Ji-Won Kang

Inha University

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Chae-Kyun Jung

Korea Electric Power Corporation (South Korea)

Chungyong Lee

Yonsei University

Jong-Beom Lee

Korea Institute of Industrial Technology

Dong-Wook Kim

Coriell Institute For Medical Research

Young-Ho Seo

Kwangwoon University

Jin-Kyum Kim

Kwangwoon University

Chan‐Ki Kim

Incheon National University

Tae-In Jang

Dongseung Kwon

Electronics and Telecommunications Research Institute

Byeong-Mo Yang

Korea Electric Power Corporation (South Korea)

Cooperative Institutions

Yonsei University

Korea Electric Power Corporation (South Korea)

Seoul National University

Samsung (South Korea)

Korea Advanced Institute of Science and Technology

Korea University

Hanyang University

Sungkyunkwan University

Pusan National University

Electronics and Telecommunications Research Institute

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The Development of Real-scale Power Transformer Fire and Explosion Test Method through Its Failure Mechanism Analysis

Magazine of Fire Investigation Socity of Korea (2023)

Jong-Geon Lee J.Y. Koo Hyung-Jun Ju Ji-Won Kang Hyun-Ho Choi

Failures in high voltage power transformers are classified as a kind of disaster accompanied by fires and explosions. It could lead enormous loss of property due to equipment damage and restoration, and black-out of power grid can take place by separating the fault section from the power system. In particular, power facilities including transformers have been intensively installed in Republic of Korea since the 1988 Seoul Olympics. These power equipment is operated for more than 30 years from then. The power transformers in long-term operation are aged and a number of failures tend to increase, therefore, necessity of developing transformer fire prevention and suppression technology is emerging. This paper deals with the development of 154 kV class power transformer real-scale fire test method through its fire and explosion mechanism analysis to advancement fire prevention and suppression technology on power transformer. The test method includes, test items, subjects, facilities, and test site. The established transformer fire mechanism could be applied to develop new investigation method for cause of transformer fire, and real-scale test methodology could be widely utilized for various research such as transformer fire and explosion test, development of its extinguishing technology.

Power grid

10.31345/fisk.2023.14.1.2

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A Study on SVL Transient Characteristics by Switching Overvoltage at Single Point Bonding Section in Underground Transmission Cables

The Transactions of The Korean Institute of Electrical Engineers (2014)

Chae-Kyun Jung Ji-Won Kang

This paper describes sheath voltage limiter(SVL) transient characteristics by switching overvoltage considering single point bonding in underground transmission cables. The crossbonding system is generally used for grounding methods of underground transmission system. However, the single point bonding system is used in selective area which is difficult to consist of crossbonding major section. The sheath voltage limiters are connected between joints in the single point bonding. Specially, the high overvoltage might be generated in that section as well as the aging of sheath voltage limiter might be progressed by various electrical stress including lightning overvoltage, switching overvoltage and power frequency overvoltage. Therefore, in this paper, the switching overvoltage characteristics in underground cables are firstly analysed using EMTP simulation. Then, the switching overvoltage of sheath voltage limiter is also studied in single point bonding. Finally, the reduction method of sheath voltage limiter switching overvoltage is proposed by various simulation studies including circuit breaker operating order.

Overvoltage

Limiter

Transient (computer programming)

Emtp

10.5370/kiee.2014.63.6.764

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Tomlinson-harashima precoder with tilted constellation for reducing transmission power

IEEE Transactions on Wireless Communications (2009)

Ji-Won Kang Hyungwoo Ku Dongseung Kwon Chungyong Lee

Tomlinson-Harashima precoder (THP) is being noted for an efficient alternative to dirty paper coder. THP increases the transmission power due to the use of the modulo operator. In this paper, we propose a method that reduces the transmission power by tilting the constellations of the transmit data symbols. The symbol error rate (SER) is improved for a fixed SNR by reducing the transmission power. Average transmission power is calculated asymptotically by using an extreme value distribution. We have shown that the transmission power can be significantly reduced when we use the tilted constellation THP. As the transmission power determines the SER slope, at high SNRs we achieve lower SER than in the case of a transmission over an AWGN channel. The tilted angle can be estimated at the receiver. An angle estimation algorithm is proposed that optimizes angle estimation error and SER.We use the approximation of the angle estimation error and SER to find an optimum number of tilted angles. By using the proposed angle estimation algorithm and the optimum number of tilted angles, the tilted constellation THP always outperforms the conventional THP algorithm.

Modulo operation

Transmitter power output

10.1109/twc.2009.080778

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Citations (17)

Impedance Calculation of an Underground Transmission Cable System Installed with a Sheath Current Reduction Device

KIEE International Transactions on Power Engineering (2004)

Chae-Kyun Jung Jong-Beom Lee Ji-Won Kang Xin Heng Wang Yong Song

Source

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Citations (9)

A Study on Enhancing Cybersecurity of Weapon Systems for Life-Cycle

Jouranl of Information and Security (2019)

Yong-Tae Jung Hyun-Sik Jung Ji-Won Kang

최근 국방부는 무기체계를 사이버보안의 영역에서 무기체계를 포함하였다. 기존 정보화영역에 한정되었던 사이버보안의 대 상에서 확대되고 진화된 개념이 적용되었다. 무기체계는 소프트웨어의 비중이 점차 늘어나고 있고, 사이버위협의 대상임에는 분명하다. 따라서, 사이버보안 측면에서 무기체계 수명주기간 문제점을 진단하여 무기체계 사이버보안 발전방향을 제시하고자 한다. 무기체계 사이버보안 발전을 위해서는 무기체계 소프트웨어 관리제도를 포함하여 종합적인 정책수립이 이루어져야 하 고, 이와 관련된 이해관계자들의 적극적인 참여가 필요하다.

10.33778/kcsa.2019.19.4.067

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Citations (1)

Optimal Design Method for Maximum Modulation Index of VSC HVDC based on MMC Considering Compensation Signals and AC Network Conditions

Soo-Yeon Sim Chan‐Ki Kim Ji-Won Kang

This paper deals with Modulation Index (MI) of Voltage Source Converter (VSC) HVDC System based on Modular Multilevel Converter (MMC). In the 2-level converter, the purpose of the MI is to maximize the AC voltage reference at the fixed DC voltage. Unlike 2-level converter, MMC topology is to make the converter a voltage source using capacitor. And the AC voltage reference is distorted by the circulating current, so this circulating current affects the MI. Also, the AC Network conditions such as AC voltage variation, reactive power etc., also affect the MI. It is necessary to optimize modulation index according to internal and external conditions. This paper deals with the optimization method for MI of MMC HVDC System.

Modulation index

HVDC converter station

High-voltage direct current

HVDC converter

Modulation (music)

10.23919/icpe2019-ecceasia42246.2019.8797242

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Citations (2)

Improvement of Detailed Fault Point Decision Using EMTP Analysis of Search Coil Method for HVDC Cables

The Transactions of The Korean Institute of Electrical Engineers (2011)

Chae-Kyun Jung Jinwoo Park Byeong-Mo Yang Ji-Won Kang Jong-Beom Lee

In a previous paper, the EMTP modeling technique using search coil test is established through various transient analysis including system grounding condition and grounding resistance for HVDC submarine cables. It was also proved by comparison with real test results. Based on this EMTP modeling technique, in this paper, it will be applied for modeling of ±180㎸ real HVDC submarine system(Jeju∼Haenam). This paper variously analyses the effects of fault resistance including the resistance between core and sheath, the resistance between sheath and amore and the resistance between amore and sea water through EMTP modeling of search coil method. The results can contribute to the accuracy of detailed fault point prediction of search coil test for HVDC submarine cables.

Emtp

Transient (computer programming)

10.5370/kiee.2011.60.9.1656

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Citations (1)

Self-Evolving Neural Radiance Fields

arXiv (Cornell University) (2023)

Jaewoo Jung Jisang Han Ji-Won Kang Seongchan Kim Min-Seop Kwak

Recently, neural radiance field (NeRF) has shown remarkable performance in novel view synthesis and 3D reconstruction. However, it still requires abundant high-quality images, limiting its applicability in real-world scenarios. To overcome this limitation, recent works have focused on training NeRF only with sparse viewpoints by giving additional regularizations, often called few-shot NeRF. We observe that due to the under-constrained nature of the task, solely using additional regularization is not enough to prevent the model from overfitting to sparse viewpoints. In this paper, we propose a novel framework, dubbed Self-Evolving Neural Radiance Fields (SE-NeRF), that applies a self-training framework to NeRF to address these problems. We formulate few-shot NeRF into a teacher-student framework to guide the network to learn a more robust representation of the scene by training the student with additional pseudo labels generated from the teacher. By distilling ray-level pseudo labels using distinct distillation schemes for reliable and unreliable rays obtained with our novel reliability estimation method, we enable NeRF to learn a more accurate and robust geometry of the 3D scene. We show and evaluate that applying our self-training framework to existing models improves the quality of the rendered images and achieves state-of-the-art performance in multiple settings.

Overfitting

Viewpoints

Regularization

Representation

Deep Neural Networks

10.48550/arxiv.2312.01003

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The Effect of Mechanical Wear on the Contact applied to 170㎸ Gas Insulated Switchgear(GIS)

The Transactions of The Korean Institute of Electrical Engineers (2020)

Ki-Sun Han Jong-Geon Lee Hyung-Jun Ju Ji-Won Kang

This paper deals with the effect of mechanical wear on the contact of circuit breaker applied to the 170㎸ Gas Insulated Switchgear (GIS). The arc occurrence was ignored to verify the pure effect of mechanical wear on the contact of circuit breaker. Since only the effect of the mechanical wear was considered, the experiment was carried out under no-load state. The accelerated test method was adopted and the specimens were operated until the lifetime same as actual 170㎸ GIS contact. The specimens were tripped and closed up to 20,000 times and the its electrical resistances and weights were measured at regular intervals. Based on the test results, the correlation between mechanical wear of contact and trip/close coil current was analyzed. The analysis result showed that, even the slight mechanical wear of contact can cause delays in the trop/close operation of the GIS.

Switchgear

10.5370/kiee.2020.69.11.1668

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Strategies and applications for predicting flow using neural networks: a review

JMST Advances (2024)

Ji-Won Kang Heesoo Shin Sang-Seung Lee

10.1007/s42791-024-00066-0

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