• Korean Journal of Materials Research
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• v.33 no.1
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• pp.21-28
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• 2023

The electromembrane process, which has advantages such as scalability, sustainability, and eco-friendliness, is used in renewable energy fields such as fuel cells and reverse electrodialysis power generation. Most of the research to visualize the internal flow in the electromembrane process has mainly been conducted on heterogeneous ion exchange membranes, because of the non-uniform swelling characteristics of the homogeneous membrane. In this study, we successfully visualize the electro-convective vortices near the Nafion homogeneous membrane in PDMS-based microfluidic devices. To reinforce the mechanical rigidity and minimize the non-uniform swelling characteristics of the homogeneous membrane, a newly developed swelling supporter was additionally adapted to the Nafion membrane. Thus, a clear image of electroconvective vortices near the Nafion membrane could be obtained and visualized. As a result, we observed that the heterogeneous membrane has relatively stronger electroconvective vortices compared to the Nafion homogeneous membranes. Regarding electrical response, the Nafion membrane has a higher limiting current and less overlimiting current compared to the heterogeneous membrane. Based on our visualization, it is assumed that the heterogeneous membrane has more activated electroconvective vortices, which lower electrical resistance in the overlimiting current regime. We anticipate that this work can contribute to the fundamental understanding of the ion transport characteristics depending on the homogeneity of ion exchange membranes.

• Journal of the Korea Convergence Society
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• v.2 no.4
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• pp.29-37
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• 2011

Dispersed generation (DG) such as wind power (WP) and Photovoltaic systems (PV) that has been promoted at the national level recently is mainly being introduced into distribution systems adjacent to consumers because it is generation on a small scale when compared to current generation. Due to its characteristics, DG can be operated by interconnection with distribution systems to present security of more stable power and efficient use of power facilities and resources. Problems on protection coordination of distribution systems by reverse flow of DG can roughly be divided into three possibilities: excess in rated breaking capacity (12.5KA) of protective devices by a fault in DG current supply, failure to operate protective devices by an apparent effect that can occur by reduction in impedance parallel circuit fault current due to interconnection of DG, and malfunction of protective devices by interconnection transformer connection type. The purpose of this study is to analyze problems in protection coordination that can occur when DG is operated by interconnection with distribution systems by conducting modeling and simulations by using theoretical symmetrical components and MATLAB/SIMULINK to present methods to improve such problems.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.11
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• pp.239-249
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• 2019

Recently, the Korean government has implemented a policy to expand renewable energy sources. Large-scale PV systems are being actively interconnected with the distribution system. On the other hand, when a large-scale PV system is installed and operated, the customer voltages could violate the allowable voltage limit due to reverse power flow of the PV system. To overcome these problems, an enhancement method for hosting the capacity of the PV system in a distribution system is being actively conducted. Therefore, to improve the hosting capacity of the PV system, this paper proposes a model of a reconfiguration of the distribution system, which is composed of three sections and three connections based on PSCAD/EMTDC S/W, and proposes an evaluation algorithm for the feeder reconfiguration to maximize an adaption of the PV system. In addition, this paper presents the optimal method of the feeder reconfiguration section to evaluate the maximum capacity of the PV system to keep customer voltages within the allowable voltage limits based on various operation scenarios, such as the capacity of a PV system and section of feeder reconfiguration. From the simulation results based on the PSCAD/EMTDC modeling and evaluation algorithm, it was confirmed that they are a useful and practical tool to enhance hosting the capacity of a PV system in a distribution system.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.6
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• pp.9-20
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• 2018

When a large-scale photovoltaic (PV) system is introduced into a distribution system, the customer's voltage may exceed the allowable limit ($220V{\pm}6%$) due to voltage variations and reverse power flow in the PV system. In order to solve this problem, we propose a method for adjusting the customer voltage using the existing step voltage regulator (SVR) installed in the primary feeder. However, due to the characteristics of a mechanically operating SVR, the customer voltage during the tap changing time of the SVR is likely to deviate from the allowable limit. In this paper, an energy storage system (ESS) with optimal operation strategies, and an appropriate capacity calculation algorithm are proposed, and the parallel driving scheme between the SVR and the ESS is also proposed to solve the customer voltage problem that may occur during the tap changing time of the SVR. The simulation results show that the allowable limit of the customer voltage is verified by the proposed methods during the tap changing time of the SVR when the large-scale PV system is connected to the distribution system.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.5
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• pp.22-33
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• 2021

In the case of open phase faults caused by the disconnection of distribution feeders interconnected to a PV system, many problems can occur depending on the core type and wiring method of the grid-connected transformers. Moreover, open phase faults are difficult to detect because the open phase voltage of the existing protection relay (Open Phase Relay (47)) can be maintained, even though a disconnection fault occurred, depending on the wiring method and the iron core type of the grid-connected transformer for a PV system. Therefore, this paper proposes a novel algorithm to detect open phase faults by comparing the currents and phases between the primary and secondary sides of a grid-connected transformer. In addition, this paper presents the modeling of a distribution system and protection devices for detecting open phase faults using PSCAD/EMTDC S/W, and implements a test protection device for detecting open phase faults based on the above-mentioned modeling. The simulation and test results confirmed that the proposed algorithm is useful for detecting open phase faults according to the wiring method and iron core type of grid-connected transformer for a PV system because operation slope and unbalance rate of the primary current exceed the setting value (30[%]) of the protection device.