Experimental Analysis on Initial Current Decay Characteristics of Persistent-Mode HTS Coil by External Alternating Magnetic Field

Park, Young Gun; Lee, Chang Young; Lee, Jiho; Nam, Seokho; Chung, Yoon Do; Yoon, Yong Soo; Ko, Tae Kuk

doi:10.1109/tasc.2014.2373652

Cited by 25 publications

(16 citation statements)

References 10 publications

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“…This is distinct from dynamic resistance model under homogeneous ac field. The result may be indicative in designing superconducting motors 16 , especially in reducing persistent current decay in rotor stack tapes 17 or coils 18 which are under ripple traveling waves. After the transport current exceeds 200A, two phenomena in the V-I curves in Fig.…”

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confidence: 99%

Voltage-ampere characteristics of YBCO coated conductor under inhomogeneous oscillating magnetic field

Geng

Shen

et al. 2016

Applied Physics Letters

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Direct current carrying type II superconductors present a dynamic resistance when subjected to an oscillating magnetic field perpendicular to the current direction. If a superconductor is under a homogeneous field with high magnitude, the dynamic resistance value is nearly independent of transport current. Hoffmann and coworkers [C. Hoffmann, D. Pooke, and A. D. Caplin, IEEE Trans. Appl. Supercond. 21, 1628 (2011)] discovered, however, flux pumping effect when a superconducting tape is under an inhomogeneous field orthogonal to the tape surface generated by rotating magnets. Following their work, we report the whole Voltage-Ampere (V-I) curves of an YBCO coated conductor under permanent magnets rotating with different frequencies and directions. We discovered that the two curves under opposite rotating directions differ from each other constantly when the transport current is less than the critical current, whereas the difference gradually reduces after the transport current exceeds the critical value. We also find that for different field frequencies, the difference between the two curves decreases faster with lower field frequency. The result indicates that the transport loss is dependent on the relative direction of the transport current and field travelling, which is distinct from traditional dynamic resistance model. The work may be instructive for the design of superconducting motors. It is well known that type II superconductors carrying a direct current present a resistance when they are under a perpendicular oscillating magnetic field. 1-10 Theoretical analysis 1,3,7,8 and experimental results 1-7,10 have shown that this resistance is due to flux flow caused by the interaction between the transport current and the applied field, and it is defined as dynamic resistance. The dynamic resistance value is proportional to the applied field magnitude and frequency if the superconductor in a homogeneous field, and it is nearly independent of transport current if the field magnitude is high. 7 Hoffmann and coworkers 11 discovered flux pumping effect when a piece of superconducting stator connecting to a superconducting load was subjected to inhomogeneous magnetic fields orthogonal to the tape surface generated by rotating permanent magnets. Researchers from VUW 12 pointed out that dynamic resistance is the main limiting factor of saturation current in the flux pump. Concerning the open circuit voltage, they proposed a geometrical explanation considering screening current. 13 All these existing researches 11-13 focus on the flux pumping effect, where the superconducting stator generates dc power. In this letter, we extend the research to the V-I characteristics of YBCO Coated Conductor (CC) under rotating permanent magnets. The experimental system is shown in Fig. 1(a), which is similar to rotating magnets flux pumps 11-15. Eight Neodymium 52 magnets with a diameter of 20mm are uniformly mounted on a round copper disc. The outer diameter of the disc is about 81mm. All magnets were mounted with their north poles fa...

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confidence: 99%

Voltage-ampere characteristics of YBCO coated conductor under inhomogeneous oscillating magnetic field

Geng

Shen

et al. 2016

Applied Physics Letters

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“…However, for the motion condition, the HTS magnet will subject to a time-varying magnetic field. Compared with the isolated static condition, the current in the closed-loop circuit attenuates faster, and the current decay rate is relevant to the amplitude, frequency, and angle of the time-varying magnetic field [9,10]. That is, the current decay rate is more than related to the joint resistance and the index dissipation [9].…”

Section: Introductionmentioning

confidence: 99%

The Underlying Mechanism of Faster Current Attenuation of HTS Magnet in Persistent Current Mode Subject to the Traveling Magnetic Fields

Wang

Wang²,

Deng

et al. 2020

J Supercond Nov Magn

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High-temperature superconducting (HTS) magnet, due to its greater performance of magnetic field at higher temperature (20-40 K), better thermal stability, smaller volume and weight under the same requirements, and lower refrigeration costs, has attracted growing attention in the ultra-high-speed maglev system, high field magnet, and some other applications. Considering the practical requirements, closed-loop method is generally adopted in HTS magnet to maintain the persistent operation and to output the stable magnetic fields. But the accelerated current attenuation occurs when the HTS magnet is subjected to traveling magnetic fields, which is not conducive to the long-term operation. Therefore, this paper aims to investigate the essence of current attenuation of HTS magnet in persistent current mode under traveling magnetic fields and to further suppress this adverse behavior. In this study, to calculate the current distribution and dynamic resistance, a two-dimensional (2-D) finite element model (FEM) was established and verified by comparing with the experimental results. It can be seen from the simulation results that the dissipative losses caused by dynamic resistance present a non-negligible effect on the current attenuation of the magnet. And the mechanism of faster current attenuation was well explained by the variation of the dynamic resistance under the traveling magnetic fields.

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“…Therefore, it is necessary to study the characteristics of bulk HTSs exposed to an AMF. The current decay characteristics of an HTS coil operated in persistent current mode under AMF are widely studied [14][15][16], which could be instructive for reduction in current decay of HTS coils. The loss of suspension force of a bulk HTS in the AMF above a PM guide rail has been studied, and results showed that the decrease in the guiding force became more obvious with the increase in the amplitude of the magnetic field [17].…”

Section: Introductionmentioning

confidence: 99%

Experimental analysis on temperature characteristics of a rectangular bulk YBCO exposed to alternating magnetic field

et al. 2019

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The motion of magnetic flux will cause temperature rise inside of a bulk high-temperature superconductor (HTS) when exposed to an alternating magnetic field (AMF). In levitation system, like superconducting motors, bearing and vehicle, however, bulk HTSs are always subjected to ripple fields due to mechanical vibration, as well as harmonic field of armature windings, which will cause energy loss inside of bulk HTSs. Part of the heat caused by the energy loss is transferred to liquid nitrogen (LN 2) through the surface of bulk HTSs, and the other part will lead to temperature rise inside bulk HTSs. We experimentally analyzed the temperature characteristics of bulk YBCO under different AMF frequencies in this article. And the effect of AMF on the temperature rise of the bulk HTS under different cooling heights (CHs) and working heights (WHs) was also studied. The results showed that the higher the CH, the greater the temperature rises inside the bulk HTS. Besides, the temperature of the whole bulk HTS increases with the decrease in the WH and the increase in AMF frequency. The results and analyses of this article are useful for the application of bulk HTSs in the high-speed rotating and transportation systems.

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Experimental Analysis on Initial Current Decay Characteristics of Persistent-Mode HTS Coil by External Alternating Magnetic Field

Cited by 25 publications

References 10 publications

Voltage-ampere characteristics of YBCO coated conductor under inhomogeneous oscillating magnetic field

Voltage-ampere characteristics of YBCO coated conductor under inhomogeneous oscillating magnetic field

The Underlying Mechanism of Faster Current Attenuation of HTS Magnet in Persistent Current Mode Subject to the Traveling Magnetic Fields

Experimental analysis on temperature characteristics of a rectangular bulk YBCO exposed to alternating magnetic field

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