• 조명전기설비학회논문지
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• 제29권4호
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• pp.54-61
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• 2015

Recently, DC-based power system is being paid attention as the solution for energy efficiency. As the example, HVDC (High Voltage DC) transmission system is utilized in the real power system. On the other hand, researches on LVDC (Low Voltage DC) distribution system, which are including digital loads, are not enough. In this paper, reliability in LVDC distribution system is analyzed according to the specific characteristics such as the arrangement of DC/DC converters and the number of poles. Furthermore, power quality is also taken account of since LVDC distribution system includes multiple sensitive loads and electric power converters. In order to achieve this, LVDC distribution systems are modeled using ElectroMagnetic Transient Program (EMTP) and both the minimal cut-set method and Customer Interruption Cost (CIC) are used in the reliability analysis.

• 조명전기설비학회논문지
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• 제29권9호
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• pp.51-58
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• 2015

Intelligent distribution automation system includes operating a switchgear of distribution system remotely when switchgear are not available to operate quickly. This system makes it possible to reduce the interrupt time. It also aims to improve the reliability of customers. Currently, Intelligent distribution automation improves the reliability by replacing manual switchgear, which is installed as sectional switchgear. However the prioritization of the replacement for the switchgear is required for its intellectualization. Many studies have been conducted related with prioritization of switchgear replacement. But it is difficult to interpret and apply to the power distribution system. That is because most of the studies just considers customer numbers for prioritizing the replacement. In this paper presents an algorithm to determine the intelligent swichgear replacement priority considering customer number, load quantity and interruption cost. Further, this algorithm is verified by using system reliability index.

• 정보처리학회논문지A
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• 제11A권2호
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• pp.175-180
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• 2004

DVD, MP3, AAC 등과 같은 고품질의 디지털콘텐트는 품질의 손상 없이 복제되어 인터넷을 통해 배포 가능하며, 이는 디지털콘텐트 제공자에게 커다란 경제적 손실을 주게 된다. 이에 따라 디지털콘텐트의 안전하고 효율적인 분배를 위한 연구가 필요하다. 디지털콘텐트 분배 시스템의 설계에서 가장 중요한 이슈는 사용자 편의성과 실행 속도, 보안성 문제라 할 수 있다. 본 연구는 웹 캐싱 기술과 계층구조의 암호화/복호화 기법을 사용한 웹 기반의 디지털콘텐트 분배 시스템을 설계하였다. 본 연구에서 제안한 시스템은 보안성과 실행속도, 사용자의 편의성을 향상시킨 디지털콘텐트 분배 시스템이며, 실험을 통해 성능의 우수성을 검증하였다.

• 대한전기학회논문지:전력기술부문A
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• 제51권1호
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• pp.15-22
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• 2002

This paper proposes a new power flow method for distribution system analysis by modifying the conventional back/forward sweep method using symmetrical components. Since the proposed method backward and forward sweeps with the variables expressed by symmetrical components, this method reduces computation time for matrix calculations; therefore, it is able to reduce the computational burden for real-time distribution network analysis. The proposed method was also developed to effectively analyze the unbalanced distribution system installing AVR(Auto Voltage Regulator), shunt capacitors. The proposed algorithm was compared with the conventional Back/forward Sweep method by applying both methods to three phase unbalanced distribution system of IEEE 123-bus model, and the test results showed that the proposed method would outperformed the conventional method in real-time distribution system analysis.

• 조명전기설비학회논문지
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• 제29권5호
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• pp.71-79
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• 2015

Recently, new Low Voltage DC (LVDC) power distribution systems have been constantly researched as uses of DC in end-user equipment are increased. As in conventional AC distribution system, High Impedance Fault (HIF) which may cause a failure of protective relay can occur in LVDC distribution system as well. It, however, is hard to be detected since change in magnitude of current due to the fault is too small to detect the fault by the protective relay using overcurrent element. In order to solve the problem, this paper presents an algorithm for detecting HIF using accumulated energy in LVDC distribution system. Wavelet Singular Value Decomposition (WSVD) is used to extract abnormal high frequency components from fault current and accumulated energy of high frequency components is considered as the element to detect the fault. LVDC distribution system including AC/DC and DC/DC converter is modeled to verify the proposed algorithm using ElectroMagnetic Transient Program (EMTP) software. Simulation results considering various conditions show that the proposed algorithm can be utilized to effectively detect HIF.

• 전기학회논문지
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• 제58권11호
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• pp.2107-2114
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• 2009

It is impossible to take the instant action in the distribution system When fault occures in a substation because operation of the substation and the distribution system are separated. However the power system automation has been studying about unity operation and co-operation between SCADA and DAS(Distribution Automation System). In this paper proposes a new algorithm of efficiency restoration using a outage load switching to a healthy MTR a fault occurrence at a MTR in united system between DAS and SCADA. In addtion, proposed algorithm includes a outage restoration method which keeps MTR optimal capacity with reorganization of distribution network in case it can not restore outage state loads caused by shortage of healthy MTR remain capacity. In case that proposed sequence still can not complete restoration, this paper suggests a efficiency outage restoration with objective function included priority in outage loads. In the case studies, the proposed algorithm have been verified in 2 MTR and 3 MTR substation

• KEPCO Journal on Electric Power and Energy
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• 제6권3호
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• pp.279-284
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• 2020

This paper presents the conceptual design of a cooperative control with Energy Management System (EMS) and Distribution Management System (DMS). This control enables insufficient reactive power reserve in a power transmission system to be supplemented by surplus reactive power in a power distribution system on the basis of the amount of the needed reactive power reserve calculated by the EMS. This can be achieved, because increased numbers of microgrids with distributed energy resources will be installed in the distribution system. Furthermore, the DMS with smart control strategy by using surplus reactive power in the distribution system of the area has been gradually installed in the system as well. Therefore, a kind of hierarchical voltage control and cooperative control scheme could be considered for the effective use of energy resources. A quantitative index to evaluate the current reactive power reserve of the transmission system is also required. In the paper, the algorithm for the whole cooperative control system, including Area-Q Indicator (AQI) as the index for the current reactive power reserve of a voltage control area, is devised and presented. Finally, the performance of the proposed system is proven by several simulation studies.

• 전기학회논문지P
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• 제62권4호
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• pp.210-215
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• 2013

This paper analyze the bus voltage sags in the power distribution system with a small scale cogeneration system when the superconducting fault current limiter was introduced. Among the solutions to decrease the short-circuit current considering the locations of the small scale cogeneration system, the superconducting fault current limiter (SFCL) has been announced as one of the promising methods to reduce the fault current because the installation of the small scale cogeneration system which increases the short-circuit current. According to the application locations of the small scale cogeneration system in a power distribution system, it has caused the variations of voltage sag and duration which depends on the change of the short-circuit current, which can make the operation of the protective device deviate from its original set value when the fault occurs. To investigate the voltage sag when a SFCL was applied into a power distribution system where the small scale cogeneration system was introduced into various locations, the SFCL, small scale cogeneration system, and power system are modeled using PSCAD/EMTDC. In this paper, the effects on voltage sags are assessed when the SFCL is installed in power distribution system with various locations of the small scale cogeneration system.

• Journal of Electrical Engineering and Technology
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• 제8권6호
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• pp.1305-1309
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• 2013

The application of the superconducting fault current limiter (SFCL) in a power distribution system is expected to contribute the voltage-sag suppression of the bus line as well as the fault-current reduction of the fault line. However, the application effects of the SFCL on the voltage sag of the bus line including the fault current are dependent on its application location in a power distribution system. In this paper, we investigated the fault current limiting and the voltage sag suppressing characteristics of the SFCL due to its application location such as the outgoing point of the feeder, the bus line, the neutral line and the 2nd side of the main transformer in a power distribution system, and analyzed the trace variations of the bus-voltage and fault-feeder current. The simulated power distribution system, which was composed of the universal power source, two transformers with the parallel connection and the impedance load banks connected with the 2nd side of the transformer through the power transmission lines, was constructed and the short-circuit tests for the constructed system were carried out. Through the analysis on the short-circuit tests for the simulated power distribution system with the SFCLs applied into its representative locations, the effects from the SFCL's application on the power distribution system were discussed from the viewpoints of both the suppression of the bus-voltage sag and the reduction of the fault current.

• 조명전기설비학회논문지
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• 제22권8호
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• pp.38-44
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• 2008

급격한 IT 산업 발전의 산물인 인터넷데이터센터(IDC)는 서버 시스템이 집적된 고밀도 디지털 부하로 구성되는 특징을 가지고 있다. IDC의 디지털 부하 특성을 고려하여 직류배전시스템을 도입하는 경우 전력 변환 체계의 단순화로 효율 향상의 가능성이 일부 제기되어 왔으나, 국내 IDC 환경에서의 효율성이 검증된 사례는 없었다. 본 논문에서는 교류배전방식을 적용한 KT 분당 IDC와 직류배전방식을 적용한 KT 남수원 IDC의 전력 효율을 비교 분석함으로써 국내 IDC 배전체계의 직류화에 따른 효율 개선 효과를 제시하였다. DC 48[V]를 배전하였을 때 직류배전 방식의 효율이 13.2[%] 높은 것으로 도출되었으며, DC 380[V]의 공급을 가정하였을 때에는 25[%] 이상의 효율 향상을 기대할 수 있었다.