• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.5
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• pp.473-477
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• 2005

A Bi-2223 tape has been developed for power applications such as a fault current limiter, a power cable and a superconducting magnetic energy storage system. In such applications, the Bi-2223 tape carries time varying transport current and in addition experiences time varying external magnetic field. It is well known that the external magnetic field not only causes magnetization loss in the Bi-2223 tape, but also drastically increases transport loss due to a so-called 'dynamic resistance' We developed an evaluation setup, which can measure transport loss in external at magnetic fields. Using this equipment, we measured the dynamic resistances for various amplitudes and frequencies of an external at magnetic field perpendicular to the face in the tape. Simultaneously we investigated the effect of an external ac field on transport loss with different experimental conditions. This paper describes test results ana discussions on correlation between the dynamic resistance and the transport loss for the Bi-2223 tape.

• Journal of the Korean Magnetics Society
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• v.2 no.2
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• pp.145-149
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• 1992

The characteristics of electromagnetic devices with permanent magnet depends greatly on the remanence pattern of permanent magnet. So, it is necessary to analyze the pattern of remanence in permanent magnet. This paper presents a finite element analysis of magnetizer considering the nonlinearity and anisotropy of yoke and magnet in magnetizer. The distributions of magnetizations are obtained according to the variations of magnetizing currents for two kinds of magnetizers with different magnetizing poles. It is found that the excessive magnetizing current results in the reduction and polarity reversion of magnetization in the multi-pole magnetizing system where the pole angle is too small. During the design and analyzing of multi-pole magnetizer, it must be considered that there exists an optimal value of magnetizing current and pole angle of magnetizer.

• Progress in Superconductivity and Cryogenics
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• v.24 no.4
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• pp.29-35
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• 2022

We fabricated MHOS (multi-HTS layers on one substrate) high-temperature superconducting (HTS) REBCO conductors using HTS REBCO coated conductor (CC) A-specimen, which induces an artificial magnetic flux pinning effect, and HTS REBCO CC B-specimen, that does not induce this effect. The superconducting magnetic properties of the fabricated MHOS conductors were examined by measuring their magnetic moment m(H) curves using a physical property measurement system (QD PPMS-14). The critical current density (J_c) characteristics of our four-layered MHOS HTS REBCO conductor specimens such as BAAB, BBBB, and AAAA were lower than those of their two-layered and three-layered counterparts. At a temperature T of 30 K the magnetic flux pinning physical indicator δ values (obtained from the relationship J_c ∝ H^-δ) of the three-layer ABA (δ = 0.35) and two-layer AB (δ = 0.43) specimens were found to be significantly lower than those of the four-layer ABBA (δ = 0.51), BAAB (δ = 0.60), AAAA (δ = 0.78) and BBBB (δ = 0.81) structures.

• Tribology and Lubricants
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• v.23 no.6
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• pp.283-287
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• 2007

Permanent-magnet (PM) passive bearings use the repulsive forces between the rotor and the stator magnets for the bearing function. It is desirable that the stiffness of the bearing is maximized with the given volume of the magnet. The stiffness is affected by the magnet strength, the number of layers, and the magnetization patterns. Previously, finite-element method (FEM) has been used to maximize the stiffness of the bearing. In this paper, we used the equivalent current sheet method to calculate the stiffness. The validity of this approach is checked against FEM results. The optimized bearing is applied to a micro flywheel energy storage system.

• Progress in Superconductivity
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• v.14 no.2
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• pp.102-105
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• 2012

We are developing meander-shaped metallic magnetic calorimeters using micro-fabrication methods. A planar Nb coil in a meander shape was fabricated on a Si substrate. The coil was designed to have a persistent current using a metal heater evaporated on a part of the coil. A paramagnetic sensor, $5{\mu}m$ thick Au:Er foil, was glued on top of the meander structure with epoxy. The magnetization and heat capacity were measured at different temperatures, and applied field currents matched well with expected values. The detector showed an energy resolution of 4 keV FWHM for the 5.5 MeV alpha particles.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.33 no.5
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• pp.167-172
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• 1984

This paper describes the finite element analysis of magnetostatic field problems with permanent magnets. Two kinds of algorithms, one using the magnetic vector potential and the other using the magnetic scalar potential, are introduced. The magnetization of the pemanent magnet is used as the source instead of the magnetic equivalent current in both of the formulations using the magnetic vector potential and the magnetic scalar potential. A simple functional, which has only the region integral instead of the region integral and boundary integral, is derived in the formulation using the magnetic scalar potential. These make the formulation of the system equations simpler and more convenient than the conventional methods. The numerical results by the two proposed algorithms for a C-type permanent magnet model are compared with the analytic solutions respectively. The numerical results are in good agreement with the analytic solutions.

• Progress in Superconductivity
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• v.9 no.1
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• pp.11-17
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• 2007

Magnetization studies have been carried out on $MgB_2$ polycrystalline samples in the temperature range of 5 - 44 K and in the magnetic field up to 7 Tesla. The critical current density was calculated from hysteresis loops using the Bean's critical state model, and the highest value of $J_c$ at 20 K was $2.7{\times}10^5\;A/cm^2$ at 2 Tesla. The hysteresis loops were carefully examined to determine the temperature and magnetic field range where flux jumps appeared. The first jump occurred typically at 1 Tesla. Due to the strong pinning, we observed the presence of flux jump below H = 1 Tesla at temperature below 30 K.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.64 no.3
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• pp.159-163
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• 2015

Recently squirrel cage induction generator has been steadily applied to many small hydro power plants. Induction generator needs a reactive power for magnetization. The reactive power of induction generator is being supplied from the supply side mostly. The use of induction generators in the power distribution grid can affect the power factor. The power factor of induction generator is fixed already during production. The power factor in the distribution system is due to the increase or decrease of the load rather than due to the induction generator. In this study, we analyzed that how the increase or decrease of D/L load impacts at the change of power factor and power flow.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.6
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• pp.1110-1115
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• 2009

We studied on the design of electrical parameters for ICP(Inductively Coupled Plasma) light sources which can be effective to improve the electrical power efficiency of it. These parameters were derivated from Barkhausen theory about the oscillating condition of a ballaster. The relationships of $f-I_p$ and f-n were calculated theoretically and then these relationships were compared with the measured results about $I_p$ and power depending to a discharge length(l) of ICP light source. Finally, we can see that a specific range of induced current depending to a discharge length would be necessary to minimize the change of magnetization inductance and driving frequency at driving.

• Journal of Magnetics
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• v.1 no.2
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• pp.94-100
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• 1996

A hysteresis loop tracer using a pulsed high magnetic field of 113.4 kOe, which is suitable for rare earth based permanent magnets, is constructed. The high pulsed magnetic field is generated by discharging a large capacitance charge (5 mF) with a voltage of 600 V into an air solenoid with the inner diameter of 14 mm, outer diameter of 36 mm and the lingth of 34 mm. A computer simulation method is used for the construction of an electromagnet to optimize the many parameters such as the discharge current, generated pulsed magnetic field intensity, thermal dissipation, capacitance, charged voltage, period of damping oscillation and solenoid geometry. By using the hysteresis loop tracer constructed in this work, we are able to measure hystersis loops of several rare earth based permanent magnets with large values of the remanent magnetization, coercvity and energy product.