• The Transactions of the Korean Institute of Electrical Engineers A
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• v.54 no.11
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• pp.548-556
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• 2005

Reliability evaluation of power distribution system is very important to both power utilities and customers. It present the probabilistic number and duration of interruption such as failure rate, SATDI, SAIFI, and CAIDI. However, it has a fatal weakness at reliability index because of accuracy of failure rate. In this paper, the Time-varying Failure Rate(TFR) of power distribution system equipment is extracted from the recorded failure data of KEPCO(Korea Electric Power Corporation) in Korea. For TFR extraction, it is used that the fault data accumulated by KEPCO during 10 years. The TFR is approximated to bathtub curve using the exponential(random failure) and Weibull(aging failure) distribution function. In addition, Kaplan-Meier estimation is applied to TFR extraction because of incomplete failure data of KEPCO. Finally, Probability plot and regression analysis is applied. It is presented that the extracted TFR is more effective and useful than Mean Failure Rate(MfR) through the comparison between TFR and MFR

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.53 no.5
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• pp.266-274
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• 2004

This paper presents a scheme for the interconnection of dispersed generator systems(DGs) based on load .unbalance and load model in composite distribution systems. Groups of each individual load model consist of residential, industrial, commercial, official and agricultural load. The unbalance is involved with many single-phase line segment. . Voltage profile improvement and system loss minimization by installation of DGs depend greatly on how they are placed and operated in the distribution systems. So, DGs can reduce distribution real power losses and replace large-scale generators if they are placed appropriately in the distribution systems. The main idea of solving fuzzy goal programming is to transform the original objective function and constraints into the equivalent multi-objectives functions with fuzzy sets to evaluate their imprecise nature for the criterion of power loss minimization, the number or total capacity of DGs and the bus voltage deviation, and then solve the problem using genetic algorithm. The method proposed is applied to IEEE 13 bus and 34 bus test systems to demonstrate its effectiveness.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.49 no.4
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• pp.177-184
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• 2000

In this paper, we proposes a method for assessing the effect of voltage sag in power distribution systems using fuzzy model. The proposed method is based on the reliability data of distribution system and specified computer business equipment manufacturer association(SCBEMA) curve that express the representative power acceptability curve by voltage sag for each customer type. The SCBEMA curves are made by using the CBEMA curves obtained from the experiment for the customers sensitive equipment. In order to transform SCBEMA curves to the differential damage by voltage sag, a fuzzy model is used. The proposed fuzzy model is composed to reflect two parameters of customers damage by voltage sag. One is the duration and magnitude of voltage sag and the other is the different risk due to the customer types. The Monte Carlo simulation method and the historical reliability data in KEPCO ae used for case studies.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.52 no.12
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• pp.705-712
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• 2003

In this paper, we propose new unified methodologies of reliability and its cost evaluation in power distribution systems. The unified method means that the proposed reliability approaches consider both conventional evaluation factor, i.e. sustained interruptions and additional ones, i.e. momentary interruptions and voltage sags. Because the three voltage quality phenomena generally originate from the outages on distribution systems, the basic and additional reliability indices are summarized considering the fault clearing mechanism. The proposed unified method is divided into the reliability evaluation for calculating the reliability indices and reliability cost evaluation for assessing the damage of customer. The analytic and probabilistic methodologies are presented for each unified reliability and its cost evaluation. The time sequential Monte Carlo technique is used for the probabilistic method. The proposed DVL(Demand Varying Load) model is added to the reliability cost evaluation substituting the average load model. The proposed methods are tested using the modified RBTS(Roy Billinton Test System) form and historical reliability data of KEPCO(Korea Electric Power Corporation) system. The daily load profile of the each customer type in domestic are gathered for the DVL model. Through the case studies, it is verified that the proposed methods can be effectively applied to the distribution systems for more detail reliability assessment than conventional approaches.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2003.10a
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• pp.49-52
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• 2003

As the power demand has increased, it is expected that the transmission system will have more complicated problems under the influence of investment reduction for overall power system. The route length per MW demand will be reduced gradually from 0.6［C-km/㎿］ to 0.53 ［C-km/㎿］ in 2010. This comes up to a real serious problem of system planning and operation viewpoints HTS power technologies have properties to solve these complex transmission and distribution constraints, especially for metropolitan area, in the future. As the HTS technology has developed, the HTS cable technology can be the most effective alternative to solve the future expected transmission constraints as compared with other countermeasures in terms of economics, environments and system operation. This paper describes the general application methodology of developing 22.9 ㎸ HTS cable by CAST for practical distribution system, particularly, step-by-step application methodology of 22.9 ㎸ HTS cable to substitute the existing and planning 154 ㎸ cable. In this scheme, almost of the downtown 154 ㎸ substation of metropolitan city such as Seoul will be changed into 22,9 ㎸ switching station.

• Proceedings of the KIEE Conference
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• 2003.07a
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• pp.342-344
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• 2003

This paper describes the correction of overcurrent protective relaying set value in distribution networks interconnected with wind farm by dedicated line. The wind farm composed of wind turbine generators is one of the great energy sources; however, it would be also highly possible that the current in the point of common coupling is influenced by the output power of wind farm. So, the overcurrent relay applied in distribution feeders might generate trip signal for normal operation. In order to prevent the mal-operation of overcurrent relay, it is necessary to correct the relay's setting value according to the output power of end farm. This paper presents the influence of wind farm on the overcurrent relaying set value in distribution feeders for cases of fault as well as normal operation and proposes the basic strategy for correction of overcurrent relaying set value.

• Proceedings of the KSR Conference
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• 2005.11a
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• pp.736-741
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• 2005

This paper presents electric characteristics analysis and safe configuration for extension power supply between existent 6.6kV ungrounded distribution system and establishment and improvement 22.9kV direct grounding distribution system. For this, we model 6.6kV ungrounded and 22.9kV direct grounding distribution system of urban underground, ground region. and rural electrical, unelectrical region using PSCAD/EMTDC and analyze voltage drop, charging current, ground and short fault through simulation. To analyze electric characteristics of extension power supply, we simulate extension power supply of overhead line of 6.6kV ungrounded system and underground line of 22.9kV direct grounding system of rural electrical region and propose operation condition for safe extension power supply through result of analysis. Characteristics of voltage drop, charging current, ground and short fault appear almost similarly with electrical characteristic of direct power supply. However, because unbalance of phases may cause relay's malfunction of ungrounded system and ground fault current of direct grounding system may demage facilities of ungrounded system, we propose safe system configuration such as impedance grounding system of neutral point.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.55 no.4
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• pp.139-143
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• 2006

Recently, standard of living improved and Information-Communication industry developed rapidly. Thereby, interest about electric power quality is rising worldwide. So, research and Development to enhance electric power quality in various viewpoint until most suitable supply system from each kind device to improve electric power quality. And specially, interest about voltage quality is rising by diffusion increase of information communication appliance and minuteness control appliance etc. Also Power consumption is increasing, but expansion of large size generator by environmental and site security problem is difficult. So, introduction of distribution generation is investigated actively by electric-power industry reorganization. Voltage management of power system had been controlled by ULTC (Under Load Tap Changer) in substation and pole transformer on the high voltage distribution line. But, voltage control device on substation and distribution line is applied each other separatively. Therefore, efficiency of line voltage control equipment is dropping. Also, research about introduction upper limit of distribution generation is consisting continuously. This paper presents cooperation use way between voltage control device and introduction upper limit of distribution generation for most suitable voltage control in distribution power system.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.48 no.11
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• pp.1388-1393
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• 1999

A more reliable algorithm for detecting a high impedance fault (HIF) requires fault currents at the relaying point containing information of load condition as well as HIF characteristics. This paper presents a modeling method of an HIF in a distribution system using EMTP. From the voltage and current waveforms of HIF experiment, the voltage-current characteristic is obtained and then piecewise linearized. The proposed method gets several points on the linearized voltage-current curve and then represents nonlinearity as piecewise linear resistances using Transient Analysis of Control Systems (TACS) in EMTP. Thus, an HIF is represented as a voltage source in the first and third quadrants of voltage-current plane. The method is implemented in EMTP and thus the voltage and current at the relaying point can be obtained when an HIF occurs. In this paper, an HIF was simulated on various load conditions and fault conditions in 22.9 [kV] distribution systems.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.3
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• pp.465-470
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• 2011

Recently fault currents are increasing in a network. It is caused by increase in electric demand and high penetration of distributed generation with renewable energy sources. Moreover, distribution network has become more and more complex as mesh network to improve the distribution system reliability and increase the flexibility and agility of network operation. Accordingly, the fault current will exceed capacity of circuit breakers soon and all the various rational solutions to solve this problem are taken into account. Under these circumstances, superconducting fault current limiter(SFCL) is a new alternative in the viewpoint of technical and economic aspects. This study presents operation processes for a resistive-type of SFCL, and it proposes reliability model for the SFCL. When a SFCL is installed into a network, the contribution of decreased fault currents to failure for distribution equipments can be quantified. As a result, it is expected that a SFCL makes the reliability of adjacent equipments on existing network improve and these changes are analyzed. We propose a methodology to evaluate the reliability in the distribution network where a SFCL is installed considering a reliability model for resistive-type of SFCL and reliability changes for adjacent equipments which are proposed in this paper.