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Optimum Reduction of Self Field Effects in a Bi-2223 Stacked Super Conducting Bus Bar
Nah,Wansoo,Kang,Hyoungku,Park,Ii-Han,Joo,Jinho,Oh,Sang-Soo,Ryu,Kang-Sik,Yoo,Jaimoo 성균관대학교 1998 학술회의지원논문목록집 Vol.1998 No.-
High Tc Superconductors. such as Bi-2223, have been promising candidates far an eleclrical bus bar because bus bar has relatively low self magnetic field. It has been found that the critical current of Bi-2223 stacked tapes is much less than the total summation of critical currents of each tape, which in mainly attributed to the self magnetic fields. Furthemore, since the critical current degradation of Bi-2223 tape is greater in the normal magnetic field (to the tape surface) than in the parallel one, detailed magnetic field configuration are required to reduce the self field effects. Conceptually by rearranging each stacked tape properly, the self field effects could be minimized In this paper, we calculate the self field effects of stacked conductor defining self field factors of normal and parallel magnetic fields to the tape surface. And we propose an optimum shape of octagonal structured bus bar which has minimum self field effects.
Analytic Approaches to Quench Behaviours of Superconducting Transformer
Nah,Wansoo,Joo,Jinho,Cha, Guee Soo 성균관대학교 1997 학술회의지원논문목록집 Vol.1997 No.-
This paper describes the quenches in superconducting transformer. Magnetizing current effecfs have been considered for the maximum temperature rise estimation during quenches. By introducing the first order model of the infinite solenoid, we calculated the mutual and Ieskage inductances of the coaxial-wound-superconducting transformers. As the permeability of the ttansformer core goes up the leakage inductances of the transformer goes down. These varying permeability effects could be explained through the suggested models. In this paper, the analytical results on the maximum temperature rise estimation, taking account of the magnetizing current, are presented.
Self Field Effect Analysis of Bi-2223 Tape-Stacked-Cable With Constant Current Density Assumption
Nah, Wansoo,Joo, Jinnho The Korean Institute of Electrical and Electronic 2000 Transactions on Electrical and Electronic Material Vol.1 No.1
In this paper, we analyze self field effects of Bi-2223 tape-stacked cable assuming constant current density in the cross section of stacked cable. Generally, the critical current of Bi-2223 tape-stacked-cable in much less than the total summation of critical currents of each tape, which is mainly due to the self magnetic fields of the cable itself. Therefore, to predict the critical current of Bi-2223 tape-stacked-cable, we needs to analyze the self filed effects on the stacked cable as well as critical current density data(J$\_$C/) of one tape. To make it more complex, the critical current degradation of Bi-2223 tape is an-isotropic; the critical current is lower in the normal magnetic field(to the tape surface) than in the parallel field. In the paper, a novel approach to predict the critical current of a Bi-2223 tape-stacked-cable from a J$\_$C/-B curve of one tape is presented with the assumption of constant current density across the stacked cable, The approach basically includes the load analysis of the stacked tapes, and its usefulness is confirmed by the experimental data.
永久電流 모드를 가지는 超傳導 MRI 마그네트의 勵磁에 대한 硏究
나완수 成均館大學校 科學技術硏究所 1996 論文集 Vol.47 No.1
Superconducting MRI(Magnetic Resonance Image) magnets have various shim coils for the uniform magnetic field, operating in persistent-current-mode. The shim coils, especially between the Z^2 shim and main coils, are magnetically strongly-coupled such as transformer, which disturbs the magnetic uniformities during energization. Since the resistances of the coils are absolutely zero (at DC current) in the superconducting state, the final target currents get contaminated by the magnetically-coupled--shim-coil energization. In this paper, the energization circuits for superconducitng MRI manget are analyzed and the effective way of energizations are proposed. Finally, distributions of magnetic fields after energizations are reported.
나완수 成均館大學校 科學技術硏究所 1996 論文集 Vol.47 No.2
Superconducting transformers are superior to conventional ones in many respects, such as in high efficiency, light weight, and low life-cycle cost. These advatages mainly come from high current density in supercondcuting windings. But, due to high resistivity of matrix around superconductors, this high current density could lead to high density of heat when quench occurrs in superconducting windings. Of course, quench protection scheme should be included in superconducting transformer system, but. the situation is different from DC superconducting magnet system, e.g. MRI magnet system, due to intrinsic AC operation of transformer. In this paper two essential quench protection schemes are studied and the protection principles are established for AC conditions. Finally a protection scheme without auxiliary windings is suggested, using derived equations in this paper.
Bi-2223 고온 초전도 코일의 영구전류 운전특성 실험
최세용,나완수,김정호,주진호,하홍수,오상수 성균관대학교 2003 학술회의지원논문목록집 Vol.2003 No.-
In this paper, we fabricated a persistent current mode magnet using Bi-2223 HTS tapes. The coil system consists of double pancake magnet and a persistent current switch and jointed them with solder. Persistent current mode operation of the system was measured experimentally by the decay behavior of the current. We found that resistive component of the system including flux flow resistance lead the exponentially field decay with time.
The AC Loss Estimation of Bi-2223/Ag Superconductor Tapes in Polygonal Configuration
Seyong Choi,Wansoo Nah IEEE 2010 IEEE transactions on applied superconductivity Vol.20 No.3
<P>In this paper, we have studied the electromagnetic phenomenon and AC losses of assembled high-T<SUB>c</SUB> superconductor (HTS) tapes using the finite element method (FEM) approach. The model cable is composed of several Bi-2223/Ag tapes with polygonal shape on the cylindrical former that was arranged in parallel along the conductor axis. The HTS tape usually shows complex material properties, which are described by the nonlinear resistivity and the anisotropy against the external magnetic flux density as well as its angle. The numerical calculation was carried out considering the field dependence of critical current density and index value, which accounts for the anisotropy of the Bi-2223/Ag tape. The calculated AC losses were compared with the experimental results and with the theoretical values. It was observed that the analytic formulae are not proper to predict the AC loss of the multi-stranded conductor that is presented here. The adjacent tape's effect of the conductor on the AC loss was also investigated and discussed.</P>