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전류분포가 3본-도체의 임계전류/교류손실 특성에 미치는 영향
류경우,최병주 한국전기전자재료학회 2003 전기전자재료학회논문지 Vol.16 No.5
AC loss is an important issue in the design of high-T$\sub$c/ superconducting power cables which consist of a number of Bi-2223 tapes wound on a former. In the cables, the tapes have different critical currents intrinsically. And they are electrically connected to each other and current leads. These make loss measurements considerably complex, especially for short samples of laboratory size. So special cautions are required in the positioning of voltage leads for measuring the true loss voltage. In this work we have prepared a conductor composed of three Bi-2223 tapes with different critical currents. The critical current and AC loss characteristics in the conductor have experimentally investigated. The results show that for uniform current distributions the conductor's critical current is proportional to the critical current of the Bi-2223 tape to which a voltage lead is attached. However it depends on the current non-uniformity parameter in the conductor rather than the tape's critical currents for nonuniform current distributions. The loss tests indicate that the AC loss is dependent on arrangements of voltage leads but not on their contact positions. The measured losses in the conductor also agree well with the sum of the transport losses measured in each Bi-2223 tape.
임성우,최용선,황시돌,한병성 한국초전도학회 2003 Progress in superconductivity Vol.4 No.2
Voltage-current characteristics of High Temperature Superconductor(HTS) tapes after applying the current beyond their critical current was investigated. When over-current is applied, the current begins to flow through the metal sheath instead of superconductor. The HTS tapes quenched were analyzed using V-I curve with various magnitudes of current. Two kinds of tapes were compared with each other to examine the influence of critical current on quench development. As a result, it was found that the resistance of superconductors and joule heat due to the over-current affect current distribution in HTS tapes. Critical current of HTS tapes was considered as a main factor deciding over-current characteristics.
고온초전도 BSCCO 팬케이크 권선에 인가되는 자장과 임계전류의 산정
具明煥(Myunghwan Koo),姜明勳(Myunghun Kang),李喜俊(Heejoon Lee),車貴守(Gueesoo Cha) 대한전기학회 2008 전기학회논문지 Vol.57 No.11
Critical current of the superconducting machines is limited by the magnetic field. When the magnetic field is not uniform, it is difficult to estimate the magnetic field and the critical current. This paper proposed a method for the estimation of tile magnetic field and the critical current of the HTS pancake windings which can be used to generate the high field magnet. A parameter which was needed to calculate the critical current of a BSCCO magnet with 10 pancake windings was obtained by tile experiment. Test which was carried out by using single pancake winding and magnet consisting of 10 pancake windings shows the proposed method can be an effective method for the estimation of the critical current of pancake windings.
“Leak Current” correction for critical current measurement of no-insulation HTS coil
송중빈,한승용 한국초전도.저온공학회 2017 한국초전도저온공학회논문지 Vol.19 No.2
Discrepancy between a power supply current and an actual “spiral” coil current makes the conventional 4-probe measurement ofa critical current (Ic) of a no-insulation (NI) high temperature superconductor (HTS) coil inaccurate and time-consuming. Thispaper presents a fast and accurate approach for Ic measurement of NI HTS coils. With an NI HTS coil energized at a constantramping rate, a complete analytic expression for the spiral coil current was obtained from a first-order partial differential equationthat derived from an equivalent circuit model of the NI coil. From the analytic solution, both spiral coil current and radial leakcurrent can be obtained simultaneously, which enables fast and accurate measurement of the NI coil Ic. To verify the proposedapproach, an NI double-pancake (DP) coil, wound with GdBCO tapes of 6 mm × 0.1 mm, was constructed and its Ic was repeatedlymeasured with various ramping rates in a bath of liquid nitrogen at 77 K. The measured results agreed well with the calculated ones,which validates the proposed approach to measure Ic of an NI HTS coil.
"Leak Current" correction for critical current measurement of no-insulation HTS coil
Song, Jung-Bin,Hahn, Seungyong The Korea Institute of Applied Superconductivity a 2017 한국초전도저온공학회논문지 Vol.19 No.2
Discrepancy between a power supply current and an actual "spiral" coil current makes the conventional 4-probe measurement of a critical current ($I_c$) of a no-insulation (NI) high temperature superconductor (HTS) coil inaccurate and time-consuming. This paper presents a fast and accurate approach for $I_c$ measurement of NI HTS coils. With an NI HTS coil energized at a constant ramping rate, a complete analytic expression for the spiral coil current was obtained from a first-order partial differential equation that derived from an equivalent circuit model of the NI coil. From the analytic solution, both spiral coil current and radial leak current can be obtained simultaneously, which enables fast and accurate measurement of the NI coil $I_c$. To verify the proposed approach, an NI double-pancake (DP) coil, wound with GdBCO tapes of $6mm{\times}0.1mm$, was constructed and its $I_c$ was repeatedly measured with various ramping rates in a bath of liquid nitrogen at 77 K. The measured results agreed well with the calculated ones, which validates the proposed approach to measure $I_c$ of an NI HTS coil.
Critical Performance Analysis of HTS Magnet Wires Using an Induced Current-Based Measurement System
Go, B. S.,Kim, K.,Jeong, S. H.,Lee, H.,Park, M.,Yu, I. K. Institute of Electrical and Electronics Engineers 2016 IEEE transactions on applied superconductivity Vol.26 No.4
<P>Studies on wide and stacked high-temperature superconducting (HTS) wires aim to increase the critical current of the wires. This paper describes the design and fabrication of an induced current-based performance measurement system and a critical performance analysis of HTS magnet wires using this system. In the experiment, the induced current, critical current, and joint resistance of stacked HTS wires under charge and discharge conditions were investigated. The results obtained were compared with those achieved using the four-terminal method, which is the conventional measurement method. The measurement system and the results of the critical performance analysis of the HTS wire are discussed in detail.</P>
Critical currents across grain boundaries in YBCO : The role of grain boundary structure
Miller Dean J.,Gray Kenneth E.,Field Michael B.,Kim, Dong-Ho The Korean Superconductivity Society 1999 Progress in superconductivity Vol.1 No.1
Measurements across single grain boundaries in YBCO thin films and bulk bicrystals have been used to demonstrate the influence of grain boundary structure on the critical current carried across the grain boundary. In particular, we show that one role of grain boundary structure is to change the degree of pinning along the boundary, thereby influencing the critical current. This effect can be used to explain the large difference in critical current density across grain boundaries in thin films compared to that for bulk bicrystal. These differences illustrate the distinction between the intrinsic mechanism of coupling across the grain boundary that determines the maximum possible critical current across a boundary and the measured critical current which is limited by dissipation due to the motion of vortices.
Estimation of the critical current of race-track HTS magnet considering angular dependency
Lee, Kyubong,Sim, Kideok,Lee, Changyoung,Kim, Seokho The Korea Institute of Applied Superconductivity a 2015 한국초전도저온공학회논문지 Vol.17 No.3
The high temperature superconducting (HTS) magnet has been developed for the high magnetic field applications such as NMR, MRI and other industrial machinery. In designing process of these HTS magnets, the accurate estimation on the critical current (Ic) is essential to predict and secure the electromagnetic performance. The critical current of 2G HTS tape has anisotropic Ic degradation characteristics with the application of magnetic field - angular dependency of critical current. It is known that the perpendicular magnetic field to the face of HTS tape makes dominant degradation on the critical current for conventional 2G HTS tape. However, recently developed 2G HTS tape has more complex characteristics due to the artificial pinning center. Therefore, the method for Ic estimation reflecting such characteristics of 2G HTS tape needs to be devised. The method considering the angular dependency is introduced in this paper. And the result of newly devised method is compared with that of previous method.
마용호,이주영,류경우,손송호,황시돌,Ma, Yong-Hu,Li, Zhu-Yong,Ryu, Kyung-Woo,Sohn, Song-Ho,Hwang, Si-Dol 한국전기전자재료학회 2007 전기전자재료학회논문지 Vol.20 No.7
The AC loss is an important issue in the design of the high temperature superconductor (HTS) power cables and fault current limiters. In these applications, a cylindrical HTS conductor is often used. In commercialization of these apparatuses, AC loss is a critical factor but not elucidated completely because of complexities in its measurement, e.g. non-uniform current distribution and phase difference between currents flowing in an individual HTS tape. We have prepared two cylindrical conductors composed of a Bi-2223 tape with different critical current density. In this paper, the AC loss characteristics of the conductors have been experimentally investigated and numerically analyzed. The result show that the measured losses for two conductors are not dependent on both arrangements and contact positions of a voltage lead. This implies that most of loss flux is only in the conductors. The loss for the Bi-2223 conductor with low critical current density is in good agreement with the calculated loss from Monoblock model, whereas the loss measured for the Bi-2223 conductor with high critical current density doesn't coincide with the loss calculated from the Monoblock model. The measured loss is also different from numerically calculated one based on the polygon model especially in low transport current.