• Journal of Power Electronics
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• v.19 no.1
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• pp.211-219
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• 2019

In magnetically coupled resonant (MCR) wireless power transfer (WPT) systems, the introduction of additional intermediate coils is an effective means of improving transmission characteristics, including output power and transmission efficiency, when the transmission distance is increased. However, the position of intermediate coils in practice influences system performance significantly. In this research, a three-coil MCR WPT system is adopted as an exemplification for determining how the spatial position of coils affects transmission characteristics. With use of the fundamental harmonic analysis method, an equivalent circuit model of the system is built to reveal the relationship between the output power, the transmission efficiency, and the spatial scales, including the axial, lateral, and angular misalignments of the intermediate and receiving coils. Three cases of transmission characteristics versus different spatial scales are evaluated. Results indicate that the system can achieve relatively stable transmission characteristics with deliberate adjustments in the position of the intermediate and receiving coils. A prototype of the three-coil MCR WPT system is built and analyzed, and the experimental results are consistent with those of the theoretical analysis.

• Progress in Superconductivity and Cryogenics
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• v.10 no.1
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• pp.42-47
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• 2008

In this paper, the fault current limiting characteristics for the superconducting fault current limiter(SFCL) using magnetic coupling between two coils were investigated. The SFCL consists of a high-$T_c$ superconducting(HTSC) element and two coils. This SFCL has different characteristics that depend on the connection form, the winding direction and the inductance ratio of two coils. The impedance and the operational current of the SFCL can be adjusted higher or lower than the resistance and the critical current of HTSC element. Therefore, the SFCL can change the amplitude of the limited fault current. To confirm it, the HTSC element was modeled and the fault current limiting characteristics of the SFCL were analysed through computer simulation. It was obtained from the analysis that the connection form and the winding direction of two coils of the SFCL were the important design parameters.

• Progress in Superconductivity and Cryogenics
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• v.9 no.2
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• pp.7-10
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• 2007

Persistent mode HTS pancake coil has been fabricated using a coated conductor by a "wind-and-flip" method. A coated conductor with the length of 1.2 meters was divided at the center along the length. The sliced coated conductor was wound on a pair of bobbins with a diameter of around 4 cm and two pancake coils connected superconductively without a resistive joint were prepared. By flipping one of the pancake coils, the magnetic field generated by each coil is to be aligned to the same direction and generate meaningful magnetic field while the magnetic fields of two spit coils are canceled without flipping. Permanent current was induced by flowing current to the coil immersed in liquid nitrogen pool using a power supply. A magnetic field of 48.8 Gauss was generated when 20 A of current was flowing in the pancake coils. The "Wind and flip" method can be applied for the fabrication of a long solenoid magnet by winding a sliced coated conductor on a cylindrical bobbin. It is also introduced that the construction of multiple sets of pancake (or solenoid) coils is possible by a "wind-and-flip" method using a wide coated conductor.

• Progress in Superconductivity and Cryogenics
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• v.9 no.3
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• pp.13-15
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• 2007

We employed home-made position marking module in the scanning Hall probe system. The module is composed of two coils of which gap, a, between wires in a coil is $500{\mu}m$. We appiled 10-35mA of current with 15Hz in the coils and recorded ac corresponding magnetic field signal with respect to measuring time while we measured DC field profiles produced due to superconducting film in a perpendicular magnetic field. We calibrate the position, x, of coils using the measuring time and location of the coils in the holder. The error range was about ${\pm}0.1mm$. We test the module as we applied current of 100A and filed of 1kG in the superconducting tape. It was confirmed that there was no interference between superconducting tape and marking coils.

• Progress in Superconductivity and Cryogenics
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• v.1 no.2
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• pp.43-48
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• 1999

The normal zone propagation (NZP) velocity and V-I characteristics of two Bi-2223 pancake coils with different Ag/SC ratio were investigated based on the experimental results and broad resistive transition were obesved in two coils. The measured NZP velocity of coil was found to be faster due to increase of Ag/SC ratio, and agree well with calculated data from two dimensional heat balance equation.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 1999.02a
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• pp.109-112
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• 1999

The normal zone propagation (NZP) velocity and V-I characteristics of two Bi-2223 pancake coils with different Ag/SC ratio were investigated by experiment. Non-uniformity of Ic and broad restive transition was oberserbed in two coils. The NZP velocity of azimuth direction is faster than radius direction, and the NZP velocity of coil with higher Ag/SC ratio is faster than another coil with lower Ag/SC ratio.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 1999.02a
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• pp.61-64
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• 1999

Dry winding is generally adopted in superconducting coils of an UPS system. In these kinds of coils a quench is often initiated by a disturbance such as wire motion that generates a highly localized normal zone in a superconducting wire. To fabricate the stable coils, stability of the superconducting wire should be touched. In this paper, a model for a transient stability analysis of the wire is suggested. The influence of a local disturbance, cooling, an external field and a stabilizer to superconductor ratio on the wire stability is investigated and discussed.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2000.02a
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• pp.119-120
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• 2000

The thermal shield for the TF coils and PF coils has been located between the coils and vacuum vessel. The thermal shielding cryopanel is cooled under 80K by a fored flow of helium gas using cooing pipes on the cryopanel. Design of the KSTAR thermal shield of vacuum vessel is described.

• Proceedings of the KIEE Conference
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• 1994.11a
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• pp.120-123
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• 1994

The purpose of this paper is to describe the mutual inductance between two non-coaxial circular coils in coil gun. As being in many electromagnetic applications, one of them is fixed and the other one is moving and, being not supported, its axis may not coincide with the axis of the fixed coil. This paper presents a method for the calculation of the mutual inductance in case of non-coaxial coupled coils, the characteristics of this inductance and experimental results. For the computation, the complete elliptic integrals formula and mesh matrix technique were introduced. This method enables accurate results from relatively simple procedure and calculation program.

• Proceedings of the KIEE Conference
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• 1996.07a
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• pp.95-97
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• 1996

Circular coils are widely used in electromagnetic applications, and the force in a sets of coils consisting of more than two can be divided into three components. Among them, one component called radial force is acting on the radial axis, and it is exposed as stree or impact. Calculation of the radial force was used to be performed by introducing Ampear's law of force which is $F=J{\times}B$. However, many cases in analyzing a system, calculation method from the mutual inductance between the coils is oftenly employed to get the axial force and resulting dynamics. In this case, if the calculation of radial force from the mutual inductance is possible, flow of the calculation for the system analysis would be much more simpler.