• Structural Engineering and Mechanics
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• v.20 no.3
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• pp.363-380
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• 2005

The cable tension plays an important role in the construction, assessment and long-term health monitoring of cable structures. The cable vibration equation is nonlinear if cable sag and bending stiffness are included. The engineering implementation of a vibration-based cable tension evaluation is mostly carried out by the simple taut string theory. However, the simple theory may cause unacceptable errors in many applications since the cable sag and bending stiffness are ignored. From the practical point of view, it is necessary to have empirical formulas if they are simple and yet accurate. Based on the solutions by means of energy method and fitting the exact solutions of cable vibration equations where the cable sag and bending stiffness are respectively taken into account, the empirical formulas are proposed in the paper to estimate cable tension based on the cable fundamental frequency only. The applicability of the proposed formulas is verified by comparing the results with those reported in the literatures and with the experimental results carried out on the stay cables in the laboratory. The proposed formulas are straightforward and they are convenient for practical engineers to fast estimate the cable tension by the cable fundamental frequency.

• Parasites, Hosts and Diseases
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• v.41 no.3
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• pp.175-177
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• 2003

An ELISA was established to measure bovine IgG directed against the recombinant antigenic determinant of Nc-p43, a major surface antigen of Neospora caninum. In a previous study, two thirds of the C-terminal of the molecule was expressed as a $6{\;}{\times}{\;}His$ tagged protein (Ncp43p) for ELISA using 2/3 of the N-terminal of SAG1 from Toxoplasma gondii as a control (TgSAG1A). Among 852 cattle sera collected from stock farms scattered nation-wide, 103 sera (12.1％) were found to react with Ncp43p positively, but no positive reaction was observed with TgSAG1A. This study shows that Ncp43p could be available as an efficient antigen for the diagnosis of neosporosis in cattle. Furthermore, it together with TgSAG1A, could be useful for the differential diagnosis of N. caninum and T.gondii infections in other mammals.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.20 no.3
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• pp.6-11
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• 2006

This paper describes the novel control techniques design of VSC(Voltage Sag Corrector) for the purpose of power line quality enhancement. A fast detecting technique of voltage sag is implemented through the detection of instantaneous value on synchronous rotating dq-reference frame. The first order digital filter is added in the detection algorithm to protect the insensitive characteristics against the noise. The relationship between the total detection time and cut-off frequency of the filter is described. The size of the capacitor bank used as the energy storage element is designed from the point of view of input/output energy with circuit analysis. Finally, the validity of the proposed scheme is proven through the simulated results.

• Journal of Electrical Engineering and Technology
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• v.12 no.3
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• pp.1016-1026
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• 2017

An adaptive extended Kalman filter based on the maximum likelihood (EKF-ML) is proposed for detecting voltage sag in this paper. Considering that the choice of the process and measurement error covariance matrices affects seriously the performance of the extended Kalman filter (EKF), the EKF-ML method uses the maximum likelihood method to adaptively optimize the error covariance matrices and the initial conditions. This can ensure that the EKF has better accuracy and faster convergence for estimating the voltage amplitude (states). Moreover, without more complexity, the EKF-ML algorithm is almost as simple as the conventional EKF, but it has better anti-disturbance performance and more accuracy in detection of the voltage sag. More importantly, the EKF-ML algorithm is capable of accurately estimating the noise parameters and is robust against various noise levels. Simulation results show that the proposed method performs with a fast dynamic and tracking response, when voltage signals contain harmonics or a pulse and are jointly embedded in an unknown measurement noise.

• Proceedings of the KIPE Conference
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• 2001.10a
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• pp.502-507
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• 2001

This paper proposes a novel detection algorithm of faulted voltages under the unbalanced condition. To quantify the standard of unbalance under the faulted conditions, the 3-phase unbalanced voltages are decomposed into two balanced 3-phase symmetrical components of the positive and negative sequence voltages, which is defined by the magnitude factor (MF) and unbalance factor (MF). It is analyzed that MF and UF values are given as the dc constant values even though unbalance condition. This paper also proposes the control scheme of the instantaneous voltage sag corrector based on this detection algorithm. The validity of the proposed algorithm is verified through the EMTDC simulation and experiments.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.64 no.3
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• pp.104-110
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• 2015

This paper describes a power quality disturbance generator for the test of a microgrid. The generator provides phase-angle jump as well as voltage sag with simple structure. The main components of the generator are SCR thyristors and transformers, therefore, high reliability and high efficiency can be obtained without switching losses. The operating principle of the proposed scheme is described and the voltage and current characteristics in case of voltage sag with phase-angle jump is analyzed. The usefulness of the proposed topology is verified through simulations and experimental results.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.53 no.12
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• pp.678-684
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• 2004

Automatic reclosing is a typical protection method in power distribution systems for clearing the temporary faults. However, it has a fatal weakness in regards to voltage sags because it produces successive voltage sags. In this paper, we explored successive impact of voltage sag due to the automatic reclosing of power distribution systems. The actual tests of low voltage loads were accomplished for obtaining the susceptibility of voltage sags. The final results of the test yielded power acceptability curves of voltage sag, and the curves were transformed the 3-dimensional CBEMA(Computer Business Equipment Manufacturer Association) format. For the quantitative evaluation of the impact of successive voltage sags, an assessment formulation using the voltage sag contour was proposed. The proposed formulation was tested by using the voltage sag contour data of IEEE standard and the results of the test. Through the case studies, we verified that the proposed method can be effectively used to evaluate the actual impact of successive voltage sans.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.2
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• pp.174-184
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• 2013

For the successful R&D and deployment of LED-based green energy lighting systems, the real-time power quality measurement of both various non-linear power signals including pulse waveform, spike waveform, etc and the undesired-signals including harmonics, sag, swell, etc is required. In this paper, we propose a low-cost power quality measurement (PQM) method for low- (60Hz-several KHz) to high-frequency (several tens KHz) power signals, which are generated by green-energy lighting systems, and implement a PQM testbed using TI TMS320F28335 MCU. The proposed algorithm is programmed using C in the CCS (Code Composer Studio) 3.3 environment and is verified using test signals generated by an arbitrary signal generator, NF-WF1974. In the implemented testbed, we can measure various non-linear current signals that LED SMPS generates, analyze harmonics by fast Fourier transform, and test sag, swell, and interruption using wavelet transform.

• Proceedings of the KIPE Conference
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• 2013.07a
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• pp.345-346
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• 2013

본 논문에서는 단상 1.9kV/127V, 2kVA 용량의 양방향 지능형 반도체 변압기의 시작품을 제작하고 그 동작특성을 실험적으로 분석한 내용을 기술하고 있다. 제작한 반도체 변압기는 3대의 LLC 컨버터를 입력 측은 직렬로 결합하고 출력 측은 병렬로 결합한 AC-DC 컨버터와 1대의 하드스위칭 양방향 2-Stage DC-AC 컨버터가 직렬로 결합되어 있다. 제안하는 반도체변압기의 회로적인 특성을 분석하기 위해 PSCAD/EMTDC 소프트웨어를 이용한 시뮬레이션을 실시하였고 분석을 통해 얻은 결과를 바탕으로 하드웨어 시작품을 제작하고 다양한 실험을 통해 그 동작과 성능을 검증하였다. 먼저 1차적으로는 정상동작에 대해 실험을 실시하고 얻은 결과를 시뮬레이션 결과와 비교 분석하였다. 2차적으로는 전력의 흐름에 따른 동작을 실험적으로 분석하였다. 그 후에는 입력전압에 외란이 발생하였을 때 보상성능을 순방향 조류와 역방향 조류 2가지 경우로 나누어 실험을 실시하고 그 결과를 실험결과와 비교 분석하였다. 분석한 결과 제안하는 반도체변압기는 양방향 전력흐름이 가능하고 입력전압에 Sag가 발생한 경우에도 이를 보상하여 수전단이나 부하에 전력공급이 가능함을 알 수 있었다. 향후 단상 반도체 변압기 2대를 더 제작하여 3상 3.3kV/380V, 6kVA 용량으로 확대하여 실험을 실시할 예정이다.

• Proceedings of the KIEE Conference
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• 2015.07a
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• pp.203-204
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• 2015

본 논문은 실제 전력계통을 모의한 A계통에서 3상 지락 사고가 발생하였을 때, 순시 전압강하를 보상하기 위한 동적전압보상기(Dynamic Voltage Restorer)의 동작에 따른 해당 부하의 영향성을 연구하였다. 동적전압보상기의 동작을 위한 전압강하 검출은 RMS Detection 기법을 통해 구현하였으며, IEEE Standard 1159-1995의 기술된 Voltage Sag의 정의에 따라 동적전압보상기의 on/off 제어를 수행하였다. A계통 모델링을 포함한 모든 시뮬레이션은 PSCAD/EMTDC 상에서 구현하였으며, RMS 전압 측정 및 Voltage Sag 검출 신호, 그리고 동적전압보상기의 동작 전 후에 따른 순시 부하전압 파형을 결과로 다룰 것이다.