https://doi.org/10.5370/KIEE.2024.73.11.1873

김준혁(Jun-Hyeok Kim)

In distribution systems, load transfers cause sudden fluctuations, necessitating rapid detection to ensure effective operations and infrastructure management. These fluctuations can compromise grid stability, and if undetected, lead to inefficiencies. Also, the growing integration of solar power has heightened the importance of identifying load transfers, especially due to reverse power flow issues. Traditional detection methods are often complex and data-intensive, limiting their practical application. This study introduces a novel method using time series decomposition, moving averages, and moving standard deviations to efficiently detect load transfers. The approach is simple, data-efficient, and offers real-time detection capabilities. Validation against real-world planned load transfers demonstrated high accuracy and reliability, proving its effectiveness in supporting grid stability and infrastructure management.

https://doi.org/10.5370/KIEE.2024.73.11.1878

곽효근(Hyo-Geun Kwak) ; 이효(Hyo Lee) ; 남태식(Taesik Nam) ; 강지성(Ji-Seong Kang) ; 심재웅(Jae Woong Shim)

This paper presents the method of avoiding resonance and reducing voltage harmonics by connecting a C-type filter to the capacitor section of an LCL filter which connected to the inverter. For this purpose, we set the parameters of the inverter and LCL filter. Then, various equations were employed to appropriately determine the values of the capacitor, inductor, and resistor of the C-type filter. Utilizing these configured values, the overall transfer function was represented using the transfer functions of the controller and filter. Subsequently, it was examined whether unstable resonance could be avoided when using the C-type filter. Furthermore, in the frequency domain, the Total Harmonic Distortion(THD) was utilized to assess how much the voltage harmonics decreased when the C-type filter was included, compared to when only the LCL filter was present.

https://doi.org/10.5370/KIEE.2024.73.11.1888

박준수(Junsu Park) ; 문승필(Seungpil Moon) ; 윤민한(Minhan Yoon)

As the penetration ratio of renewable energy known as inverter based resources(IBR) to power system increases worldwide, large amount of IBR causes various problems. Most of the IBR currently used in the Korean power system are Grid Following Inverter(GFLI) and have an output issue due to unstable phase angle when the grid disturbance occurs. In addition, there is a limit of instantaneous inertial output due to basic controller structure and delay of Phase Locked Loop(PLL). Under these circumstances, Grid Forming Inverter(GFMI), which self-controls voltage and phase angle like a synchronous machine, is attracting attention as a alternatives that can contribute to increasing system stability and inertial energy. In this paper, GFMI with various power control was constructed in PSS/e User Defined Model(UDM), and the output characteristics of the GFMI in the test system were verified through System Frequency Response(SFR) and Per Unit(PU) based controller configuration. Then, the GFMI model was integrated into the Jeju system in Korea and the output characteristics in case of disturbances were compared in PSS/e simulation. When compared to existing GFLI, it was confirmed that the GFMI contributed to more initial inertial energy and injected stable reactive power for voltage control. Therefore, the need to increase the robustness and stability of the Jeju system through the GFMI ESS control mode was verified.

https://doi.org/10.5370/KIEE.2024.73.11.1898

윤민호(Min-Ho Yoon) ; 박찬묵(Chan-Muk Park) ; 김경탁(Kyoung-Tak Kim) ; 임성훈(Sung-Hun Lim)

Generally, a serial AC arc in multi-load configuration is difficult to detect because the line current contains multiple harmonic components corresponding to its compositive load characteristics. In this paper, serial AC arc algorithm using difference for fast fourier transform (FFT) variations of main line current was suggested and its effectiveness by applying into multi-load configuration was analyzed. Based on serial AC arc tests for multi-load configurations with different loads, the difference for FFT variations of main line current in each multi-load configuration was analyzed. The suggested algorithm was confirmed to detect the serial AC arc and was satisfied to be operated within the regulatory arc circuit breaker’s operation time for all multi-load configurations.

https://doi.org/10.5370/KIEE.2024.73.11.1904

정주용(JooYong Jung) ; 권영진(YoungJin Kwon) ; 김남규(NamKyu Kim)

To mitigate the instability of power systems caused by the increasing penetration of renewable energy sources, the installation of Static Synchronous Compensator(STATCOM), which serve as reactive power compensation devices, is on the rise. These devices, composed of converters with switching elements, generate harmonics, which can lead to harmonic interaction issues with nearby power electronics based equipment. Therefore, a detailed analysis of harmonic interaction is required when designing and operating STATCOM systems. In this paper, impedance modeling of the power system and STATCOM is implemented using Matlab software, and the possibility of resonance occurrence due to changes in controller parameters when integrating STATCOM into the power system is analyzed.

https://doi.org/10.5370/KIEE.2024.73.11.1910

문승필(Seungpil Moon) ; 방형필(Hyeongpil Bang) ; 최장흠(Jang-Heum Choi) ; 이연찬(Yeonchan Lee)

The purpose of this study is the fault discrimination of the transformer that supplies power in demand. In this study, the correlation between the light transmittance of the insulating oil and dielectric breakdown was used to the fault discrimination of the transformer. In this study, the light sources of various wavelengths were compared, and it was shown in the paper that the selected 520 nm light sources can clearly diagnose the deterioration state. In addition, in order to evaluate the total dielectric breakdown of the insulating oil, research was conducted through various samples through the collection of insulating oil samples and acceleration deterioration tests of the used transformer. It is believed that the diagnostic method for the state of the transformer using the light transmittance of the insulating oil proposed through this study can help secure the reliability and economy of the power facility.

https://doi.org/10.5370/KIEE.2024.73.11.1917

박준성(Jun-Sung Park) ; 최승수(Seung-Su Choi) ; 윤민호(Min-Ho Yoon) ; 임성훈(Sung-Hun Lim)

Generally, in case that the induction motor in power distributed system was driven, larger driving current due to starting operation of induction motor happened, which leads to drop of bus voltage and affects protective relays such as under voltage relay and over current relay. In this paper, to suppress the voltage drop and limit the driving current in power distributed system connected with induction motor, the countermeasure using superconducting fault current limiter (SFCL) was investigated. Among various SFCLs, three-phase autotransformer type SFCL, which was connected with three single-phase autotransformers through symmetrical arrangement of three dual iron-cores, was selected because it had advantage easily to adjust the operational current of SFCL by setting tap. Through the driving tests of induction motor and three-phase ground faults tests in simulated power distribution system, the driving current and fault current limiting operations of three-phase autotransformer type SFCL were analyzed to be performed effectively.

https://doi.org/10.5370/KIEE.2024.73.11.1924

박찬묵(Chan-Muk Park) ; 김수현(Su-Hyeon Kim) ; 임성훈(Sung-Hun Lim)

This paper suggests DC superconducting current limiting (SCL) circuit breaker (CB) that consists of two mechanical switchs (SWs), adjustable current limiting reactor (CLR) and two superconducting (SC) elements. The suggested DC SCL-CB can have advantage to perform DC fault current limiting and interrupting operation and two SWs’ sequential opening operation comprising DC SCL-CB by control circuit can protect two SC elements from DC fault current as well. Through DC short-circuit tests, SW1 was confirmed to alleviates the power burden on SC1 element and lower turn ratio of adjustable CLR was analyzed to be contributed to fast interrupting operation of SW2 by quench of SC2 element.

https://doi.org/10.5370/KIEE.2024.73.11.1930

최승수(Seung-Su Choi) ; 박민기(Min-Ki Park) ; 김수현(Su-Hyeon Kim) ; 김학군(Hak-Goon Kim) ; 임성훈(Sung-Hun Lim)

The application of distributed generations (DGs) is increasing. Because renewable energy is eco-friendly and has low carbon emissions interest on renewable energy based DGs is growing. However, as the number of DGs increases, the fault current magnitude in the system can either increase or decrease during faults. These changes can result in malfunctions or failure of overcurrent relays (OCRs), potentially leading to a large blackout. Research on superconducting fault current limiter (SFCL) to limit fault currents has been conducted, but applying SFCLs in distribution systems with DGs can complicate protective coordination among relays. In this paper, cases of malfunction and failure of OCRs due to the connection of distributed power sources were analyzed, and method to improve the protective coordination of OCRs using SFCLs were proposed.

https://doi.org/10.5370/KIEE.2024.73.11.1939

이경민(Kyung-Min Lee) ; 권대윤(Dae-Yun Kwon) ; 박철원(Chul-Won Park)

For precise monitoring and diagnosis of power grids, WAMS based on PMU is gradually being expanded and applied. KEPCO installed 35 PMUs at Yeonggwang substation as part of its efforts to build and utilize a next-generation intelligent transmission μ grid operation system. However, a large amount of PMU data can be damaged due to various causes such as communication μ failure, disturbance, and synchronization instability. In this paper, we propose an identification and correction algorithm of bad data, such as event duplicate and spike, for reliable and high-precision analysis of the RESs-linked substation. First, we outline a high-precision WAMS of the substation, which is connected to RESs. Second, we propose a PMU bad data identification using μ slope and count targeting 35 PMUs installed in a 154kV substation. A correction technique using μ average-based is presented and evaluated. Finally, the simulation results using 11 days of PMU Raw data collected from the substation showed that the proposed μ algorithm is satisfactory.

https://doi.org/10.5370/KIEE.2024.73.11.1945

이나경(Na-Kyung Lee) ; 최성문(Sung-Moon Choi) ; 김경화(Kyung-Hwa Kim) ; 유현상(Hyun-Sang You) ; 노대석(Dae-Seok Rho)

Recently, while the installations of renewable energy sources and MG system to solve global environment issues are actively being performed, demonstration projects on community MG system to secure self-energy supply rate are being carried out in Jeollanam-do province in Korea. Where, the community MG system can be operated as a type of grid-connected or off-grid MG systems depending on the self-energy supply rate, and the power outage region may be expanded in the 3-phase short circuit or single line ground fault if proper time intervals of protection coordination between forward and backup protection devices is not secured. Therefore, this paper proposes operation method of protection coordination to secure the minimum time intervals of protection coordination not only between protection devices(CB, recloser) in primary feeder and MG customer relay in the grid-connected MG system, but also between MG customer relay in CVCF inverter(diesel generator) and other MG customer relay in the off-grid MG system. Furthermore, this paper performs the modeling of grid-connected and off-grid community MG systems, which is composed of distribution system, ESS, PV system and geothermal generator, using PSCAD/EMTDC S/W in order to analyze the fault current characteristics in the case of 3-phase short circuit and single line ground faults. From the simulation results based on the fault current characteristics and Off-DAS S/W of protection coordination analysis program, it is confirmed that the proposed operation method is useful tool to operate community MG system because the time intervals of protection coordination between forward and backup protection devices are properly secured in all contingency scenarios.

https://doi.org/10.5370/KIEE.2024.73.11.1958

문석환(Seok-Hwan Moon) ; 박상수(Sang-Soo Park) ; 김상용(Sang-Yong Kim) ; 김진욱(Jin-Uk Kim) ; 황준하(Jun-Ha Hwang) ; 권진수(Jin-Su Gwon)

This paper proposes the design process of an inverter for 100kW-class military vehicle applying SiC-MOSFET. The SIC-MOSFET was selected in consideration of the performance and ease of design of the SIC-MOSFET, and the gate driver, DC-link capacitor, and heat sink were designed in consideration of the fast switching characteristics of the SIC-MOSFET and EMI noise. The designed SIC-MOSFET inverter was verified performance of the switching device through Double Pulse Test experiments and the performance of the inverter was verified by dynamo experiments.

https://doi.org/10.5370/KIEE.2024.73.11.1967

최현영(Hyeon Yeong Choi)

The electronic interlocking system controls train routes to ensure the safe operation of trains. This system analyzes and regulates the interdependent sequential locking conditions of the elements constituting a train route to prevent overlaps, conflicts, or unsafe conditions with other train routes. Additionally, it is used to control field signaling equipment during frequent shunting or maintenance operations within station yards. This paper examines the architecture and operational method of the electronic interlocking system and proposes a method to remotely manage control inputs while maintaining system reliability. The proposed method enables operators to transmit control inputs to the electronic interlocking system from a remote location and to monitor the status of on-site signaling equipment in real time. This method utilizes wireless communication to transmit control commands, incorporating security measures to ensure data integrity and confidentiality. To verify the proposed method, a remote control device for the electronic interlocking system was developed, and simulations and field tests were conducted. The test results demonstrate that the railway signaling equipment (e.g., switch) can be remotely controlled in a secure and efficient manner.

https://doi.org/10.5370/KIEE.2024.73.11.1975

김철민(Chul-Min Kim) ; 정택근(Taek-Keun Jung) ; 김종수(Jong-Soo Kim)

This paper studies a method for generating gate drive signals to achieve synchronous rectification (SR) operation in a high-frequency switching LLC resonant converter using Gallium Nitride (GaN)-based power semiconductors. Through simulation, we compared the operation of four different approximation-based methods for generating synchronous rectifier drive signals, without the need for additional sensing circuits, across different operating frequency ranges. We identified operational zones that could lead to system failure, such as Early Turn-On and Late Turn-Off, and proposed suitable system specifications for each driving method. Experiments were conducted on a 1kW LLC resonant converter to test two methods capable of stable operation even below the resonant frequency. Among these, the method where "the product of output voltage and duty ratio remains constant," which compensates SR duty considering O-mode region oscillation, demonstrated superior overall performance compared to other methods, achieving a peak efficiency of 98.25%.

https://doi.org/10.5370/KIEE.2024.73.11.1983

허인회(In-Hoi Heo) ; 표판식(Pan-Sik Pyo) ; 박성희(Sung-Hee Park) ; 박재준(Jae-Jun Park)

In order to apply bio-epoxy resin as an insulating material for eco-friendly high-voltage heavy electric equipment, petrochemical epoxy resin (bisphenol A type diglycidyl ether (DGEBA)) and epoxidized soybean oil (ESBO), which epoxidizes the double bonds of fatty acids, were used. Ten types of samples mixed based on stoichiometry were prepared. And to apply to heavy electric equipment for distribution, DGEBA:ESBO Mixture Contents Ratio (100:0, 90:10, 80:20, 70:30, 60:40, 50:50, 40:60, 30:70, 20: 80, 10phr:90phr) and Micro Silica (M10_65wt%) were mixed to produce 10 types of epoxy/micro silica composites. The content ratio of bioepoxy that can be used in heavy electrical equipment and the thermal temperature characteristics of the mixture according to temperature changes were analyzed and reviewed through three evaluations, DSC, DMA, and TMA measurements. In general, the possibility was confirmed in the petrochemical epoxy DGEBA:ESBO/Micro silica_65wt% composite with a DGEBA:ESBO content ratio of 70phr:30phr.

https://doi.org/10.5370/KIEE.2024.73.11.1996

김성주(Sung-Ju Kim) ; 곽창섭(Chang-Seob Kwak) ; 성민제(Min-Je Sung) ; 백명기(Myung Ki Baek)

In this study, a simulation-based digital twin model is presented through a reduced temperature control test device test. The simulation of the test device is performed with Fluent from Ansys, a commercial FVM (Finite Volume Method) software. This model consists of RS ROM (Response Surface ROM) that predicts the scalar value HeatEnergy, and Static ROM that predicts the velocity and temperature fields. The experimental verification compares the temperature sensor value with the predicted value of the Static ROM in the design value (DP, Desgin Point) 3. As a result, an average error of about -1.364 [C] occurs.

https://doi.org/10.5370/KIEE.2024.73.11.2004

황유민(Yu Min Hwang) ; 박상준(Sangjun Park) ; 이현용(Hyunyoung Lee) ; 고석갑(Seok-Kap Ko)

In this paper, we propose a novel deep learning model based on Koopman theory to learn the partial differential equations (PDEs) inherent in data observed from nonlinear dynamical systems for missing data imputation. Since nonlinear PDEs such as the Navier-Stokes equations in fields like fluid dynamics and quantum mechanics still lack solutions, this paper addresses the long-term prediction problem of nonlinear dynamical systems by leveraging the Koopman Autoencoder (KAE) model. To improve the long-term prediction performance of KAE on nonlinear systems, we propose a multi-input-based KAE model that utilizes high temporal resolution multi-input data instead of lowering the temporal resolution of the model prediction. We validated the effectiveness of the proposed method through MSE, MAPE, and SMAPE metrics on three nonlinear dynamical system datasets? Navier-Stokes (smoke), Navier-Stokes (viscous flow), and Shallow-Water, showing significant improvement over baseline models.

https://doi.org/10.5370/KIEE.2024.73.11.2011

이민형(Min-Hyung Lee) ; 김도현(Do-Hyun Kim) ; 안희영(Hee-Young Ahn) ; 이영기(Young-Ki Lee) ; 한유근(Eu-Geun Han) ; 임소진(So-Jin Lim) ; 김경호(Kyung-Ho Kim)

Although various plans for future warfare are being discussed, no research has been published on a targeting device that predicts the aiming point of a target using the DaSiameseRPN algorithm, nor has any study demonstrated its real-time operation on a hardware accelerator. To process DaSiameseRPN in real-time on a hardware accelerator, an AI model that compensates for the accuracy loss caused by model compression was applied. This paper presents a novel approach to real-time target aiming by processing Image Tracer, DaSiameseRPN, and the Lucas-Kanade Algorithm on a hardware accelerator. The primary goal of this research is to accurately determine the aiming point of a moving target by leveraging advanced AI techniques in a real-time embedded system. To achieve real-time performance, we implemented fine-tuning, transfer learning, and model compression, enabling the AI algorithms to operate efficiently on the hardware platform. The effectiveness of our approach was validated through comprehensive analyses, including motion vector extraction, linear regression analysis, and aim point error rate evaluation. The results demonstrate a substantial improvement in accuracy, with the AI system consistently predicting target positions with minimal error. Specifically, the integration of brightness clipping and linear regression led to a notable reduction in aiming errors, making the system more reliable in dynamic environments. Moreover, the system's ability to process complex AI algorithms in real-time on a hardware accelerator opens up new possibilities for deploying similar technologies in various real-world applications. The findings of this study confirm that the proposed method not only meets real-time requirements but also enhances the precision of target aiming, which is critical for applications such as defense systems, autonomous vehicles, and advanced surveillance systems. In conclusion, this research contributes to the field of AI-driven target tracking by providing a robust, real-time solution that can be implemented on hardware accelerators, thereby advancing the capabilities of current aiming technologies.

https://doi.org/10.5370/KIEE.2024.73.11.2019

김준혁(Jun-Hyeok Kim)

The increasing complexity of power systems has made traditional analysis methods less effective, leading to the application of artificial intelligence (AI) in the power system. This study develops a domain-specific chatbot using generative AI to interpret regulations related to distributed energy resources (DERs) in South Korea, trained on KEPCO’s "Technical Standards for the Connection of Distributed Energy Resources to Distribution Systems." The chatbot uses keyword-based retrieval and sentence generation to answer queries on terms like "surge" "flicker" and "harmonics". Challenges such as sentence coherence in complex queries were identified. To address this, the Llama-based model and keyword-based information retrieval methods are utilized. Despite these challenges, the chatbot shows strong potential for improving regulatory information access and user interactions in the power sector.

https://doi.org/10.5370/KIEE.2024.73.11.2024

이상정(Sang-Jeong Lee) ; 서성발(Sung-Bal Seo) ; 배유석(You-Suk Bae)

We developed a visual inspection method for PCB board using an anomaly detection model. To improve feature extraction performance, we developed and optimized the feature extractor by comparing three types of backbone models. Then we compared two anomaly detection models with developed feature extractor as a backbone for visual inspection. Finally, we found the optimized loss function named mean-shifted contrastive loss which showed the highest accuracy in our experiment.

https://doi.org/10.5370/KIEE.2024.73.11.2030

김수용(Su-Yong Kim) ; 원종빈(Jong-Bin Won) ; 민준혁(Jun-Hyuk Min) ; 정성인(Sung-In Jeong)

As global warming accelerates due to greenhouse gases, various industries are making significant efforts to reduce greenhouse gas emissions. The automotive industry is also following the environmental policies of developed countries to achieve carbon neutrality, including exhaust gas regulations. Especially, the transportation field the largest contributor to greenhouse gas emissions, accounting for 30% of total emissions. In this study, it deals with the effective heat management of eco-friendly vehicles such as electric cars and hydrogen vehicles. Hydrogen fuel cells generate electricity and water through the combination of hydrogen and oxygen, releasing a significant amount of heat in the process. For hydrogen fuel cell vehicles, managing this heat is necessary for the vehicle's durability, making research on thermal management systems essential. This paper compares and analyzes the performance characteristics of a 10kW fan motor used in the thermal management system of hydrogen fuel cell buses, based on different pole-slot combinations. The no-load and load performance of the 16-pole and 24-slot combination as well as the 20-pole and 24-slot combination were compared, focusing on various characteristics such as cogging torque, torque ripple, radial force, and efficiency. The results indicate that the 20-pole 24-slot combination exhibited superior performance in terms of cogging torque and torque ripple.

https://doi.org/10.5370/KIEE.2024.73.11.2036

김예중(Yejung Kim) ; 송주원(Juwon Song) ; 김명진(Myungchin Kim)

This paper discusses an approach designed to mitigate overvoltage issues that can occur during islanded operation of inverter based distributed generation (DG) sources as a result of single-line-to-ground (SLG) faults. The overvoltage was reduced by modifying the inverter output command by using an overvoltage mitigation coefficient in the inverter control logic. Real-time simulations were conducted to validate the effectiveness of the proposed approach. Verficiation results showed that the proposed overvoltage mtigation approach contributed to reducing the overvoltage caused during islanded operation and ensures satisfactory operation of the distribution network operated by inverter based DG sources. Additionally, the study compares the two detection methods and finds that the instantaneous voltage detection-based overvoltage mitigation algorithm excels in responsiveness, while the RMS voltage detection-based algorithm provides a greater overall reduction in overvoltage. Not only the proposed approach contributes to addressing overvoltage concerns as a result of temporary SLG faults and islanded operation, but also could be integrated to existing inverter control algorithms with minimal effort.

https://doi.org/10.5370/KIEE.2024.73.11.2045

김민재(Min-Jae Kim) ; 방준호(Junho Bang) ; 김든찬(Deunchan Kim) ; 김지원(Ji-Won Kim) ; 박소연(Soyeon Park) ; 강해권(Hae-Gweon Kang) ; 권명회(Myeong-Hoi Kwon)

Offshore wind power is gaining attraction as a sustainable energy solution, but optimizing topologies for changing environments remains a significant challenge. Existing algorithms design static topologies based on specific environmental conditions, which limits the flexibility of real-time adaptation. In this study, we propose a dynamic topology optimization technique using deep Q-networks (DQN) to address this problem. We model offshore wind farm topology optimization as a Markov decision process (MDP) and apply DQNs to solve it in real-time. Experiments are conducted through simulations using an offshore wind farm model with 40 wind turbines (5MW). DQN-based optimization achieved an annual energy production of 894.7 GWh and an average transmission loss rate of 4.80%, outperforming the fixed topology and random breaker switching methods. DQN showed high adaptability to seasonal wind direction changes and power demand fluctuations, maintaining stable performance throughout the year.

https://doi.org/10.5370/KIEE.2024.73.11.2053

이동주(Dong-Ju Lee) ; 김종겸(Jong-Gyeum Kim)

Induction motors are often used in conveyor systems of logistics facilities because they are most efficient when operating at constant speed. Since the torque of an induction motor changes depending on the size of the load, it has the characteristic that the power factor also changes with changes in the power. Induction motors are typical inductive loads, and because they have a power factor lower than that required by power companies, they almost always require the installation of compensation devices such as capacitors. Since the load to be transported by the conveyor system varies in size and weight, the torque of the induction motor that operates it also varies from moment to moment. When the torque of an induction motor changes, the amount of reactive power required for magnetization changes little, but the change in active power changes greatly, so the change in power factor increases. Since the power factor correction of an inductive load calculates the capacitor capacity based on the rated output, it is necessary to check how the power factor changes along with whether self-excitation occurs with the originally designed capacitor when the torque changes. In this study, we determined the capacity of the electric motor that can obtain the required torque in the conveyor system using formulas such as the moment of inertia, and then determined the capacity of the electric motor that can obtain the required torque in the conveyor system and each characteristic before and after the installation of capacitor was compared and analyzed.

https://doi.org/10.5370/KIEE.2024.73.11.2060

조윤진(Yun-Jin Cho) ; 조동일(Dong-Il Cho) ; 박성준(Seong-Jun Park) ; 남준혁(Jun-Hyuk Nam) ; 남태양(Tae-Yang Nam) ; 문원식(Won-Sik Moon)

This study analyzes the correlation between reliability indices and outage costs in Medium Voltage Direct Current (MVDC) systems. By evaluating key reliability indices such as SAIDI, SAIFI, and EENS, the outage costs were calculated. The analysis results show a strong positive correlation between the reliability indices and outage costs, indicating that a decrease in reliability leads to increased economic losses. Based on these findings, we propose reliability improvement strategies for the efficient and stable operation of MVDC systems. This study provides fundamental data for enhancing the reliability of MVDC systems and contributes to improving the economic efficiency of power system operations.

https://doi.org/10.5370/KIEE.2024.73.11.2069

김상암(Sang-Ahm Kim)

Railway accidents can lead to significant human casualties and economic losses, emphasizing the continuous importance of safety management. To ensure the safe operation of railway systems, it is essential to predict risks, monitor and manage key safety indicators in real-time, and implement appropriate maintenance measures as needed. Recently, various digitalized solutions have been developed to address these challenges, and ongoing research continues to explore more advanced and effective technologies and methods. This study proposes a method for identifying key monitoring factors for optimal system safety in railway operations using the Functional Resonance Analysis Method (FRAM) model. To establish a Digital Safety Chain (DSC)-based risk assessment framework, existing Event Sequence Diagram (ESD) scenarios were analyzed to identify target functions and related hazards. The FRAM model was then employed to determine the optimal contributing factors, and the effectiveness of the proposed optimal railway operation safety alternatives was validated through simulation

https://doi.org/10.5370/KIEE.2024.73.11.2078

임현성(Hyun-Sung Lim)

This paper examines the emerging field of Medium Voltage Direct Current (MVDC) systems, focusing on technological trends and electrical safety. As renewable energy integration and DC load proliferation reshape the electrical landscape, MVDC systems are becoming increasingly important. The study reviews global MVDC developments and addresses critical safety aspects unique to medium voltage DC power. Key technologies discussed include standardized network design, DC-DC converter safety, Common Mode Voltage/Current mitigation, grounding systems, protection coordination, and insulation monitoring. The report also explores comprehensive monitoring and diagnostic technologies for DC systems. Market outlook, regulatory landscape, and standardization efforts in the MVDC domain are examined. The study concludes by emphasizing the need for collaborative R&D, tailored safety standards, and the potential for MVDC to enhance grid flexibility and efficiency.

https://doi.org/10.5370/KIEE.2024.73.11.2085

이기연(Ki-Yeon Lee) ; 임승택(Seung-Taek Lim) ; 오찬혁(Chan-Hyeok Oh) ; 유인호(In-Ho Ryu) ; 박정수(Jung-Soo Park)

In recent years, the need to use DC power distribution systems has increased and there has been a growing public interest in ensuring their safety. In particular, residual current devices (RCDs) are recognised as an important piece of protective equipment for users, preventing not only equipment accidents but also personal accidents. Therefore, it is necessary to verify the operation of DC RCDs in advance. Therefore, this paper investigates a stable sensor data processing method and algorithm of DC RCDs to ensure the safety of DC electrical equipment and protect people from electric shock. DC RCDs use a fluxgate current sensor as the DC ZCT, but as the fault current increases, the pulse generation frequency increases and distortion occurs. In addition, when the fault current is such that the core is saturated, the pulse generation is interrupted and the fault current is not detected and the breaker does not operate. To solve these problems, a data processing technique has been used which applies compensation by frequency analysis of the magnetic excitation circuit of the sensor to stabilize the operating performance of the protection device. The DC RCD developed in this paper can be used as a protective device to ensure the safety of DC equipment and to protect people from electric shock, and it is judged that it will contribute to ensuring electrical safety by ensuring safety in the event of a fault and taking appropriate preventive measures by confirming the exact cause of the operation of the protective device.

https://doi.org/10.5370/KIEE.2024.73.11.2091

오찬혁(Chan?Hyeok Oh) ; 전정채(Jeong-Chay Jeon) ; 이기연(Ki?Yeon Lee) ; 임승택(Seung?Taek Lim)

In low-voltage DC systems, the grounding system is mainly a two-wire or three-wire IT system. Among them, the IT high-resistance midpoint grounding system has advantages in detecting 1-wire ground fault, but has disadvantages in continuous loss and insulation resistance measurement. This paper proposes a method to estimate the insulation resistance of the + and - lines using the measured voltage when the switch of the high-resistance midpoint is closed/opened in the open-type midpoint grounding system. Through the proposed method, it prevents continuous losses due to high-resistance midpoint grounding and allows the insulation resistance to be estimated through switch control when the measured voltage exceeds a certain value. The proposed method was verified by simulation using MATALB/SIMULINK and experiment.

https://doi.org/10.5370/KIEE.2024.73.11.2097

모영규(Young-Kyu Mo) ; 김유나(You-Na Kim) ; 태동현(Dong-Hyun Tae) ; 황민(Min Hwang) ; 우필성(Pil-Sung Woo) ; 김영석(Young-Seok Kim) ; 송길목(Kil-Mok Shong) ; 강형구진(Hyoungku Kang)

The safety of electrical facilities that supply electrical energy requires operation and management based on the balance of efficiency and reliability. To ensure the safety of electrical facilities, rational management is required to maintain the performance of the facilities that make up the facilities above a certain standard at all times. To this end, an important indicator is the degree to which the original performance and function are maintained within the period of use based on the reliability and safety of electrical facilities. Continuous diagnosis and history management are required to maintain the degree of facility's health similar to its initial performance from a maintenance perspective. In this paper, research was conducted on data structure design and life evaluation to advance the electrical equipment safety management system.

https://doi.org/10.5370/KIEE.2024.73.11.2107

박찬묵(Chan-Muk Park) ; 윤민호(Min-Ho Yoon) ; 김경탁(Kyoung-Tak Kim) ; 임성훈(Sung-Hun Lim)

In this study, we analyzed power signal characteristics under series arc fault conditions, which can occur due to poor connections or deteriorated wiring, posing significant risks to electrical systems. The research focused on examining power fluctuations caused by series arcs under controlled experimental conditions, using test specimens that simulate arc fault scenarios. Voltage and current signals were sampled at 20 kHz, enabling detailed harmonic analysis. Fast Fourier Transform (FFT) was applied to extract harmonic components within the 0-10 kHz range, specifically targeting multiples of 60 Hz. Active power (P) and reactive power (Q) were calculated for each cycle, and the results were normalized using apparent power (S) from steady-state conditions without arc faults. The analysis of power variations between successive cycles revealed distinct fluctuations linked to arc faults, providing insights into the development of more effective power signal analysis and detection techniques.

https://doi.org/10.5370/KIEE.2024.73.11.2113

강해권(Hae-Gweon Kang) ; 한가람(Ga-Ram Han) ; 전정채(Jeong-Chay Jeon) ; 방준호(Jun-Ho Bang)

Although technologies that allow the detection of abnormalities in high voltage electrical installations without power interruption are being applied, there are limitations in clearly determining facility faults. In particular, molded-type electrical equipment has a structure that completely seals internal components from the outside, making it difficult to detect internal anomalies. Therefore, it is challenging to detect early internal faults using existing power-on diagnostic method. In response, a new diagnostic method has been introduced that utilizes ultrasound to penetrate epoxy insulation and estimate the internal temperature of high-voltage molded-type transformer windings, along with a non-contact ultrasonic measurement technology. This paper, based on previous research, develops an algorithm for distinguishing between transmitted and reflected ultrasonic signals using a hybrid transmission and reception method with non-contact ultrasonic measurement technology. The performance of the algorithm was verified using high-voltage winding samples from a molded transformer specially fabricated for the experiment.

https://doi.org/10.5370/KIEE.2024.73.11.2119

정민경(Minkyung Jeong) ; 김예찬(Yechan Kim) ; 구본혁(Bonhyuk Ku) ; 강형구(Hyoungku Kang)

This paper examines the role and significance of the health index (HI) in optimizing power equipment asset management. As electrical infrastructure ages, the need for systematic evaluation tools like HI becomes critical for ensuring stable operations and reducing economic risks. In particular, this research highlights the importance of integrating AI and big data analytics to enhance failure probability predictions and customize asset management approaches based on local operational environments. It also discusses the need for systematic data collection from visual and inside inspections, online and offline diagnostics, and destructive tests, emphasizing the current challenges in South Korea's asset management practices. By addressing these limitations, the paper proposes the development of an advanced, data-driven asset management framework that can extend asset life, reduce maintenance costs, and improve the overall reliability of power networks.

https://doi.org/10.5370/KIEE.2024.73.11.2126

장주희(Ju-Hee Jang) ; 김종민(Chong-Min Kim) ; 오수정(Su-Jeong Oh)

Nowadays, the installation of photovoltaic(PV) systems integrated into structures has increased. Suitable PV systems are difficult to install with an optimal installation angle due to shape and aesthetics of architecture. This is caused by string mismatch depending on incident irradiance. Also, it is reduced the generated power of a PV system. To compensate the generated power of a PV system, a module-level power electronics(MLPEs) such as power optimizer and micro inverter is applied. Also, in some countries, building integrated photovoltaic(BIPV) systems must include a rapid shutdown function using MLPEs for safety. The MLPEs have been studied for improving the generated power. However, research on fault analysis of PV system with the MLPEs is insufficient. In this paper, short circuit fault and ground fault of a PV system are analyzed through the experimental results. A test bed is configurated with 16 series and 3 parallel and each of module is connected with a power optimizer. The short circuit fault is developed between connection of a string. When the string short circuit fault occurred, a reverse current over 500A is confirmed depending on power grid, and the module voltage is regulated to 1V. When the ground fault occurred at positive poles, the string input voltage is reduced to 16V. However, when it occurred at negative poles, the voltage is confirmed higher than inverter input voltage. As a result, at the post-accident, an optimizer is expected to be work for safety to firefighter, engineer and so on. On the other hand, it is confirmed that the accident can affect the optimizer at the time of the accident. Therefore, the PV system has to keep using protection device even using optimizer for safety.

https://doi.org/10.5370/KIEE.2024.73.11.2132

조윤진(Yun-Jin Cho) ; 조동일(Dong-Il Cho) ; 원종률(Jong-Ryul Won) ; 문원식(Won-Sik Moon)

Medium Voltage Direct Current (MVDC) technology is gaining prominence for its ability to enhance power quality, transmission efficiency, and renewable energy integration. Positioned between High Voltage Direct Current (HVDC) and Low Voltage Direct Current (LVDC), MVDC requires specialized fault detection and recovery systems due to the unique nature of DC faults. This paper examines the structure of a ±35kV Modular Multilevel Converter (MMC)-based MVDC station, identifying key fault types such as phase-to-phase (P-P) and phase-to-ground (P-G) faults. It proposes recovery procedures tailored to MVDC systems, highlighting the differences from AC systems. These findings aim to improve the operational stability and fault management of MVDC systems, providing guidance for future developments in the field.

https://doi.org/10.5370/KIEE.2024.73.11.2140

임종호(Jong-Ho Lim) ; 이재건(Jae-Gun Lee) ; 이현재(Hyun-Jae Lee) ; 김길동(Gil-Dong Kim) ; 손진근(Jin-Geun Shon)

In this paper, for the purpose of increasing the stability of railway vehicles, the performance of a leg transfer type inverter was analyzed according to the correlation between relay and change of control amount operation. For this purpose, maximum overshoot current and transient state maintenance time were analyzed according to the operation sequence and operation delay between relay operation and change of control amount during leg transfer. As a result, no direct relationship between operation correlation and maximum overshoot current was confirmed. However, it was confirmed that when the control amount is changed first, the control stability is higher as it is controlled in a steady state even in the operation delay section. Accordingly, it was verified through hardware experiments that control stability can be improved when the leg transfer type inverter for railway vehicles operates first for the control amount change during leg change.

https://doi.org/10.5370/KIEE.2024.73.11.2146

원영제(Young-Je Won) ; 이재건(Jae-Gun Lee) ; 이현재(Hyun-Jae Lee) ; 김길동(Gil-Dong Kim) ; 손진근(Jin-Geun Shon)

This paper analyzed the transient duration and maximum overshoot according to the operation delay time by applying the phase transfer method for power relay to secure fault stability in a power conversion drive system. The phase transfer method is a method of short-circuiting the faulty phase with two B-contact Power relays and connecting the neutral point to the DC link capacitor for continuous power supply. For the experiment in this study, hardware was manufactured and the power relay was synchronized to the DSP TMS320F28335. A delay was added between the operations of the B-contact power relay and the A-contact power relay to ensure stable power supply when a faulty phase occurs. The optimal relay operation sequence and operation delay time guide lines were presented. In conclusion, it is better to apply only the minimum delay when applying phase transfer method.

https://doi.org/10.5370/KIEE.2024.73.11.2152

김기표(Gi-Pyo Kim) ; 이현재(Hyun-Jae Lee) ; 김길동(Gil-Dong kim) ; 손진근(Jin-Geun Shon)

This paper explores the performance optimization of a 3-level Active Neutral Point Clamped (ANPC) inverter, focusing on its application in high-voltage, high-precision motor control systems for railway vehicles. With the increasing demand for sustainable and efficient energy solutions in the transportation sector, improving inverter efficiency and reliability is crucial. We analyze the operational principles of the 3-level ANPC inverter and compare three Pulse Width Modulation (PWM) techniques: Sinusoidal PWM (SPWM), Space Vector PWM (SVPWM), and Reference Point Saturation-based PWM (RPS-B PWM). Simulations conducted using PSIM software demonstrate that the Reference Point Saturation-based PWM technique significantly reduces total harmonic distortion (THD) and enhances power efficiency compared to SPWM and SVPWM, making it highly suitable for railway vehicle applications.

https://doi.org/10.5370/KIEE.2024.73.11.2158

이창훈(Chang-Hoon Lee) ; 최정웅(Jung-Woong Choi) ; 김소연(So-Yeon Kim) ; 송윤하(Yun-Ha Song)

As global interest in Artificial Intelligence (AI) continues to grow, the demand for data, a key resource for AI, is rapidly increasing. In the energy sector, the integration of Information and Communication Technology (ICT) is accelerating, leading to the exponential accumulation of large-scale data. However, existing energy laws and regulations remain primarily focused on energy supply and regulation, raising concerns about their ability to effectively address these evolving circumstances. This study examines the legal and institutional improvements needed to promote the sharing and utilization of energy data, based on these issues. It investigates the current status of major domestic laws and regulations related to energy data and compares them with the legal frameworks of key foreign countries, such as the United States, the United Kingdom, and Germany. Based on this analysis, the study proposes legislative improvements to enhance energy data sharing and utilization. These include establishing a national energy data sharing and utilization system, fostering a competitive environment for the free exchange of energy data, ensuring the alignment between data protection and energy data utilization, and proposing legislative and policy measures for energy data.