• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 하계학술대회 논문집 A
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• pp.213-215
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• 2002

This paper proposes an advanced compensating algorithm of the secondary current of CTs. The exiting compensating algorithm for the current transformers calculates magnetic flux using the magnetization curve. In such a case, it is difficult to compensate for distorted secondary current when a remanent flux exists in a core at the beginning of the calculation. To make up for the drawback in the existing compensating algorithm, the algorithm detects the instant of saturation using difference of the secondary current and estimates flux at the instant of the beginning of the first saturation. After that, the algorithm calculates flux and compensates for distorted secondary current.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1998년도 하계학술대회 논문집 A
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• pp.325-327
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• 1998

Disk type single-phase switched reluctance motor which has an advantage of simple robust construction, simple control circuity, and low manufacturing cost has a specific property of axial flux machine and radial flux machine simultaneously. So, this DSPSRM has a complicated magnetic circuit and it is difficult to analyze characteristics of DSPSRM for design. In this paper, we used to analyze the effects of radial flux and axial flux simultaneously by 3D-finite element method. From the results of 3-D FEM, we obtained the approximated torque characteristics of DSPSRM. It's analysis results can be used in optimal design of DSPSRM considering the saturation.

• Transactions on Electrical and Electronic Materials
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• 제18권2호
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• pp.97-102
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• 2017

A current transformer (CT) is a type of sensor that consists of a combination of electric and magnetic circuits, and it measures large ac currents. When a large amount of current flows into the primary winding, the alternating magnetic flux in the iron core induces an electromotive force in the secondary winding. The characteristics of a CT are determined by the iron core design because the iron core is saturated above a certain magnetic flux density. In particular, when a large current, such as a current surge, is input into a CT, the iron core becomes saturated and the induced electromotive force in the secondary winding fluctuates severely. Under these conditions, the CT no longer functions as a sensor. In this study, the characteristics of the secondary winding were investigated using the time-difference finite element method when a current surge was provided as an input. The CT was modeled as a two-dimensional analysis object using constraints, and the saturation characteristics of the iron core were evaluated using the Newton-Rhapson method. The results of the calculation were compared with the experimental data. The results of this study will prove useful in the designs of the iron core and the windings of CTs.

• 전력전자학회논문지
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• 제11권4호
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• pp.340-348
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• 2006

본 논문에서는 동적전압보상기 (DVR)를 구성하기 위한 정합 변압기의 돌입전류 제어기법을 제안하였다. DVR 시스템은 배전계통에서 발생하는 순시적 전압강하를 보상하기 위한 직렬전압 주입장치로서, 임의의 전압을 생성하는 PWM 인버터와 전압 평활용 LC 수동필터 및 절연을 위한 정합 변압기 등으로 구성된다. 그러나 정합 변압기의 사용은 변압기내에서 자속 포화현상에 의하여 정격의 수배에 달하는 돌입전류가 발생하여 시스템의 절연파괴를 초래하고 이 때문에 변압기의 정격용량을 2 배 정도로 초과하여 사용하게 한다. 따라서 본 연구에서는 정합 변압기의 자속 포화현상에 따른 돌입전류의 크기를 분석할 수 있는 새로운 모델링 분석기법 및 돌입전류의 크기를 제한하는 자화전류 제어기법을 제안하였다. 모의실험 및 실험을 통하여 제안된 DVR 제어기법의 타당성을 입증하였다.

• 대한전기학회논문지:전력기술부문A
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• 제55권3호
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• pp.95-101
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• 2006

This paper proposes a modified current differential relay for $Y-{\Delta}$ transformer protection. The relay uses the same restraining current as a conventional relay, but the differential current is modified to compensate for the effects of the exciting current. A method to estimate the circulating component of the delta winding current is proposed. To cope with the remanent flux, before saturation, the core-loss current is calculated and used to modify the measured differential current. When the core then enters saturation, the initial value of the flux is obtained by inserting the modified differential current at the start of saturation into the magnetization cure. Thereafter, the core flux is then derived and used in conjunction with the magnetization curve to calculate the magnetizing current. A modified differential current is then derived that compensates for the core-loss and magnetizing currents. The performance of the proposed differential relay was compared against a conventional differential relay. Test results indicate that the modified relay remained stable during severe magnetic inrush and over-excitation, because the exciting current was successfully compensated. This paper concludes by implementing the relay on a hardware platform based on a digital signal processor. The relay does not require additional restraining signal and thus cause time delay of the relay.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2011년도 임시총회 및 하계학술연구발표회
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• pp.19-19
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• 2011

We studied the effect of Dy content on the magnetic properties of cobalt ferrite single crystal. The $CoFe_{1.9}Dy_{0.1}O_4$ single crystals were grown by the flux method by using $Na_2B_4O_{7.}10H_2O$ (Borax) as a solvent (flux). The black and shiny single crystals were obtained as a product. The X-ray diffraction test at room temperature confirmed the spinel cubic symmetry with lattice constant a = $8.42{\AA}$ of the single crystals. The presences of constitute elements (Co, Fe and Dy) was endorsedby EDAX analysis. The saturation magnetization (Ms) of $CoFe_{1.9}Dy_{0.1}O_4$ single crystals was measured and is found to be 72emu/g or equivalently $3.2{\mu}B$/f.u. at 300 K. The observed Ms and coercivity (Hc) is found to be lower than that of pure $CoFe_2O_4$.

• 비파괴검사학회지
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• 제22권2호
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• pp.177-186
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• 2002

본 논문에서는 3차원 형태의 결함을 가진 지하매설 가스관에서 누설자속(magnetic flux leakage, MFL) 탐상 법을 사용한 결함 검출에 관하여 연구하였다. 영구자석과 요크로 구성된 자기 시스템을 유한요소법을 사용하여 해석하고 동작점을 설정하였다. 가스관이 충분히 포화되지 않은 경우에는 측정이 곤란하며, 과대포화 된 경우에는 결함에 의한 누설자속의 변화량이 적어서 측정이 곤란하므로 적정한 값을 설정하여야 하므로 자기 시스템의 동작점은 결함이 있을 때 누설자속 증가율이 최대가 되도록 설정하여야 한다. 본 논문에서는 3차원 비선형 유한요소법을 사용하여, 가스관에 결함이 있는 경우 결합의 크기, 깊이에 따른 결함신호를 예측하여 그 결과 가스관 포화상태의 적절여부, 홀 센서 range 및 resolution의 적정도 등을 연구하였다. 또한 홀 센서의 민감도 형장을 위하여 back-yoke를 사용하여 측정신호를 향상시키는 방법을 제안하였다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 춘계합동학술대회 논문집
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• pp.11-20
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• 2002

본 논문에서는 3차원 형태의 결함을 가진 지하매설 가스관에서 누설자속(magnetic flux leakage, MFL) 탐상법을 사용한 결함 검출에 관하여 연구하였다. 영구자석과 요크로 구성된 자기 시스템을 유한요소법을 사용하여 해석하고 동작점을 설정하였다. 가스관이 충분히 포화되지 않은 경우에는 측정이 곤란하며, 과대포화된 경우에는 결함에 의한 누설자속의 변화량이 적어서 측정이 곤란하므로 적정한 값을 설정하여야 하므로 자기 시스템의 동작점은 결합이 있을 때 누설자속 증가율이 최대가 되도록 설정하여야 한다. 본 논문에서는 3차원 비선형 유한요소법을 사용하여, 가스관에 결함이 있는 경우 결함의 크기, 깊이에 따른 결함신호를 예측하여 그 결과 가스관 포화상태의 적절여부, 홀 센서 range 및 resolution의 적정도 등을 연구하였다. 또한 홀 센서의 민감도 향상을 위하여 back-yoke를 사용하여 측정신호를 향상시키는 방법을 제안하였다.

• 전기학회논문지P
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• 제53권2호
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• pp.51-57
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• 2004

Vector control schemes are used in inverter-fed induction motor drives to obtain high performance. Crucial to the success of the vector control scheme is the knowledge of the instantaneous position of the rotor flux. However, the position of the rotor flux change with temperature and magnetic saturation of the motor. This variation cause deterioration of both steady state and dynamic operation of the motor drives. Performance degradation is in the form of input-output torque nonlinearity and saturation of the motor. Analytic expressions are derived to evaluate the effects due to parameter sensitivity. Also, dynamic response is shown by speed command with the variation of stator and rotor resistance.

• Journal of Magnetics
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• 제15권4호
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• pp.199-203
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• 2010

This paper discusses the effectiveness of high magnetization saturation in ILI (In-Line Inspection) using an MFL (Magnetic Flux Leakage) tool, and introduces a practical method for improving the magnetization level together with the piggability. Thin steel plates, replacing the conventional wire brushes were used as conductors to transfer the magnetic flux to the pipe wall. The newly designed MFL tool was compared with the conventional version by means of FEM (Finite Element Method) analysis and full-scale experiments. In the results, the newly developed magnetization system obtained a stronger MFL signal amplitude, specially 2.7 times stronger, than that obtained by the conventional magnetization system for the same defect dimensions.