https://doi.org/10.5370/KIEE.2024.73.8.1271

권혁일(Hyuk-Il Kwon) ; 구현근(Hyun-Keun Ku) ; 오승찬(Seung-Chan Oh) ; 이재걸(Jae-Gul Lee) ; 신정훈(Jeong-Hoon Shin)

Countries worldwide are announcing carbon reduction targets as part of their environmental policies. Similarly, in Korea, sector-specific carbon reduction plans have been announced to achieve carbon neutrality by 2050. In the transition sector, goals have been set for power generation based on renewable energy sources. However, due to the distant timeframe of 2050, there is a possibility of changes in the composition goals of power sources based on government policies and technological trends. Consequently, frequent scenario reviews are required to formulate new plans accordingly. In this regard, there is a need for a relatively concise and rapid analysis method and tool to structure and analyze data concerning the uncertain long-term future composition of power sources. However, the power system analysis tool PSS/E, which is utilized by Korea Electric Power Corporation, involves considerable work time for data stabilization for interpretation. Therefore, this paper introduces an interarea power flow analysis tool based on DC power flow calculation, developed for quick and efficient analysis of active power flow. It demonstrates its capability to swiftly analyze various generation composition scenarios, contributing to long-term system planning. Furthermore, the accuracy of the development tool was confirmed through detailed comparative analysis using PSS/E. The case study was conducted targeting the 2050 carbon-neutral power system and describes the analysis results.

https://doi.org/10.5370/KIEE.2024.73.8.1280

김영범(Yeong-Beom Kim) ; 민재현(Jae-Hyun Min) ; 남윤호(Yun-Ho Nam) ; 조윤성(Yoon-Sung Cho)

As the penetration of Variable Renewable Energy (VRE) increases, the power system may face risks of frequency decline due to the degradation of system inertia and an increase in the Rate of Change of Frequency (RoCoF). The negative impact on frequency stability highlights the importance of establishing Under Frequency Relay (UFR) as well as defining procedures and criteria for frequency decline protection. For UFR analysis, real performance data is extracted based on the current electrical facilities and loads connected to the system. By reflecting this extracted data, system constants are calculated, and through these constants, frequency computations over time are conducted to establish optimal operating strategies for UFR. In other words, current methods of establishing UFR standards are based on real data. However, this paper analyzes UFR standards in operation using the Power Simulation Simulator for Engineering (PSS/E), a large-scale power system analysis program, establishes an optimal UFR operation plan for the system, and targets future systems that are planned but not yet connected

https://doi.org/10.5370/KIEE.2024.73.8.1291

한창희(Changhee Han) ; 최재석(Jaeseok Choi) ; 장길수(Gilsoo Jang)

This study proposed a stochastic optimization-based operation strategy of medium-voltage dc (MTDC) system which can regulate power flows in distribution networks (DNs). We considered the uncertainty from forecast errors of photovoltaic (PV) and load output, using distributionally robust chance constrained optimization method. For optimally operating the MTDC system in DNs, the proposed method stochastically relaxes the reliability constraints on the bus voltage and branch power flow, to maximize the cost-benefit of the DNs. Through numerical comparisons of the simulation results, we showed that the distribution system operator can achieve economic efficiency for imported electricity by relaxing conservativeness in reliability of DNs.

https://doi.org/10.5370/KIEE.2024.73.8.1298

이혜규(Hye-Gyu Lee) ; 황평익(Pyeong-Ik Hwang)

The section load corresponds to the total load in a section that is surrounded by a circuit breaker CB) and/or automatic switches （ (ASWs). Because various applications provided by an advanced distribution management system, such as volt/var optimization and dynamic network reconfiguration, require accurate distribution system model including the power consumption of loads, the importance of the accurate section load estimation is increasing. If the active and reactive power measurements are accurate, the section load can be estimated with simple methods. However, the voltage magnitude measured by an ASW is often inaccurate, leading to erroneous active and reactive power measurements. Thus, only the current magnitude and the power factor angle, which are more accurate, are generally used to estimate the section load in the actual system. The main idea of the proposed method is that the reliable measurements of ASWs correspond to the parameters for a constant current load model, i.e., current magnitude and power factor angle. Therefore, ASWs can be modeled as constant current loads in the estimation problem. Based on this idea, a new section load estimation method is proposed, utilizing the forward/backward sweep power flow method, which is easy to incorporate with the constant current load model. Simulation results verify that the accuracy of the section load estimation is improved with the proposed method compared to a conventional method.

https://doi.org/10.5370/KIEE.2024.73.8.1306

이제원(Jae-Won Lee) ; 이근준(Geun-Joon Lee)

This paper discusses the mechanism of power trading based on the incremental reliability and incremental economy when a renewable energy-based standalone microgrid designed to have a certain level of supply reliability operates in coordination with other microgrids and the main grid. It examines the reliability and economy of the new power grid formed during coordination and demonstrates that the reliability and economy of micro-grids based on solar and wind power vary in load supply reliability due to the uncontrollability and intermittency/variability of output. Additionally, it shows that these factors can be altered by the introduction of energy storage systems and backup power supplies, allowing for reliability-economy trades that consider their differences during integrated operation of microgrids. Suggested method is applied and verified to PV and Wind microgrid interconnection and Jeju island, and showed the benfits and losses of interconnection. Also, the effects of source variability on LCOE at different demand style are discussed and suggested.

https://doi.org/10.5370/KIEE.2024.73.8.1311

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

Starting current of induction motor is briefly high for a second and its starting current causes misoperation of protective devices such as over current relay, which can be lead to a large blackout. To prevent misoperation of protective devices, superconducting fault current limiter (SFCL) can be expected to be suitable method to limit starting current of induction motor because SFCL can perform the fault current limiting operation without additional detecting devices. Among the developed SFCLs, the transformer type SFCL has the merit easily to adjust the operational current by setting the turns ratio between the primary and the secondary windings. In this paper, the induction motor’s starting current limiting characteristics due to three-phase reactor type SFCL were analyzed together with its voltage drop suppressing operation. As its starting method, both wye and delta starting operations of the induction motor were selected and the operational characteristics of the SFCL were compared.

https://doi.org/10.5370/KIEE.2024.73.8.1318

이경영(Kyeong-Yeong Lee) ; 임세헌(Se-Heon Lim) ; 김태근(Tae-Geun Kim) ; 송경민(Kyung-Min Song) ; 윤성국(Sung-Guk Yoon)

Transmission line fault data plays an important role in power system reliability analysis and fault prediction. However, real fault data is not enough because transmission line faults do not frequently happen. To obtain various fault data, we propose a generative adversarial network (GAN)-based data augmentation technique. The proposed technique consists of three steps. i) it generates fault data using the wasserstein GAN with gradient penalty (WGAN-GP) model. ii) the generated data is filtered through an isolation forest (IF) algorithm, and iii) the filtered data is evaluated for its quality through KL-divergence. We visually showed that the proposed technique's data generation performance in terms of data diversity. It is also confirmed that the generated data is closer to the real fault data than the simulated data.

https://doi.org/10.5370/KIEE.2024.73.8.1327

이경민(Kyung-Min Lee) ; 박철원(Chul-Won Park)

Recently, as it is time to replace hydraulic power equipment, modernization projects are being promoted. In addition, industrial competitiveness is being secured through localization of core technologies for main and auxiliary devices in the field of hydropower and pumped storage. In order to pioneer new overseas market, it is necessary to proactively apply AI techniques to improve the next-generation hydropower generator system. In this paper, to attempt an intelligent IED, we propose a comparison of pattern recognition techniques using machine learning for loss of excitation and power swing, and verify the performance by comparing the pattern recognition results of two AI techniques, such as SVM and LSTM.

https://doi.org/10.5370/KIEE.2024.73.8.1333

김민우(Minwoo Kim) ; 조봉현(Bonghyun Cho) ; 이지호(Jiho Lee)

Selecting an optimal DAQ instrument is crucial for testing high-temperature superconducting (HTS) devices, especially for microvolt scale voltage measurement. The widely-used SCXI-1125 from National Instruments is discontinued, leading us to conduct a comprehensive analysis for an alternative. We evaluated PXIe-4300, SCXI-1125, DT9824, and PXIe-4302, comparing their performance in experiments on the critical current of RE-Ba-Cu-O composite superconducting wire and small-scale voltage. Based on test results, we identified the most suitable DAQ instrument for our research project aiming to develop an HTS D-shape toroidal magnet and high-current cable for a fusion reactor and superconducting magnetic energy storage.

https://doi.org/10.5370/KIEE.2024.73.8.1339

김진훈(Jinhun Kim) ; 윤효원(Hyowon Yoon) ; 박영은(Yeongeun Park) ; 김상엽(Sangyeob Kim) ; 강규혁(Gyuhyeok Kang) ; 백두산(Dusan Baek) ; 박수민(Sumin Park) ; 석오균(Ogyun Seok)

SiC double trench MOSFETs have the advantage of generating a deep P+ layers through the trench source, effectively mitigating electric field crowding at the bottom edge of the gate oxide. However, the depletion region induced by the deep P+ layers narrows the current path between the gate and P+ , resulting in an increase in the on-resistance. In this study, we addressed this problem by introducing CSLs through ion implantation in the 1.2 kV SiC double trench MOSFETs. CSL concentration optimization resulted in a 3.92 % decrease in on-resistance and a 3.19 % increase in the figure of merit. Therefore, the SiC double trench MOSFET with optimized CSL concentration has improved on-resistance characteristics and figure of merit compared to the conventional structure.

https://doi.org/10.5370/KIEE.2024.73.8.1344

남상민(Sangmin Nam) ; 장성욱(Sung-Uk Zhang)

With the expansion of the power semiconductor market, the reliability issues of power semiconductors have become increasingly important. The package process involves wafer saw, bonding, molding, and Die-attach processes. In the Die-attach process, sintered Ag material using a sintering process is used. If voids occur in this process, it can lead to an increase in the device's temperature. In this study, a comparative analysis was conducted using TO-251 and TO-252 packages. We examined the maximum junction temperature, power dissipation, and thermal resistance, investigating the impact of voids on the package. Additionally, we explored changes in thermal characteristics based on variations in wire diameter.

https://doi.org/10.5370/KIEE.2024.73.8.1351

최나연(Na-Yeon Choi) ; 장성욱(Sung-Uk Zhang)

The growing demand for wireless communication technology, especially in the field of mobile communications and the expansion of 5G services, is driving the demand for RF devices, one of its core components. An important core technology in wireless communication systems is the communication between base stations and artificial satellites, and between satellites and satellites. Space environments such as artificial satellites require the utilization of hermetic packages that require high reliability and durability. Hermetic package refers to the use of metal and ceramic materials to seal the package under vacuum after assembly. Although it is relatively expensive compared to plastic packages, it has been utilized in industries that require high reliability due to its durability, electrical insulation, and power saving. In this study, we utilized finite element analysis to model the situation of hermetic package using GaN HEMT device, which is a popular RF device used in satellite communication, and compared and analyzed the electrical and thermal properties according to voids that may occur at the core of the packaging process and the change of wire thickness process conditions.

https://doi.org/10.5370/KIEE.2024.73.8.1360

윤기하(Giha Yoon) ; 김근용(Geunyong Kim) ; 유학(Hark Yoo) ; 김성창(Sung-Chang Kim) ; 김재인(Jaein Kim)

In this paper, we propose an edge computing-based gateway system (EGW) for the efficient collection of sensor data from transmission lines in AC/DC hybrid distribution networks. The proposed system allows for parallel collection of sensor data, enabling the detection of instantaneous electrical events, such as voltage sags, without omission. It also provides a hardware-based event detection function for rapid identification of sudden abnormal events. Additionally, the EGW offers IEEE 1588v2(PTP)-based time synchronization to accurately estimate the location of events on transmission lines. The edge gateway was implemented on an FPGA-based test board, and performance tests were conducted in a simulated laboratory environment. In a Peer-to-Peer setting, the time synchronization error was approximately ±30ns. The sensor data collection performance for parallel channels showed that the collection time for one channel was identical to that for four channels. Moreover, the hardware-based event detection module was able to detect events within an average of 560 s after data injection, with a deviation of about 100 s. The edge gateway will be μ μ applied to the MVDC testbed at the KEPCO for collecting sensor data from DC transmission test line. Then, the system will be further developed into a fully operational product for the AC/DC hybrid distribution network testbed.

https://doi.org/10.5370/KIEE.2024.73.8.1369

이상준(SangJoon Lee) ; 이현용(Hyunyong Lee) ; 고석갑(Seok-Kap Ko)

Energy storage system(ESS) based on rechargeable battery have varying energy efficiency depending on its internal resistance. Among the many factors that affect the internal resistance, temperature is one of the major factor. The external temperature of ESS operating environment can be controlled to improve the energy efficiency, however such control comes with its own cost. The recent development of internet of things(IoT) technology and time-series forecasting allows the ESS operator to monitor and predict the short-term external environment. In this paper we model a scenario which low outside temperature may affect the battery internal resistance, and compare the net cost under various temperature control scheme. We show that adequate temperature control based on short-term forecast is more beneficial than the baseline scheme of no control.

https://doi.org/10.5370/KIEE.2024.73.8.1376

박상준(Sangjun Park) ; 이형옥(Hyungok Lee) ; 황유민(Yumin Hwang) ; 이준기(Jungi Lee) ; 김낙우(Nacwoo Kim) ; 이현용(Hyunyong Lee) ; 고석갑(Seokkap Ko)

Digital twin has gained attentions in the literature because it enables us to either estimate future states of a system or prevent its fault failures. To successfully apply digital twin into a system, a model of the system has to be accurately identified. Koopman Operator Theorey proved in 1931 sheds light on the system identification because it makes us interpret a nonlinear dynamical system as a linear system. Nowdays, deep learning technoloiges with the theory have been used for the system identification. We herein aim to review a model named as Koopman Autoencoder (KAE), which is considered to be baseline in the literature, and propose a new training/inference strategy to improve the performance of KAE for future estimation. To demonstrate advantages of our strategy, we develop two KAE models with/without our strategy, using synthetic datasets generated with the IEEE 3-Bus system. We show that KAE with the strategy can achieve a better performance with respect to mean squared error and relative root mean squared error, compared to KAE without it.

https://doi.org/10.5370/KIEE.2024.73.8.1384

박명혜(Myung-Hye Park) ; 김영현(Young-Hyun Kim) ; 은창수(Chang-Soo Eun)

Since the implementation of the Serious Accident Punishment Act, various attempts have been made in the field to prevent safety accidents and respond quickly when accidents occur. In particular, building a safety management operation system that monitors the site in real time using IoT technology is an issue. In this paper, we develop video inference technology using CCTV as a way to prevent worker safety accidents in high-risk industrial sites such as power plants. Based on this, we develop functions to detect worker falls, entry into hazardous areas, and fires in real time. We would like to introduce an intelligent worker safety control system implemented to control field events

https://doi.org/10.5370/KIEE.2024.73.8.1390

김영현(Younghyun Kim) ; 박명혜(Myung-Hye Park) ; 은창수(Chang-Soo Eun)

To enhance the integration of renewable energy and ensure the stable deployment and operation of smart grids, effective management of power equipment is crucial. Establishing a reliable communication network between field devices and operational systems is essential to meet these requirements. Specifically, communication technologies in power grids must offer high reliability and low latency to prevent incidents and enable quick post-event responses. This paper explores licensed-band wireless communication technologies and operational strategies suitable for use in power settings. Additionally, we demonstrate through empirical validation that the proposed technologies can provide stable communication performance, enabling effective power equipment management services.

https://doi.org/10.5370/KIEE.2024.73.8.1396

안병현(Byeong-Hyeon An) ; 오정식(Jeong-Sik Oh) ; 김태훈(Tae-Hun Kim) ; 박재덕(Jae-Deok Park) ; 이형운(Hyoung-Woon Lee) ; 박태식(Tae-Sik Park)

Failures in power facilities can cause unplanned outages, leading to significant costs and secondary impacts such as production losses, human casualties, and social disruption. Therefore, high reliability is crucial. Power facility asset management technology evaluates condition, lifespan, and risk costs over the equipment's lifecycle, formulating optimal maintenance and replacement strategies to maximize facility value by maintaining high reliability while minimizing costs. This paper aims to establish an optimal asset management system by selecting targets and maintenance strategies based on facility risk levels, using an extended FMEA-based RPN method. Maintenance strategies are selected through investment feasibility assessments considering design lifespan, failure impacts, and replacement costs

https://doi.org/10.5370/KIEE.2024.73.8.1404

오정식(Jeong-Sik Oh) ; 김태훈(Tae-Hoon Kim) ; 안병현(Byeong-Hyeon An) ; 이승윤(Seung-Yoon Lee) ; 임선우(Seon-Woo Lim) ; 박태식(Tae-Sik Park)

For utility companies that own power grids, it is crucial not only to generate revenue through power supply services but also to efficiently manage their power facility assets to reduce unnecessary expenditures. In particular, if unforeseen accidents occur due to the deterioration or failure of power facilities, it is important for utility companies to prevent critical risks such as incurring costs for damage compensation and a decline in social image, in line with their obligation to provide a stable power supply. To this end, it is essential for utility companies to develop strategies for the replacement of power facilities in addition to continuous maintenance. In this paper, NPV(Net Present Value) and BCR(Benefit-Cost Ratio) methods to prioritizing investment in power facilities are compared and analyzed in terms of cables, transformers, and lightning arresters.

https://doi.org/10.5370/KIEE.2024.73.8.1412

구본혁(Bonhyuk Ku) ; 정민경(Minkyung Jeong) ; 김예찬(Yechan Kim) ; 이호빈(Hobin Lee) ; 김재상(Jaesang Kim) ; 박준영(Junyoung Park) ; (Herviana) ; 강형구(Hyoungku Kang)

This study focuses on enhancing MV (Medium Voltage) switchgear asset management efficiency through life extension strategies. It includes an analysis of MV switchgear configurations, international practices, and successful life extension cases. The analysis identifies key components, roles, and maintenance needs. By examining international case studies, the research highlights advanced techniques and strategies from developed countries. The study explores technologies and methods effective in prolonging MV switchgear lifespan, emphasizing systematic health assessments such as continuous monitoring, inspection, and testing. Based on these assessments, economic evaluations determine the need for refurbishment, retrofit, and remanufacturing. Implementing these strategies improves the reliability of electrical systems and supports resource circulation, carbon neutrality, and ESG (Environmental, Social, and Governance) management.

https://doi.org/10.5370/KIEE.2024.73.8.1422

고재원(Jaewon Koh) ; 김우곤(Woogon Kim) ; 서성부(Seongbu Seo) ; 서예준(Yejune seo) ; 김기윤(Kiyun Kim) ; 강승택(Sungtek Kahng)

In order to enhance the power of the received signal between the millimeter-wave transmitting and receiving antennas, three structures are proposed based on the use of metasurfaces. Structure 1 is a non-tilting metasurface between millimeter-wave antennas at port 1 and port 2. Structure 2 lays the tilted to the right, non-tilting and tilted to the left metasurfaces from the left through the center to the right areas on the same layer. Structure 3 places structure 2 over another of the same kind. Experiments on structure 1 as the building block and structures 2 and 3 as augmented metamaterials give increment of around 7 dB, 9 dB and 14 dB in the level of the received signal. Considering volumes as small as 7.0 7.0 3.0 cm3 and 21.0 7.0 6.5 cm3 for structure 1 and ? ? ? ? structures 2 and 3, respectively, it will turn out to be useful in making millimeter-wave antennas deterring fast path loss.

https://doi.org/10.5370/KIEE.2024.73.8.1429

노석범(Seok-Beom Roh) ; 오성권(Sung-Kwun Oh)

In this study, we introduce an ensemble model that leverages a radial basis function neural network as the base model to enhance the classification performance of a pattern classifier. While existing ensemble models use the majority vote technique for aggregation, we proposes a new aggregation method that combines a simple linear function and a softmax function, using the outputs of the base model as input variables. This aggregation approach linearly combines the class prediction probabilities from each base model to calculate the class-specific probability for the ensemble model. To evaluate the performance of the proposed pattern classifier, we used 14 datasets to optimize the parameters of the linear function and compared the performance with existing pattern classifiers. Our method achieved better results on 10 out of the 14 datasets compared to other pattern classifiers. Additionally, when compared with a recently reported ensemble model, our method also demonstrated superior performance.

https://doi.org/10.5370/KIEE.2024.73.8.1437

김성수(Sung-Soo Kim)

Conjugate gradient methods are optimization techniques used to minimize cost functions in nonconvex problem domains. However, in non-quadratic conjugate gradient methods, challenges often arise due to exact line searches and the need for effective restart procedures to enhance convergence properties. This paper introduces a modified conjugate gradient method that incorporates adaptive restarting, specifically designed for nonconvex objective functions, with the goal of preventing stagnation in convergence iterations. The adaptive restarting conjugate gradient approach aims to increase the likelihood of eliminating convergence stagnation. Through numerical investigations, the paper demonstrates the superior performance of the proposed restarting method, showcasing improved convergence behavior by effectively mitigating stagnation in the convergence process.

https://doi.org/10.5370/KIEE.2024.73.8.1449

방수철(Su-Chul Bang) ; 윤용호(Yong-Ho Yoon)

BMS (Battery Management System) monitors the battery's temperature, voltage, and current to determine the current state of the battery and protects the battery by responding to abnormal signals such as overcurrent and overvoltage. Additionally, the BMS uses cell balancing techniques to prevent fires and explosions caused by overcharging due to voltage imbalance between battery cells and improve the overall lifespan and safety of the battery. Therefore, in this paper, a test facility using a passive cell balancing technique was constructed to examine the charging characteristics of lithium-ion battery cells due to the voltage imbalance phenomenon. Using this test facility, BMS operation and cell balancing characteristics of 16 lithium-ion batteries in a state of voltage imbalance between cells were tested. In addition, the characteristics of batteries in voltage balance were examined through cell balancing after being used for a certain period of time. Therefore, the performance of the battery was compared by comparing the difference in charge amount for these two conditions (voltage unbalanced state and balanced state).

https://doi.org/10.5370/KIEE.2024.73.8.1456

구자영(Ja-Young Koo) ; 곽준호(Jun-Ho Kwak) ; 김희동(Hee-Dong Kim)

A weather protected(WPII) high voltage(HV) motor stator winding has a dry band at the slot end, end-winding, and circuit ring and etc. due to environmental effects caused by the inflow of foreign substance. As a result, arcing or flashover causes insulation breakdown. This paper presents the result of an insulation diagnostic test on a WPII HV motor(2,850 kW, 6.6 kV) stator winding operated for about 4 years, where the severe contamination occurred inside of it. So, the test was performed after cleaning and drying it. The partial discharge(PD) was measured at 6,710 pC, 9,700 pC, and 12,000 pC at phase to ground voltage(3.81 kV), 1.25 times the phase to ground voltage(4.76 kV), and rated voltage(6.6 kV). The PD decreased from 12,000 pC to 10,000 pC while staying at 6.6 kV for 4 5 minutes. The pattern of PD was converted to a discharge occurring in internal delamination of ∼ groundwall insulation from a discharge of rabbit ear-like. As a result of measuring the PD while reducing the voltage again, it decreased to 7,950 pC and 3,920 pC at 4.76 kV and 3.81 kV, respectively. Based on the results of the test, we found that when fine conductive foreign substance remains on the surface of the end-winding of a HV motor, and then energizing high voltage, the foreign substance burns, showing a rabbit ear-like discharge pattern, and then disappears altogether, converting to a discharge generated from internal delamination of groundwall insulation.

https://doi.org/10.5370/KIEE.2024.73.8.1461

윤호열(Hoyeol Yoon) ; 배영철(Youngchul Bae)

This paper analyzed the cause of an insulation breakdown accident in the stator winding of a weather protected(WPII) high-voltage motor(1300kW, 6.6kV) that has been in operation for 27 years. As a result of the insulation diagnosis test conducted 1 year and 6 months before the accident, the polarization index, alternating current, and dielectric loss tangent test results were good, but the partial discharge test result was measured at 13,000pC and was evaluated as a condition requiring attention. In order to analyze the cause of the insulation breakdown of this motor, the damaged winding was cut and analyzed in detail, and no traces of insulation deterioration of the main insulator were found. Contamination was partially confirmed on the surface of the end winding, but it was also difficult to find traces of tracking. As a result of dismantling and analyzing the wires inside the winding, turn shorts were confirmed in two wires. Therefore, even if the high-voltage motor insulation diagnosis test result is judged to be good, it is necessary to comprehensively analyze the possibility of turn short circuit due to insulation deterioration inside of the main insulating material, tracking due to contamination, and deterioration of wire insulation.

https://doi.org/10.5370/KIEE.2024.73.8.1466

윤여흥(Yeoheung Yoon) ; 신제석(Je-Seok Shin) ; 이영희(Young-Hee Lee) ; 한영희(Young-Hee Han) ; 박병준(Byung-Jun Park)

Supercapacitors are attracting attention as candidates for replacing lithium-ion batteries (LiB) because of their high durability and power density. However, the energy density is only 10% of LiB, making it difficult to apply large-capacity ESS. In this study, graphene composites were pre-doped with different ratio of lithium oxide to improve the energy density of electrodes. A 30F cylindrical cell was fabricated based on the high energy density electrode materials, which was operated stably at 10C (85.6%) and 150C (71.8%). Furthermore, it showed 84.8% of specific capacitance even after 200,000 charge/discharge cycles at 100C-rate, expecting to be able to respond to ultra-short time in the frequency regulation of the power system.

https://doi.org/10.5370/KIEE.2024.73.8.1471

신제석(Je-Seok Shin) ; 김수빈(Soo-Bin Kim) ; 박병준(Byung-Jun Park) ; 박민솔(Min-Sol Park) ; 송화창(Hwa-Chang Song) ; 한영희(Young-Hee Han)

The increase in renewable energy, which has intermittent high output volatility, can cause instability to grid frequency, and the need for energy storage technology to respond flexibly to the instablility is increasing. Recently, energy storage technology using supercapacitors with improved capacity and advantages such as high output, high-speed response, and long lifespan is being developed. Supercapacitors are attracting attention as energy storage devices suitable for frequency regulation in short-cycle areas with high frequency and short duration. In this paper, we introduced a MW-class supercapacitor system and proposed its operation strategy for frequency regulation.

https://doi.org/10.5370/KIEE.2024.73.8.1476

김영달(Young-Dal Kim) ; 이승철(Seoung-Choul Lee)

Inside the distribution panel, various power devices such as transformers, VCB, and OCR are installed. The internal temperature under normal operation is approximately 40°C, and when it exceeds this temperature, the air is discharged to the outside by the ventilation fan to maintain a constant temperature. The insulating wire for wiring mainly used inside the distribution panel is HIV or KIV, and most of the insulating materials are PVC Compound, and to ensure flexibility, a thermal stabilizer and an antioxidant are mixed and used to prevent PVC from being decomposed by plasticizer and heat. The softening temperature of PVC is 65~80°C and the ignition temperature is 454°C. However, when a partial discharge occurs in a region inside the distribution panel, heat is generated at that point. When partial discharge occurs continuously, the temperature continues to rise, and the additives are gradually volatilized into gas in the insulating material from usually 100°C, thereby increasing in a large amount as the temperature increases. At this time, the gas smell, "burnt smell(phthalate and carboxylate series gas smell)", can be seen as the beginning of the deterioration phenomenon. A "fire prevention management system" was developed to prevent the occurrence of a fire in advance by detecting gas generated in such a deterioration phenomenon and determining it as a fire sign. By applying the developed system to the distribution panel, it is expected that it will not only reduce human and material damage, but also be able to cope with disaster safety accidents in advance when operating as an unmanned system.

https://doi.org/10.5370/KIEE.2024.73.8.1481

김종겸(Jong-Gyeum Kim)

Induction motors are one of the most widely used rotating machines as a driving force for rotating loads. These rotating machines are inductive loads and have different power factors during starting or when rotating at rated speed. The most commonly used method to compensate for low power factor is using a stationary reactive power compensation device such as a capacitor. Induction motors have the problem of causing a voltage drop due to the generation of high current when starting. Therefore, when the capacity of the induction motor is large, the reactor starting method is sometimes applied despite the decrease in torque due to the voltage drop. The problem with applying the reactor starting method is that it takes a long time to reach the rated speed. In the reactor starting method, the characteristics may vary depending on the installation location of the power factor correction device as well as whether or not a switch is installed in the power factor correction device. In this way, it is necessary to analyze what effect the installation of a power factor correction device has when the starting time of the induction motor becomes longer. In this study, we analyzed whether self-excitation occurs depending on the installation location of the power factor correction capacitor when starting an induction motor with a reactor.

https://doi.org/10.5370/KIEE.2024.73.8.1487

김은민(Eun-Min Kim) ; 노성여(Seong-Yeo Noh)

For secondary battery overcurrent protection devices, it is essential to perform breaking capacity tests to verify their safety in the context of explosive current events resulting from electrical mobility breakdown during the electrophoresis process and explosive fire incidents caused by post-arc phenomena. However, constructing a high-capacity DC power supply test system for breaking capacity entails considerable expenses in equipment configuration. In this study, a low-voltage high-current DC power source is employed to switch a low-current high-voltage power supply device designed an operational procedure. A system capable of conducting high breaking capacity tests with low-capacity DC power facilities is designed and confirmed the absence of statistically significant differences in the I-T curve test of overcurrent protection devices, initial current breaking capacity, and the limit test for residual arc explosion capacity. The reliability of the tests is established through comparative breaking capacity assessments with high-power supplies.

https://doi.org/10.5370/KIEE.2024.73.8.1494

김형태(Hyoungtae Kim) ; 최경식(Kyoungshik Choi) ; 박소진(Sojin Park) ; 조영아(Youngah Cho) ; 한상욱(Sangwook Han)

Korea Gas Corporation (KOGAS) imports natural gas from overseas producers, stores it at production facilities, and then vaporizes and transmits it through a nationwide primary pipeline network spanning approximately 5,000 kilometers to various pressure-regulating stations. At these stations, high-pressure natural gas (60 bar) is reduced to 35-8 bar using pressure-reducing valves before being delivered to end-users. However, the energy released during this pressure reduction process is currently unutilized and wasted. The Turbo Expander Generator represents an innovative energy generation system that harnesses this previously untapped pressure energy from the natural gas pressure reduction process at existing stations to produce electricity. By leveraging the existing infrastructure, this system minimizes the costs and potential public opposition associated with constructing new power plants, thereby proving to be an efficient distributed power source that warrants further expansion. This paper presents the characteristics of the Turbo Expander Generator, outlines the performance evaluation process for ensuring operational safety, and discusses its potential for broader integration into the power grid.