• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2005년도 하계학술대회 논문집 Vol.6
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• pp.288-289
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• 2005

As high temperature superconductor applications became a reality due to increase in coated conductor performance, it is important to understand their stability behavior to design safe electrical power systems. We have experimentally studied the dependence of quench and recovery characteristics of coated conductors on the amplitude of current and duration time. The sample used in the present study is stabilized with stainless steel. Stability tests of 3 cm long sample were performed in a liquid nitrogen bath cooling condition by applying a short period over current pulses for 50 and 100 ms, with amplitude up to ~ 6 times of the critical current. The transport current that follows before and after the current pulse was fixed about ~85% the critical current. We analyzed the quench recovery using the current voltage characteristic.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 학술회의 논문집 정보 및 제어부문 B
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• pp.720-723
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• 2003

Electric stimulation of teeth is used for assessing pulp vitality. Because of very high and wide range of impedance of the enamel, electric pulp testers use high voltage, high output impedance and alternative current source. Most pulp testers use voltage stimulation method and their stimulating threshold levels significantly depend on each individual. Therefore, a constant current stimulator is necessary to minimize the effect of wide variation in enamel thickness. In this study, we constructed a constant current source type of pulp tester with the maximum current of 150 uA.

• 한국지반환경공학회 논문집
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• 제11권11호
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• pp.63-75
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• 2010

중금속으로 오염된 부지는 다양한 공법으로 복원이 가능하나 오염부지가 비교적 넓은 경우 중금속을 부지로부터 제거하는 적극적 공법은 기술적 어려움과 비용의 문제로 쉽게 사용할 수 없다. 그러므로 토양에서 중금속의 용출을 차단 및 지연하는 안정화 공법이 보다 현실적이라 할 수 있다. 본 연구에서는 국내의 비교적 큰 규모의 중금속 오염토양인 제련소 오염토양을 대상으로 magnetite, hematite, zeolite-A, zeolite-X, zeolite-Y, zinc oxide, calcium oxide, carbon trioxide, manganese oxide, manganese dioxide, fish bone, sodium phosphate 등의 다양한 안정화제의 적용성실험을 수행하였다. 비소, 납, 구리, 니켈, 아연 등의 다중 중금속으로 오염된 토양의 경우 1종의 안정화제로 안정화가 어려우며 기존 연구에서 보고된 특정 중금속의 안정화에 우수한 성능을 갖는 안정화제의 경우에도 다른 중금속의 안정화에 기여하지 못하거나 용출을 촉진하는 경향을 보였다. 시간이 경과함에 따라 안정화 효율이 증가하였다. 니켈과 납의 경우 calcium oxide, carbon trioxide, manganese oxide 등의 안정화제가 효과가 있으며 특히 연속추출에서 물에 의한 추출부분에서 안정화 효율이 높았다. 구리의 경우 manganese oxide, zeolite 등이 효과가 크며 연속추출에서 exchangeable 추출부분에서 안정화 효율이 높았다. 비소의 경우 magnetite에 의한 안정화 효과를 보이며 대부분의 metal oxide와 phosphate 에 의해 용출이 촉진되는 부작용을 보였다. 그러므로 다양한 중금속으로 오염된 토양의 경우 2종 이상의 안정화제를 사용하여야 하며 역효과를 일으키는 안정화제의 사용을 배제하고 중금속의 농도에 따라 사용량 및 안정화 기간을 달리하여야 할 것으로 판단된다.

• 한국초전도ㆍ저온공학회논문지
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• 제24권4호
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• pp.40-45
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• 2022

The electrical/thermal stabilities and magnetic field controllability of a no-insulation (NI) high-temperature superconducting magnet are characterized by contact resistance between turn-to-turn layers, and the contact resistance characteristics are determined by properties of conductor surface and winding tension. In order to accurately predict the electromagnetic characteristics of the NI coil in a design stage, it is necessary to control the contact resistance characteristics within the design target parameters. In this paper, the contact resistance and critical current characteristics of a rare-earth barium copper oxide (REBCO) conductor were measured to analyze the effects of surface treatment conditions (roughness and oxidation level) of the copper stabilizer layer in REBCO conductor. The test samples with different surface roughness and oxidation levels were fabricated and conductor surface analysis was performed using scanning electron microscope, alpha step surface profiler and energy dispersive X-ray spectroscopy. Moreover, the contact resistance and critical current characteristics of the samples were measured using the four-terminal method in a liquid nitrogen impregnated cooling environment. Compared with as-received REBCO conductor sample, the contact resistance values of the REBCO conductors, which were post-treated by the scratch and oxidation of the surface of the copper stabilizer layer, tended to increase, and the critical current values were decreased under certain roughness and oxidation conditions.

• 조명전기설비학회논문지
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• 제16권2호
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• pp.45-53
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• 2002

본 논문은 두 지역 간에 직렬로 연결된 HVDC 연계시스템의 전력계통 안정화장치와 전력변환기의 적정 파라메터 선정기법을 다루었다. PSS파라메터 선정기법은 구하고자 하는 진상이 되도록 극좌표를 이동시키고, 충분한 댐핑을 얻도록 이득을 조절하는 고전적인 기법이다. 전력변환기의 적정 파라메터는 근궤적기법을 근거로 하여 기준 값의 변화와 시스템의 동요에 충분한 속응력과 안정도를 고려하여 산정한다. 이들 기법으로 구판 제정수로 소신호 및 과도안정도 분석결과는 사례연구시스템의 고유동요 주파수에 적절한 댐핑 효과를 보여주었다. 본 논문에서 사용한 프로그램은 MATLAB을 근거로 한 PST이다.

• 한국초전도ㆍ저온공학회논문지
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• 제11권1호
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• pp.1-4
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• 2009

Mechanical and electrical properties of silver stabilizer layer of coated conductor, which as prepared with nano silver paste as starting materials, have been investigated, Nano silver paste was coated on a YBCO film by dip coating process at a diping speed of 20m/min. Coated film was dried in air and heat treated at $400{\sim}700^{\circ}C$ in an oxygen atmosphere. Adhesion strength between YBCO and silver layer was measured by a tape est(ASTM D 3359). Hardness and electrical conductivity of the samples were measured by pencil hardness test (ASTM D 3363) and volume resistance test by LORESTA-GP (MITSHUBISHD, respectively. The sample heat-treated at $500^{\circ}C$ showed poor adhesion 1B, but samples heat treated at higher than $600^{\circ}C$ showed enhanced adhesion of 5B. The silver layer heat-treated at $700^{\circ}C$ showed the high hardness value larger than 9 H, low volume resistance, surface resistance value as well as superior current carrying capacity compared to sputtered silver. SEM observations showed that a dense silver layer was formed with a thickness of about $2{\mu}m$. Dip coated silver layer prepared by using nano silver paste showed superior electrical and mechanical characteristics.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2005년도 하계학술대회 논문집 Vol.6
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• pp.274-275
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• 2005

The tensile strain dependency of critical current in YBCO coated conductors was examined at 77K and in the self magnetic field. A commercially available YBCO sample with Cu stabilizer layer was supplied. There existed a peak in the relation between the Ie and tensile strain, and the reversible variation of $I_c$ with applied tensile strain was found. In the neutral axis Ni alloy RABiTS-$Y_2O_3$/YSZ/$CeO_2$ buffered YBCO tape, the $I_c$ recovered reversibly until the applied strain reached to about 0.5%, representing that a significant residual compressive strain induced during cooling to 77 K influenced the axial strain tolerance of YBCO conductors. To investigate the strain and stress influence on the $I_c$, the stress-strain characteristics of YBCO conductors measured at 77 K were discussed.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 1999년도 제1회 학술대회논문집(KIASC 1st conference 99)
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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.

• Transactions on Electrical and Electronic Materials
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• 제10권2호
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• pp.66-69
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• 2009

To manufacture YBCO-coated conductors as superconducting fault current limiters, it is important to conduct researches on their durability. To test their durability, it is necessary to investigate their properties before and after the quench in more severe conditions than in general operating conditions. In this study, their voltage-current and resistance properties were measured before and after a fault current was repetitively applied to them. For the applied voltage, the voltage grades of the YBCO coated conductors were considered. The current amplitude was controlled using protective resistance on an experimental track, and the time and number of applications were fixed to produce the quench occurrence at the fault angles of $0^{\circ}$, $45^{\circ}$, and $90^{\circ}$. The operating conditions of the YBCO coated conductors as the main components of superconducting fault current limiters were determined using their voltage properties. The voltage properties of the YBCO coated conductors that were analyzed in this research will be used as important data for their practical application to superconducting fault current limiters.

• 대한전기학회논문지:시스템및제어부문D
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• 제49권8호
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• pp.459-466
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• 2000

In this paper, we propose an attitude controller for an unstructured object using CMG(Control Moment of Gyro) subsystem, which has a stabilizer function. The CMG subsystem consists of one motor for spinning the wheel and the other motor for turning the outer gimbal. While the wheel of CMG subsystem is spinning at high speed, applying force to the spin axis of the wheel leads the torque about the vertical axis. We utilize the torque to control the attitude of object in this study. For the stabilizer function, in additiion, holding the load at the current position, the power applied to the gimbal motor of CMG will be cut, which result in the braking force to stop the load by gyro effect. However, due to the gear reduction connected to outer gimbal, slow load motion cannot generate the braking force. Thus, in this study, we are willing to make a holding force by applying control power to the gimbal motor from the signal of piezoelectric gyroscopic sensor that detected the angular velocity of the load. These two features are demonstrated in experiment, carrying a beam with crane. As a result, load was started to rotate by controlling gimbal positiion and was stopped by turning off the gimbal power. Moreover, slow movement of the load was also rejected by additional control with gyroscopic sensor.