEE Trans. Appl. Supercond.

    (Apr. 2018)
  • Zhuyong Li

    A Study on Critical Current and AC Loss Characteristics of Novel 2G HTS Narrow Wires

    IEEE Trans. Appl. Supercond.

    (Jun. 2016)
  • Cited by (10)

    • Persistent current effects in highly homogeneous superconducting magnets

      2022, Physica C: Superconductivity and its Applications
      Citation Excerpt :

      The homogeneity of the magnetic field directly affects the imaging quality, nucleus mass measurement accuracy, etc [1,2]. When a superconducting magnet operates, it generates various induced currents, which affect the quality of the magnetic field in various ways [3,4]. The eddy current and coupling current both decay rapidly, while the persistent current, which flows inside the superconducting filament and forms a loop, remains for a long time after the magnetic field is stabilized and has a large impact on the magnetic field quality [5–7].

    • Effects of twisting pitch on critical current of HTS tapes in Quasi-isotropic strand

      2021, Physica C: Superconductivity and its Applications
      Citation Excerpt :

      A quasi-isotropic conductor with high engineering current density is further proposed [9,10]. High current-carrying conductor connected in parallel by multiple tapes generates AC loss, non-uniform current distribution and thermal instability if transmitting AC current or in excitation [11], transposition or twisting technique is an effective way to reduce AC loss and equalize current distribution. In previous research, only preliminary experimental measurements were made on the critical twist pitch of the Q-IS [12,13], but the research of tapes in Q-IS did not consider their position characteristics.

    View all citing articles on Scopus
    View full text