Korean Distribution System Research Articles

Providing grid flexibility with sector coupling technologies in Korean distribution system

Recently, world-wide efforts are being made to cope with the global climate crisis. Among many countries, Korean government has set the goal of achieving carbon neutrality by 2050. To this end, as well as increase of renewable energy, system planning, implementation, and research on various measures such as microgrid construction, sector coupling, and Energy Superstation have continued. This paper introduces the methods and analyzes the effects of the Energy Superstation. Simulations are constructed using the charging pattern and electricity consumption pattern of electric vehicles, and the effects on the system are evaluated.

배전계통 전압 측정오차가 분산전원 출력 제어에 미치는 영향 분석

In this paper, effect of error in voltage measurement on output control of distributed generations(DGs) for voltage regulation in distribution systems is analyzed. Volt-Var and Volt-Watt control of a smart inverter which is regarded as one of the typical voltage regulation algorithms based on voltage measurement is considered and characteristics of active/reactive power control and performance of voltage regulation are theoretically evaluated. For verification of the analyzed effect, simulations based on the Korean distribution system are performed by using MATLAB/Simulink. Based on the simulation results, we can confirm that output control of DGs based on the voltage measurement at point of common coupling (PCC) is highly affected by even small error in voltage measurement.

Optimal Volt–Var Curve Setting of a Smart Inverter for Improving Its Performance in a Distribution System

We propose an algorithm to set the parameters of volt-var curves to improve the performance of distributed generation. Specifically, we optimally set the volt-var curves of the smart inverter for proper control of the distributed generation output. To improve the overall distribution system performance, we consider the minimization of voltage deviation, system loss, and peak of reactive power in an objective function, thereby providing optimal volt-var curve parameters. The proposed algorithm overcomes various limitations of existing studies. First, we use distribution system factors in a multiobjective optimization function to adjust volt-var curve parameters that deviate from the default settings. Second, we consider the service transformers that affect the system voltage according to the photovoltaic generation output in the test model during optimization. Third, we analyze the system improvement according to the number of parameters to be optimized. Fourth, we analyze the implementation of the optimized volt-var curve according to the practical periods when the smart inverter settings can be updated. Fifth, we evaluate different suitable volt-var curves for multiple photovoltaic generators grouped using clustering. Using the proposed algorithm, the distribution system operator can set the optimal volt-var curve according to the system conditions and requirements. We conducted simulations of the proposed method using OpenDSS, a quasistatic time-series simulation, on a test model reflecting the characteristics of a South Korean distribution system. The simulation results confirm that the overall system performance increases when the optimal volt-var curve settings obtained from the proposed algorithm are used.

Optimal Planning of Distributed Generators for Integration of Electric Vehicles in a Korean Distribution System

Due to the rising concerns about global warming, Korean government is encouraging the penetration of electrical vehicles (EVs). Integrating a large number of EVs may expose the distribution systems to high voltage drops and increased energy losses. In this paper, we have carried out the optimal planning of distributed generators (DGs) in a Korean distribution feeder to enhance the penetration of EVs. The optimization problem is formulated as a mix-integer non-linear programming for minimizing the energy losses in the distribution feeder. The real traffic volume of Seoul, Korea is used for modelling the power demand of EVs. Wind and dispatchable DGs are considered as the DG-types, and Weibull distribution is applied to model the probabilistic behavior of wind speed. In order to estimate the parameters of Weibull distribution from the wind speed data, maximum likelihood estimation method is employed. The optimization problem is solved using genetic algorithm. Moreover, four test cases are considered for the simulation on the distribution system to validate the performance of the proposed planning approach. The results show that the energy losses caused by the integration of EVs are reduced while the voltage profile of the distribution feeder is enhanced.

New Simulation Method of Flashover Rate by Connection of EMTP and MATLAB

Because of the random characteristics of lightning, the Monte Carlo method is applied to estimate the flashover rate due to lightning, however, the simulations using previous methods are difficult to both beginner and expert in power corporations. Therefore, this paper proposes the new and easy method to simulate the flashover rate by connection of electromagnetic transients program (EMTP) and MATLAB. The magnitude of a lightning strike is based on a curve measured in the field, while the classification of direct and indirect lightning depends on the striking distance. In a Korean distribution system, the flashover rate induced by lightning is simulated using proposed method. Simulations of the footing resistance according to the existence of an overhead ground wire (OHGW) are performed and the simulation results are discussed. The simulation results are compared with findings obtained with the IEEE Flash 2.0 program.

Applicability of Messenger Wire for Purpose of Lightning Protection

The Korean distribution line currently consists of overhead ground wires (OHGW), overhead distribution lines, neutral wires (NW), and messenger wires (MW). The MW is installed under the NW. The lightning protection system in Korea is focused on OHGW and lightning arrester and the MW are not considered. Therefore, this paper proposes the applicability of MW for purpose of lightning protection. For this, we analyzed the effects of lightning overvoltage according to the existence of OHGW and MW and the grounding conditions of the MW in the Korean distribution system. The grounding conditions of the MW that we took into consideration were the common or separate grounding of the MW and NW. The analysis based on the equivalent circuit of the distribution pole at each condition was performed. The distribution lines and lightning were modeled using the Electromagnetic Transients Program (EMTP). For each of the installation conditions of the OHGW and MW, the various lightning conditions were simulated and analyzed for both direct and indirect lightning. The simulation results showed that, if the OHGW was not installed in the Korean distribution system, the lightning overvoltage could be reduced by the common grounding of the MW and NW.

Transient State Analysis of Lightning Surge on Distribution Systems

This paper simulates the transient state of distribution system when a lightning surge strikes a distribution line. Because the Korean distribution system consists of mainly neutral wire, phase conductors and overhead ground wire, there is a high probability of lightning surge to distribution line. In this situation, surge arrester is usually installed to protect distribution system. In this paper, distribution line is modeled by using EMTP (Electromagnetic Transients Program) and the optimal interval of lightning arresters and the optimal size of grounding resistance for stable system according to the wave front time of lightning surge are determined.

Short Circuit Withstanding Capability of 22.9kV HTS Cable in Korea

AbstractIn Korea, GENI(Green superconducting Electric power Network at the Icheon substation) project has been conducted since 2008. The objective of the GENI project is to install and operate a 22.9kV/50MVA High Temperature Superconducting (HTS) cable system and a 22.9kV/630A Superconducting Fault Current Limiter (SFCL) system in the Icheon substation located near Seoul. It is important to design specifications considering real power system conditions for a successful application of the HTS cable and SFCL system to a real grid. This paper proposes a design specification for the short circuit withstanding capability of the HTS cable to apply to Korean power distribution system, from the viewpoint of a protection system. The HTS cable system with the proposed specification has been operated in the Korean real grid of the Icheon substation since August, 2011.

국내 배전계통의 가공지선 접지조건에 따른 뇌서지 영향 분석

The Korean distribution system consists of overhead ground wire (OHGW), phase conductors and neutral wire. Especially, OHGW is installed over the phase conductors to protect distribution system from the lightning surge. The flashover rate and the magnitude of lightning overvoltage on distribution system can be affected by grounding condition of OHGW such as grounding resistance and grounding interval. In this paper, we conduct an analysis of lightning overvoltage and flashover rate according to the grounding condition of OHGW. The distribution system and lightning surge are modeled by using ElectroMagnetic Transient Program (EMTP). Also, the Monte Carlo method is applied to consider random characteristics of lightning, and the flashover rate is calculated based on IEEE std. 1410. The simulations are performed by changing the grounding resistance and interval of OHGW and the simulation results are analyzed.

Specifications of the 22.9 kV SFCL Considering Protection Systems in Korean Power Distribution System

The GENI project for applying the 22.9 kV HTS cable and the SFCL to real power system has been progressed in South Korea since 2008. The HTS power devices were applied to the Icheon substation in the real Korean power grid in August 2011. This is the first demonstration of HTS power devices in South Korea. For a successful application, this paper proposes proper specifications of a current limiting resistor/reactor and an activating current for the 22.9 kV SFCL in the Korean power distribution system. These specifications are determined, considering the protection system of real Korean power system.

An Amendment of the VLF tanδ Criteria to Improve the Diagnostic Accuracy of the XLPE-insulated Power Cables

VLF diagnosis technology is introduced in IEEE Std 400 and proposed as evaluation criterion in an effective way of detecting water tree which mainly causes the failure of XLPE insulated cables. In order to inspect the accuracy of the VLF method for XLPE insulated power cables in Korean distribution system, diagnosis for 41 cables which were being serviced in the fields has been carried out and they were removed for AC breakdown voltage test after. Regarding the 41 cables, it was hard to confirm any relation between the VLF values and AC breakdown voltages and also water tree in the insulation was not detected. However, the other cables were failed several days after the diagnosis of the 41 cables. Water trees were found and their VLF values were also much higher than the criterion of IEEE standard. It has been ascertained that we need to change the IEEE criteria in order to improve the accuracy of detecting water trees by additional analyzing of field examples of failure and case studies from overseas countries and therefore amended VLF test voltage and evaluation criteria have been proposed.

Ungrounded System Fault Section Detection Method by Comparison of Phase Angle of Zero-Sequence Current

In this paper, an integrated fault section detection and isolation strategy is proposed based on the application of the Distribution Automation System(DAS) utilizing advanced IT and communication technologies. The Feeder Remote Terminal Unit(FRTU) has been widely used to collect data in the Korean distribution system. The achieved data is adopted in this method for detecting multiple fault types. Especially in the case of single phase-to-ground fault, the fault section is detected by comparison of the zero-sequence current phase angle. The test results have verified the effectiveness of the proposed method in a radial distribution system through extensive simulations in Matlab/Simulink. Furthermore, a communication-based demo system identical to the simulation model has been developed, and it can be applied as an online monitoring and control program for fault section detection and isolation.

The Korean Distribution System

As South Korea (hereafter, Korea) emerges as one of the largest markets for U.S.- and European-made goods, a growing number of U.S. and European firms have expressed keen interest in penetrating the lucrative Korean market. Despite the enthusiasm of U.S. and European firms, they are faced with an array of invisible market barriers that makes it difficult for them to sell their products in Korea. The Korean distribution system is often symbolic of such barriers. In general, the Korean distribution system is characterized as closed and multifarious with the co-existence of manufacturer-controlled distributors and an excessively large number of small-scale “mom-and-pop” retail stores. Due to its unique structure, the Korean distribution system has been generally misunderstood by many Westerners and subsequently this misunderstanding has created an unnecessary strain on trade relations with Korea. In this paper, we provide an overview of the Korean distribution system and then formulate proactive distribution/marketing strategies for the successful penetration of the Korean market.

Supply chain integration in developing countries for foreign retailers in Korea: Wal-Mart experience

Wal-Mart entered into the Korean market in 1997 after regulations governing foreign retailers were completely lifted. Since Wal-Mart began its retailing operations in Korea, it made every effort to incorporate the principles of supply chain integration in Korea. Currently, many supply chain integration attempts made in Korea have made some contributions to the development of the Korean distribution system, even though the results are not completely satisfactory. Two reasons might be cited. First, there is no noticeable competitive supply chain infrastructure in Korea to support the principles of supply chain integration. Highly competitive and aggressive supply chain strategies that Wal-Mart has been accustomed to using in the United States are directly in conflict with the existing distribution channels in Korea. Second, a relationship building process among supply chain partners (internal as well as external) has been painfully slow at best and in many instances non-existent. However, there is an opportunity in Korea for many foreign retailers to reduce the supply chain cost if it is properly implemented. This paper closely examines some of the reasons why the supply chain integration process for foreign retailers in Korea has been slow, and the attempts to provide possible solutions.

Implications of the Restructured Logistics Systems in South Korea — How to Succeed

The tremendous economic changes occurring in Korea have created trends of high quality products, mass consumption, an emergence of the younger generation, and competition among firms. This competition also includes foreign firms in the Korean distribution system. To respond to these diversifying consumer behaviors, the Korean government has opened its market to foreign firms and restructured its distribution system. As the Korean distribution system changes, it raises questions for foreign firms; how to penetrate the restructured distribution system and how to succeed in the Korean market.