Faculty Profiles - KOJIMA Hiroki

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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

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

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

診断に基づく電力機器の将来性能の高精度予測方法の検討

塩見僚，金光正樹，小島寛樹，遠藤奎将，大久保仁

平成20年電気学会全国大会

SF₆ガス中リーダ放電進展に及ぼす解離生成物の影響

吉田聡，細井勇佑，小島寛樹，早川直樹，遠藤奎将，大久保仁

平成20年電気学会全国大会

SF₆ガス中における金属異物の部分放電電流パルスおよび電磁波特性に関する検討

西澤佳奈子，大楠崇司，小島寛樹，早川直樹，遠藤奎将，吉田昌展，内田克己，大久保仁

平成20年電気学会全国大会

高温超電導限流変圧器（HTc-SFCLT）用YBCO並列導体の限流特性

大村弘輝，伊藤智志，小島寛樹，早川直樹，遠藤奎将，大久保仁

平成20年電気学会全国大会

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

金光正樹，塩見僚，小島寛樹，早川直樹，遠藤奎将，大久保仁

平成20年電気学会全国大会

Novel Measurement and Analysis System for Investigation of Partial Discharge Mechanism in SF₆ Gas International conference

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

12th International Middle-East Power System Conference 2008.3.13 South Valley University

Event date： 2008.3

Language：English Presentation type：Oral presentation (general)

Venue：Aswan Country：Egypt

An understanding of mechanism of partial discharge (PD) in SF6 gas is critical for diagnosis of PD in electric power equipment and contributes to the optimization of the design of electric power applications. However, for complexity of PD characteristics under non-uniform electric field, the mechanism of PD in SF6 is not comprehended enough. For this reason, we aim to reveal the PD mechanism by measuring current waveform, propagation characteristics and light emission of PD in SF6 gas and analyzing these data. For this purpose, we have developed excellent measurement and analysis techniques. For an analysis of PD under ac voltage application, not only PD waveforms but also PD propagation property is essential. We have constructed partial discharge current pulse waveform analysis (PD-CPWA) system. This system has enabled us to observe PD current sequentially at high speed and analyze the propagation of PD current pulse statistically. By the application of PD-CPWA system to diagnosis of PD activity due to the metallic particle in SF6, we could identify the particle type and size. On the other hand, for an analysis of PD under impulse voltage application, an ultra high-speed PD measurement by various methods is extremely important. In order to investigate the impulse PD mechanism spatially and temporally, the simultaneous measurement of current and light emission intensity waveforms, streak and still light emission images and temporal evolution of spectrum of PD light emission have been carried out. By using this synchronous ultra-high speed PD measurement system, we revealed the change of light emission from decomposition products depending on the step propagation of leader discharge. © 2008 IEEE.

DOI： 10.1109/MEPCON.2008.4562383

Scopus

Other Link： https://www.webofscience.com/wos/woscc/full-record/WOS:000259262500089

Comparison of Partial Discharge Characteristics for Different Defect Types in SF₆ Gas Insulation System International conference

D. A. Mansour, T. Okusu, K. Nishizawa, H. Kojima, N. Hayakawa, F. Endo, H. Okubo

12th International Middle-East Power System Conference 2008.3.13 South Valley University

Event date： 2008.3

Language：English Presentation type：Oral presentation (general)

Venue：Aswan Country：Egypt

The high reliability, less maintenance and compact size of Gas Insulated Switchgears (GISs) have made them the primary choice for many utilities. However, sometimes insulation defects inside GIS can be a serious threat to safe operation of GIS and can lead to costly disruption of supply. As insulation failure usually starts with partial discharge (PD) activity, this paper investigates the differences in PD characteristics in SF6 gas among different types of defects. The defect types considered in this study are particles in a gas gap, particles adhered on a spacer surface and spacer/electrode detachment. Different experiments were made for sequential PD measurements using the system of PD-Current Pulse Waveform Analysis (PD-CPWA). The PD phase characteristics, PD pulse number and PD current were analyzed for the different defect types. Also the ratio of voltage increment to phase increment at the next PD pulse appearance (Δu/ΔΦ pattern) was obtained and compared for each defect type. Experimental results show that correct identification of defects can be achieved based on considered PD characteristics. © 2008 IEEE.

DOI： 10.1109/MEPCON.2008.4562335

Scopus

Other Link： https://www.webofscience.com/wos/woscc/full-record/WOS:000259262500041

機器信頼性に基づく電力システムの保守・運用の最適化

金光正樹，塩見僚，小島寛樹，早川直樹，遠藤奎将，大久保仁

電気学会誘電・絶縁材料/電線・ケーブル合同研究会 2008.2.19 電気学会誘電・絶縁材料/電線・ケーブル技術委員会

Variation of Light Emission Spectrum Depending on Partial Discharge Propagation in SF₆ Gas

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

2007.11.26

Self-recovery Characteristics of High-Tc Superconducting Fault Current Limiting Transformer (HTc-SFCLT) with 2G Coated Conductors International coauthorship

S. Ito, H. Kojima, N. Hayakawa, F. Endo, M. Noe, H. Okubo

International Symposium on EcoTopia Science 2007

Optimum Operation and Maintenance of Power Grid Based on Equipment Diagnoses

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

International Symposium on EcoTopia Science 2007

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<KOJIMA Hiroki>

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