• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.2
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• pp.227-232
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• 2007

The autoreclosing is applied to power system for maintaining system stability and continuity of supply. Developments on distributed generation(DG) grows significantly by environmental issues and economical issues. If the DG is connected to distribution system, the DG influences the technical aspects such as power quality, protection and stability. It causes the challenges to protection, especially to reclosing. In order to achieve reliability and safety of the distribution system, the rules and guidelines suggest that the DG units should be rapidly disconnected from the network before the reclosing. If the DG is disconnected whenever the fault occurs, it cannot be utilized effectively. This paper presents the adaptive reclosing algorithm considering the DG. The algorithm consists of angle oscillation's judgment, EEEAC(Emergency Expanded Equal-Area Criterion), calculation of optimal reclosing time and re-connection algorithm. The simulation is implemented for the DG technology by using EMTP MODELS. The simulation results show that the transient stability is maintained and the DG is protected against disturbance.

• Journal of Electrical Engineering and Technology
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• v.10 no.3
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• pp.795-803
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• 2015

Autoreclosure provides a means of improving power transmitting ability and system stability. Conventional reclosure adopts the fixed dead time interval strategy, where the reclosure is activated after a time delay to restore the system to normal as quickly as possible without regard to the system conditions. However, these simple techniques cannot provide optimal operating performance. This paper presents an adaptive autoreclosure algorithm including variable dead time, optimal reclosure, phase-by-phase reclosure and emergency extended equal-area criterion (EEEAC) algorithm in order to improve system stability. The reclosure algorithm performs the operations that are attuned to the power system conditions. The proposed adaptive reclosure algorithm is verified and tested using ATP/EMTP MODELS, and the simulation results show that the system oscillations are reduced and the transient stability is enhanced by employing the proposed adaptive reclosure algorithm.

• Proceedings of the KIEE Conference
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• 1999.11b
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• pp.258-260
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• 1999

The Single Machine Equivalent(SIME) is a hybrid method resulting from the coupling of a time-domain program with the equal-area criterion. This paper presents the efficient filtering algorithm using improved SIME for Transient Stability Assessment. The main feature of the method is cascading contingency filtering. First contingency filtering is conducted by using the first-swing stability of equivalent One Machine Infinite Bus(OMIB) system. This stability is evaluated by checking its time trajectory. Selected cases through the first step are assessed on the second step using SIME under the detailed model of power systems. The efficiency of the algorithm is tested on PSS/E test system.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.52 no.12
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• pp.698-704
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• 2003

Autoreclosure provides a mean of improving power transmitting ability and system stability. The conventional reclosure adopts the fixed dead time interval strategy, that is, the reclosure is activated after a time delay to restore the system to normal as quickly as possible without regard to the system conditions, however, these simple techniques cannot give the optimal operating performance. For this reason, various adaptive reclosure algorithms have been proposed recently, This paper presents an adaptive autoreclosure algorithm including the variable dead time, optimal reclosure, sequential reclosure and emergency extended equal-area criterion (EEAC) algorithm in order to improve the system stability. The reclosure algorithm performs out the operations that are attuned to the power system conditions. The proposed adaptive reclosure algorithm is verified and tested by using EMTP MODELS, and the simulation results show that the system oscillations are reduced and the transient stability is enhanced by employing the proposed adaptive reclosure algorithm.

• Proceedings of the KIEE Conference
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• 2003.07a
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• pp.335-337
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• 2003

The protection against transient instability and consequent out-of-step condition is a major concern for the utility. The unstable system may cause serious damage to system elements such as generators and transmission lines. Therefore, out-of-step detection is essential to operate a system safely. This paper presents the Out-of-Step detection algorithm using voltage frequency variation. The digital filters based on Discrete Fourier Transforms (DFT) to calculate the frequency of a sinusoid voltage are used, and the generator angle is estimated using the variation of the calculated voltage frequency. The proposed out-of-step algorithm is based on the assessment of a transient stability using equal area criterion. The proposed out-of-step algorithm is verified and tested by using EMTP MODELS.

• Proceedings of the KIEE Conference
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• 2003.11a
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• pp.119-121
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• 2003

전력계통에 대해 적용되고 있는 수많은 안정화 방안으로 발전기 탈락, 부하차단, 계통분리 등의 방법 중에서, 우리나라 계통에서의 과도안정도 문제에 대한 안정화 대책으로는 주로 발전기 탈락이 많이 적용되어 왔다. 본 논문은 이러한 발전기 탈락량에 관한 주제를 다루고 있다. 이러한 발전기 탈락을 적용하기 위해서 과도안정도 취약지점에 대해 KPX 보고서를 참조하여 상정사고 지점을 선정하고, 해당지역 계통에 대해 등면적법을 적용, 적정 발전기 탈락량을 계산하였다. 이러한 사전 연산형(offline) 형 발전기 탈락 외에도 온라인 상에서의 발전기 탈락량 계산방법과 그 문제점에 대해서도 고려하였다.

• The Journal of Fisheries Business Administration
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• v.15 no.1
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• pp.58-80
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• 1984

The classification of islands is prerequisite for establishing a development policy to vitalize many-sided function of islands. We try to classify the 440 inhabited islands which exist in Jeon-Nam area and Kyong-Nam area by means of PCA. PCA begins with making correlation matrix of orignal variables. From this matrix we can comprehend the rough relationships between two variables. Next, we look for the eigenvalues which are roots of characteristic equation of correlation matrix. The number of eigenvalues is equal to that of original variables. We choose the largest eigenvalue λ$_1$among them and then look for the eigenvector of correlation matrix corresponding to the largest eigenvalue. Linear combination of eigenvector obtained above and original variables is namely first Principal Component (PC). Using an eigenvalue criterion(λ$\geq$ 1), we choose 3 PCs in Jeon-Nam area and 2 PCs in Kyong-Nam area. But we decide to consider only two PCs in both areas to faciliate a comparative analysis. Now, loss of information is 31.7% in Jeon-Nam area and 26.64% in Kyong-Nam area. PCs extracted by preceding procedure have characteristics as follows. The first PC relates to aggregate size of islands in case of both areas. The second PC relates to income per household, factors of agricultural production and factors of fisheries production in Jeon-Nam area, but in Kyong-Nam area it means distance from island and income per household. A classification of islands can be attained by plotting component scores of each island in graph used two PCs as axes and grouping similiar islands. 6 groups are formed in Jeon-Nam area and 5 groups in Kyong-Nam area. The result of this study in kyong-Nam area accords with prior result of study.

• Journal of the Korean housing association
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• v.22 no.3
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• pp.93-100
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• 2011

The objective of this study is to provide basic objective data which can be utilized as an adjustment criterion for the alleviation of the limit on the number of floors of buildings by quantitatively evaluates the effect of the alleviation of the limit on the number of floors of buildings in apartment complexes on thermal environment of apartment complexes using data obtained from apartments in a class 2 general residential area. In this study, we carried out a thermal environment analysis utilizing the simulation of a virtual object area. The result is summarized as follows: The result of analyzing the entire surface temperature showed an equal decrease of surface temperature due to shadow in all scenarios and high floors showed a tendency of low surface temperature during daytime as the rate of shadow the high floors increase. This influences not only the surface temperature but also HIP and is judged to greatly contribute to the alleviation of the heat island effect. Also, the reason why HIP at high floors shows high values before sunrise and after sunset is thought to be because the concrete wall of the building maintains a high temperature during nighttime by absorbing and storing sunlight during daytime instead of reflecting it since it has low reflectance.

• Communications for Statistical Applications and Methods
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• v.16 no.2
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• pp.239-347
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• 2009

This paper presents Kolmogorov-Smirnov, mean difference, AUROC and AR, four well known statistics that have been widely used for evaluating the discriminatory power of credit rating models. Criteria for these statistics are determined by the value of mean difference under the assumption of normality and equal standard deviation. Alternative criteria are proposed through the simulations according to various sample sizes, type II error rates, and the ratio of bads, also we suggest the meaning of statistic on the basis of discriminatory power. Finally we make a comparative study of the currently used guidelines and simulated results.

• Journal of Electrical Engineering and Technology
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• v.11 no.3
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• pp.543-550
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• 2016

The Active Superconducting Current Controller (ASCC) is a new type of Superconducting Fault Current Limiters (SFCL) which can limit the fault current in different modes. It also has the particular abilities of compensating active and reactive powers for electrical networks. In this paper, it is confirmed that the performance of ASCC in different operating modes introduces a limiting impedance in series with the network which can even degrade the transient stability and the operation of the Over-Current Relays (OCR) employed in a power system. In addition, the model of a three-phase ASCC is simulated, and the effect of descriptive modes on the current limiting level is investigated. For the transient stability analysis, a single machine-infinite bus system is tested, and the effect of operation modes is studied based on an equal area criterion obtaining the critical time and the critical angle. Modifying the setting parameters of OCR such as time dial and pick-up current, the protective coordination is also studied in different operating modes.