• 한국재료학회지
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• 제23권6호
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• pp.309-315
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• 2013

$GdBa_2Cu_3O_{7-y}$(Gd123) powders were synthesized by the solid-state reaction method using $Gd_2O_3$ (99.9% purity), $BaCO_3$ (99.75%) and CuO (99.9%) powders. The synthesized Gd123 powder and the Gd123 powder with $Gd_2O_3$ addition ($Gd_{1.5}Ba_2Cu_3O_{7-y}$(Gd1.5)) were used as raw powders for the fabrication of Gd123 bulk superconductors. The Gd123 and Gd1.5 bulk superconductors were fabricated by sintering or a top-seeded melt growth (TSMG) process. The superconducting transition temperature ($T_{c,onset}$) of the sintered Gd123 was 93 K and the transition width was as large as 20 K. The $T_{c,onset}$ of the TSMG processed Gd123 was 82 K and the transition width was also as large as 12 K. The critical current density ($J_c$) at 77 K and 0 T of the sintered Gd123 and TSMG processed Gd123 were as low as a few hundreds A/$cm^2$. The addition of 0.25 mole $Gd_2O_3$ and 1 wt.% $CeO_2$ to Gd123 enhanced the $T_c$, $J_c$ and magnetic flux density (H) of the TSMG processed Gd123 sample owing to the formation of the superconducting phase with high flux pinning capability. The $T_c$ of the TSMG processed Gd1.5 was 92 K and the transition width was 1 K. The $J_cs$ at 77 K (0 T and 2 T) were $3.2{\times}10^4\;A/cm^2$ and $2.5{\times}10^4\;A/cm^2$, respectively. The H at 77 K of the TSMG-processed Gd1.5 was 1.96 kG, which is 54% of the applied magnetic field (3.45 kG).

• 한국초전도ㆍ저온공학회논문지
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• 제23권3호
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• pp.45-50
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• 2021

In this study, the effect of the size of B powder on the critical current density (J_c) of MgB₂ prepared by an in situ reaction process was investigated. Various combinations of B powders were made using a micron B, ball-milled B and nano B powders. Micron B powder was reduced by ball milling and the milled B powder was mixed with the micron B or nano B powder. The mixing ratios of the milled B and micron or nano B were 100:0, 50:50 and 0:100. Non-milled micron B powder was also mixed with nano powder in the same ratios. Pellets of (2B+Mg) prepared with various B mixing ratios were heat-treated to form MgB₂. T_c of MgB₂ decreased slightly when the milled B was used, whereas the J_c of MgB₂ increased with increasing amount of the milled B or the nano powder. The used of the milled B and nano B power promoted the formation MgB₂ during heat treatment. In addition to the enhanced formation of MgB₂, the use of the powders reduced the grain size of MgB₂. The use of the milled and nano B powder increased the J_c of MgB₂. The highest J_c was achieved when 100% nano B powder was used. The J_c enhancement is attributed to the high volume fraction of the superconducting phase (MgB₂) and the large grain boundaries, which induces the flux pinning at the magnetic fields.

• 한국자기학회지
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• 제25권4호
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• pp.123-128
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• 2015

철은 강도와 경도가 높고 전기전도도가 훌륭한 원소이며, 또한 가공이 쉽기 때문에 다양한 분야에서 사용되고 있다. 교량에서는 큰 하중이면서도 경량화를 위하여 강철선으로 된 텐던이 사용되고 있다. 철이 구조용 강으로 사용될 경우 중요한 문제 중 하나인 안전 진단을 위해서는 비파괴 검사(Non-Destructive Testing)가 필수적인데 철강의 자기적 특성이 비선형의 자화곡선과 이력(hysteresis)현상이 있는 자기이력곡선으로 인하여 비파괴 검사에 적용이 어렵다. 본 연구에서는 교량에 부착되어 있는 텐던의 인장변형력을 비파괴 적이면서 자기적인 방법으로 측정하기 위한 기초 연구로, 텐던의 인장변형력에 의한 자기이력 특성변화를 관찰하기 위하여 직경 15.5 mm의 7-strand 텐던에 인장력을 0에서 2 GPa까지 인가할 수 있는 자기이력곡선 측정 장치를 제작하였다. 제작 된 자기이력곡선 측정 장치를 이용하여 시판되고 있는 두 제조회사의 텐던에 대하여 자기적 특성을 조사하였고, 인장변형력에 따른 자기적 특성의 변화가 가장 큰 부분은 자기이력곡선 상의 knee 부분 근처에서의 상대 진폭투자율로 500에서 200까지 감소하였으며 최대 자속밀도 또한 0.6 T 정도로 변화하였다. 텐던의 인장변형력을 측정하는 방법으로 knee 부분의 진폭투자율 측정뿐만 아니라 최대 자속밀도의 측정방법도 가능할 것으로 생각된다.

• 전기학회논문지
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• 제57권11호
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• pp.1962-1969
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• 2008

According to the increase of power demand and expansion of downtown, it is necessary to install transformers additionally in operating substations and construct substations in residential area. But the public complaint is increased due to the transformer noise of the substation. KEPCO has used a vibration preventing pad, various soundproof walls and an encloser to transformers in outdoor substations, and a soundproof door, shutter and wind-path soundproof equipment in indoor substations to block the sound propagation of the transformers. But these noise reduction methods are not satisfied. It should be considered to reduce transformer noise itself. In this paper, we investigated core noise reduction techniques to develope a low noise transformer. The techniques to reduce core noise of the transformer are application of high permeability grain oriented silicon sheets, decrease of magnetic flux density of core, application of 6step-lap core stacking method, improvement of core binding method(binding addition, band fixing) and application of rubber damper in oder to reduce transmission of core vibration, etc.

• 조명전기설비학회논문지
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• 제17권6호
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• pp.127-129
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• 2003

최근 차세대 고용량 저장 매체 뿐 아니라 다양한 멀티미디어를 구현할 수 있는 디지털 다기능 디스크(DVD)의 개발에 가전 및 컴퓨터 업계의 노력이 집중되고 있다. 현재 국내에서 제작되고 있는 DVD 구동 모터용 마그네트는 소결 자석 부품을 조립하여 제작하고 있으며 조립에 따른 진동 및 소음 절감에 한계가 있다. 따라서 본 연구에서는 이 회전자를 일체형으로 제작함으로써 조립에 따른 가공 공차를 줄여 진동 및 소음을 줄이고자 한다. 이때 일체형으로 제작하기 위해서는 제품을 자장 중에서 사출해야 되며, 이 사출용 금형을 유한요소법을 이용하여 설계하고 이를 통한 제품의 특성을 실험치와 비교하였다.

• Journal of Electrical Engineering and Technology
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• 제10권2호
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• pp.545-550
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• 2015

High Temperature Superconducting (HTS) synchronous generators can be designed with either an air-core type or iron-core type. The air-core type has higher efficiency under rated rotating speed and load than the iron-core type because of the iron losses which may produce much heat. However, the total length of HTS wire in the air-core type is longer than the iron-core type because the generated magnetic flux density of the air-core type is low. This paper deals with designs of 10 MW air-core and iron-core HTS wind power generators for wind turbines. Fully air-core, partially iron-core, and fully iron-core HTS generators are designed, and various stator winding methods in the three HTS generators are also considered, such as short-pitch concentrated winding, full-pitch concentrated winding, short-pitch distributed winding, and full-pitch distributed winding. These HTS generators are analyzed using a 3D finite elements method program. The analysis results of the HTS generators are discussed in detail, and the results will be effectively utilized for large-scale wind power generation systems.

• 대한기계학회논문집A
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• 제26권7호
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• pp.1232-1240
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• 2002

Recently, linear motors are applied to many small precision products. Thus high generating power with small size is required of it. In order to increase the motor efficiency, the design variables need to be optimized. In this study, Vector Fields FEM software, OPERA-3d, was used for simulating linear motor. The thrust and magnetic flux density at the air-gap center were simulated and compared with the experimental results. Taguchi method was applied to investigate the effects of each variables. As a result, the thickness of conductor and magnet was important for the thrust but the thickness of the yoke. The temperature of the conductor was determined by finding the thermal conductivity that was determined by experimentation. Correlation equation relating to the thrust and temperature was proposed by Latin square and Least Square method. The optimum design variables were determined by correlation equation, and compared with simulation results. According to this analysis, thrust force of linear motor was improved about 7% comparing with conventional model.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.479-482
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• 2008

In order to more closely examine the vacuum arc phenomena, it is necessary to predict the magnetohydrodynamic (MHD) characteristics by the multidisciplinary numerical modeling, which is coupled with the electromagnetic and hydrodynamic fields, simultaneously. In this study, the thermal-fluid characteristics of high current vacuum arcs were calculated by a commercial multiphysics package, ANSYS, in order to obtain Joule heat, Lorentz force and the interactions with flow variables. We assumed the diffused-mode arc within an AMF vacuum interrupter. It was found with four different currents that the temperature distributions on the anode surface are diffused uniformly without concentration in 7kA for both types (cup and coil-type). But the arc plasma transition and an increase of thermal flux density for increasing the applied current have caused the change of temperature distributions on the anode surface. We should need further studies on the two-way coupling method and radiation model for arc plasmas in order to accomplish the advanced analysis method for multiphysics.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1995년도 추계학술대회 논문집
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• pp.30-36
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• 1995

This paper proposed on the effective cutting conditions of cage motor rotor by turning. If you want to introduce automatic manufacturing system into the cutting process of cage motor rotor, the selections of effective cutting conditions are necessary. The cutting process of cage motor rotor requires the precision and the out of roundness of cage motor rotor. The surface roughness of cutting face. it is very important factor with effect on the magnetic flux density of cage motor rotor. The purpose of this study is to find out the effects of cutting condition. upon adapting this results, we will improve the production rate in the cutting process of cage motor rotor. As a result, the selection of cutting conditions are important factors to production rate. And these are chosen by the investigations of cutting characters and surface roughness. The experimental result, showed that the increase of cutting speed caused the decrease of cutting force and the high surface integrity. The increase of feed rate and increase of depth of cut caused the increase of cutting force and surface roughness. Thus, the effective cutting conditions of cage motor rotor by turing are cutting speed 291m/min, feed rate 0.10mm/rev, depth of cut 0.05mm.

• Journal of Magnetics
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• 제19권2호
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• pp.130-139
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• 2014

This paper focuses on the modeling and analysis a novel two-axis rotary normal-stress electromagnetic actuator with compact structure for fast steering mirror (FSM). The actuator has high force density similar to a solenoid, but its torque output is nearly a linear function of both its driving current and rotation angle, showing that the actuator is ideal for FSM. In addition, the actuator is designed with a new cross topology armature and no additional axial force is generated when the actuator works. With flux leakage being involved in the actuator modeling properly, an accurate analytical model of the actuator, which shows the actuator's linear characteristics, is obtained via the commonly used equivalent magnetic circuit method. Finally, numerical simulation is presented to validate the analytical actuator model. It is shown that the analytical results are in a good agreement with the simulation results.