Faculty Profiles - KOJIMA Hiroki

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吉田聡，岩田健，小島寛樹，早川直樹，遠藤奎将，大久保仁

電気学会放電/誘電・絶縁材料/高電圧合同研究会

Influence of Accumulated Surface Charges on Time Transition of Partial Discharge Parameters for Micro Gap Interface in Gas Insulated Switchgear

D.-E. A. Mansour, H. Kojima, N. Hayakawa, F. Endo, H. Okubo

背後電界の影響を考慮したSF₆ガス中インパルス絶縁破壊特性

吉田聡，岩田健，小島寛樹，早川直樹，遠藤奎将，大久保仁

2008年放電学会年次大会

Partial Discharge Characteristics for Small Gap of Electrode/Epoxy Interface in SF₆ Gas International conference

D.-E. Mansour, H. Kojima, N. Hayakawa, F. Endo, H. Okubo

2008 IEEE Conference on Electrical Insulation and Dielectric Phenomena 2008.10.28 IEEE Dielectrics and Electrical Insulation Society

Event date： 2008.10

Language：English Presentation type：Poster presentation

Venue：Québec City Country：Canada

To achieve a safe operation of Gas Insulated Switchgears (GISs), the reliability of electrical insulation is one of the fundamental importance. For this respect, there is an urgent need for better understanding of partial discharge (PD) mechanisms at different locations in GIS. In the current work, the PD inception characteristics at electrode/epoxy interface at insulating spacer in GIS, which represents one of the most critical defects in GIS, are obtained and investigated with different gap lengths, 50-500 μm. Partial discharge inception voltage (PDIV) and electric field (PDIE) are measured and analyzed regarding PD inception mechanism in SF6 gas. Also the dependence of PDIV on repetitive number of PD pulses is obtained and discussed from the viewpoint of accumulated charge on the epoxy surface. © 2008 IEEE.

DOI： 10.1109/CEIDP.2008.4772884

Scopus

Other Link： https://www.webofscience.com/wos/woscc/full-record/WOS:000265875100122

SF₆ガス中絶縁破壊に至るリーダ放電の測定

吉田聡，小島寛樹，早川直樹，遠藤奎将，大久保仁

平成20年電気学会電力・エネルギー部門大会

電力システムの総合経済性を考慮した変圧器の最適保守方法(2)

塩見僚，金光正樹，小島寛樹，早川直樹，遠藤奎将，大久保仁

平成20年電気学会電力・エネルギー部門大会

SF₆ガス中リーダ放電進展に及ぼす背後電界の影響

吉田聡，小島寛樹，早川直樹，遠藤奎将，大久保仁

平成20年度電気関係学会東海支部連合大会

液体窒素/積層テープ複合絶縁系におけるハイパスフィルタを用いたインパルス部分放電測定

山口竜太郎，小島寛樹，早川直樹，遠藤奎将，大久保仁

平成20年度電気関係学会東海支部連合大会

極低温環境下における真空/固体複合絶縁系の基礎絶縁特性

大村弘輝，小島寛樹，早川直樹，遠藤奎将，平野直樹，長屋重夫，大久保仁

平成20年度電気関係学会東海支部連合大会

伝導冷却SMES用Bi2223/Agコイルにおける電流−電圧特性の温度依存性

陳シン，小島寛樹，早川直樹，遠藤奎将，大久保仁

平成20年度電気関係学会東海支部連合大会

Partial Discharge Activity and Charge Accumulation for Electrode/Epoxy Interface with Micro Gap in SF₆ Gas

D.-E. Mansour, H. Kojima, N. Hayakawa, F. Endo, H. Okubo

機器保守が送配電コスト・最適送電ルートに及ぼす影響

塩見僚，小島寛樹，早川直樹，遠藤奎将，大久保仁

平成20年度電気関係学会東海支部連合大会

Dynamic Thermal Characteristics of HTS Coil for Conduction-cooled SMES International conference

H.Kojima, X.Chen, N.Hayakawa, F.Endo, H.Okubo

2008 Applied Superconductivity Conference

Current Limiting Characteristics of Parallel-connected YBCO Coated Conductors for High-Tc Superconducting Fault Current Limiting Transformer (HTc-SFCLT) International coauthorship International conference

N. Hayakawa, K. Omura, H. Kojima, F. Endo, H. Okubo, M. Noe

2008 Applied Superconductivity Conference

電気の正体・おもしろ実験

小島寛樹

市民公開講座「電気でファッショナブルライフ、あなたも今日からエコロジスト！」（第5回）

Partial Discharge Inception Strength in a Full-scale HTS Cable Based on LN₂/Polypropylene Laminated Paper Insulation International conference

N. Hayakawa, R. Yamaguchi, H. Kojima, F. Endo, H. Okubo

2008 IEEE International Conference on Dielectric Liquids 2008.7 EHD group of the University of Poitiers

Event date： 2008.6 - 2008.7

Language：English Presentation type：Poster presentation

Venue：Poitiers Country：France

We have been discussing the partial discharge (PD) inception characteristics of liquid nitrogen (LN_2) / polypropylene (PP) laminated paper composite insulation system for high temperature superconducting (HTS) cables. Based on the volume effect on PD inception electric field strength (PDIE) with a parameter called SSLV (statistical stressed liquid volume), in this paper, we evaluated PDIE of a full-scale HTS cable sample. Experimental results revealed that PDIE of the full-scale HTS cable sample at atmospheric LN_2 pressure under AC voltage application was consistent with the minimum PDIE value in the previous experiments. These results verify that 17.4 kV_rms/mm obtained in this paper can be regarded as a criterion of PDIE in consideration of the volume effect for the practical insulation design of actual HTS cables.

DOI： 10.1109/ICDL.2008.4622518

Scopus

CiNii Research

Light Emission Spectrum Depending on Propagation of Partial Discharge in SF₆ International conference

S. Yoshida, H. Kojima, N. Hayakawa, F. Endo, H. Okubo

2008 IEEE International Symposium on Electrical Insulation 2008.6.9 IEEE DEIS

Event date： 2008.6

Language：English Presentation type：Poster presentation

Venue：Vancouver Country：Canada

An understanding of mechanism of partial discharge (PD) in SF_6 gas is critical for diagnosis of PD in electric power equipment. Moreover, analysis of PD mechanism contributes to the optimization of the design of electric power applications. For these reasons, we study in detail about PD mechanism by measuring light emission spectrum of PD in SF_6 gas. In this paper, under an application of lightning impulse voltage in needle-plane electrodes, we have measured light emission spectrum of leader discharge. As the result, we have found out the light emission of long wavelength above 560nm in leader discharge, and the light emission above 560nm is emitted in the streamer head generated at the tip of the leader channel and radiated from dissociation products depending on the step propagation of leader discharge. These results suggest that we can diagnose the PD propagation in SF_6 gas and estimate the risk of breakdown (BD) by measuring PD light emission spectrum in electric power equipment. There are possibilities to contribute to enhance performance of the diagnosis technique in gas insulated power equipment.

DOI： 10.1109/ELINSL.2008.4570350

Scopus

CiNii Research

Optimization of Asset Management and Power System Operation Based on Equipment Performance International conference

F. Endo, M. Kanamitsu, R. Shiomi, H. Kojima, N. Hayakawa, H. Okubo

2008 International Conference on Condition Monitoring and Diagnosis 2008.4.23 Beijing Area Major Laboratory of High Voltage & EMC, North China Electric Power University

Event date： 2008.4

Language：English Presentation type：Poster presentation

Venue：Beijing Country：China

Odern T&D system has the issues about economical aspects, aged equipment, reliability etc. To solve these issues, equipment should be maintained optimally and the T&D system should be operated based on the present performance of equipment. For realization of these purposes, Intelligent Grid Management System (IGMS) was proposed and its basic functions are being investigated. In this paper, failure modes of a T&D system were chronologically simulated using Monte Carlo method, and all events occurred by failures in a T&D system were evaluated as cost with nonlinear programming. The expected T&D cost was calculated by repeating these procedure many times. By minimizing the expected T&D cost, the most optimum maintenance strategies of circuit breakers and transformers were derived quantitatively.

DOI： 10.1109/CMD.2008.4580356

Scopus

Other Link： http://hdl.handle.net/2237/11798

Particle Size Identification in GIS by Ultra High Speed Measurement of Partial Discharge International conference

K. Nishizawa, T. Okusu, H. Kojima, N. Hayakawa, F. Endo, M. Yoshida, K. Uchida, H. Okubo

2008 International Conference on Condition Monitoring and Diagnosis 2008.4.22 Beijing Area Major Laboratory of High Voltage & EMC, North China Electric Power University

Event date： 2008.4

Language：English Presentation type：Poster presentation

Venue：Beijing Country：China

Gas insulated switchgear (GIS) is reliable equipment. However, when a metallic particle is in it, the insulation reliability of GIS sometimes reduces. Partial discharge (PD) measurement is usually performed to detect a metallic particle in GIS. After the PD detection, the criticality of PD must be estimated. For this purpose, identification of a particle size is very important. In this paper, every PD pulse of various particle sizes was measured sequentially with an ultra-high speed measuring system. And physical PD parameters were systematically analyzed. As a result, it was clarified that identification of the particle size was possible by considering the PD pulse number and current at positive and negative polarities. Finally, correspondence between electromagnetic wave emitted from PD and PD current was discussed.

DOI： 10.1109/CMD.2008.4580321

Scopus

CiNii Research

Dependence of Partial Discharge Characteristics at Spacer Surface on Particle Size in SF₆ Gas Insulated System International conference

N. Hayakawa, T. Okusu, K. Nishizawa, H. Kojima, F. Endo, M. Yoshida, K. Uchida, H. Okubo

2008 International Conference on Condition Monitoring and Diagnosis 2008.4.22 Beijing Area Major Laboratory of High Voltage & EMC, North China Electric Power University

Event date： 2008.4

Language：English Presentation type：Oral presentation (general)

Venue：Beijing Country：China

A metallic particle appeared in a gas insulated switchgear (GIS) sometimes adheres on a solid spacer surface. If the adhered metallic particle is exposed to a surge high voltage, a breakdown (BD) may be induced. Therefore, it is eagerly demanded to diagnose its risk correctly under the service voltage by partial discharge (PD) measurement. In this paper, particle-initiated surface PD characteristics were systematically studied in 0.4 MPa SF6 gas by changing the sizes of particles. PD inception voltage (PDIV), temporal change of PD current and the PD pulse number were analyzed in detail. Furthermore, comparing with PD characteristics of particles in a gas gap, the influence of the solid insulator on the PD characteristics was clarified. It was found out that PD characteristics greatly changed with time owing to electric charges deposited on a spacer surface. ©2007 IEEE.

DOI： 10.1109/CMD.2008.4580227

Scopus

Other Link： http://hdl.handle.net/2237/12060

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