Faculty Profiles - KOJIMA Hiroki

Presentations -

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Enhancement of Breakdown Strength by Microdischarge under Impulse Voltage Applications in Vacuum International conference

K. Aoki, R. Nishimura, H. Kojima, M. Homma, T. Shioiri, H. Okubo

24th International Symposium on Discharges and Electrical Insulation in Vacuum 2010.8.30 HTEE Institute for High-Voltage Technology and Electric Power Systems

Event date： 2010.8 - 2010.9

Language：English Presentation type：Poster presentation

Venue：Braunschweig Country：Germany

An investigation of charge behavior such as microdischarge under high electric field in vacuum is very important in order to enhance the electrical insulation performance of vacuum circuit breakers and vacuum interrupters (VCB/VI). This paper discusses the enhancement characteristics of breakdown strength by microdischarge under applying impulse voltage repeatedly and changing vacuum pressure. As a result, microdischarge which had pulsed current waveform became smaller with repeated constant peak voltage applications under 10^-6 Pa vacuum. In addition, microdischarge generation had the electrode conditioning effect to raise the breakdown voltage by reducing adsorption gas of the electrodes. Microdischarge having very small charge compared with that of breakdown has a possibility of drastic enhancement of breakdown strength in vacuum, as the non-breakdown conditioning technique.

DOI： 10.1109/DEIV.2010.5625863

Scopus

CiNii Research

Other Link： https://www.webofscience.com/wos/woscc/full-record/WOS:000287378600008

Development Mechanism of Impulse Surface Flashover on Alumina Dielectrics in Vacuum International conference

T. Ishida, H. Kojima, K. Tsuchiya, H. Okubo

24th International Symposium on Discharges and Electrical Insulation in Vacuum 2010.8.30 HTEE Institute for High-Voltage Technology and Electric Power Systems

Event date： 2010.8 - 2010.9

Language：English Presentation type：Poster presentation

Venue：Braunschweig Country：Germany

We investigated the development mechanism of impulse surface flashover on alumina ceramic insulator in vacuum. We measured the still image and framing image of fast developing surface flashover in synchronous with applied impulse voltage and current waveforms. The light emission transition in initiation of surface flashover was clarified. We found the dark area is formed around the cathode and conducting channel is formed from the anode in developing process of surface flashover in vacuum.

DOI： 10.1109/DEIV.2010.5625860

Scopus

CiNii Research

Other Link： https://www.webofscience.com/wos/woscc/full-record/WOS:000287378600023

Current Limiting and Recovery Characteristics of 2MVA Class Superconducting Fault Current Limiting Transformer (SFCLT) International conference

2010 Applied Superconductivity Conference

Progress in Development of Superconducting Fault Current Limiting Transformer (SFCLT) International conference

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

Applied Superconductivity Conference

Feasibility Study on High Temperature Superconducting Fault Current Limiting Cable (HTS-FCL Cable) Using Flux Flow Resistance International conference

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

Applied Superconductivity Conference

Analysis of Current Limiting and Recovery Characteristics of Superconducting Fault Current Limiting Transformer (SFCLT) with YBCO Coated Conductors International conference

T. Kito, M. Kotari, H. Kojima, N. Hayakawa, F. Endo, H. Okubo

Applied Superconductivity Conference

Current Limiting Characteristics of HTS Fault Current Limiting Cable (HTS-FCL Cable) Using Flux Flow Resistance

F. Kato, H. Kojima, N. Hayakawa, M. Hanai, H. Okubo

2010.6.10

Electrical Insulation Performance of Superconducting Coil Model for Conduction-cooled SMES

N. Inoue, H. Kojima, N. Hayakawa, M. Hanai, K. Shikimachi, N. Hirano, S. Nagaya, H. Okubo

2010.6.11

Optimization of Asset Management in High Voltage Substation Based on Equipment Monitoring and Power System Operation International conference

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

2010 IEEE International Symposium on Electrical Insulation 2010.6.9 IEEE Dielectrics and Electrical Insulation Society

Event date： 2010.6

Language：English Presentation type：Symposium, workshop panel (public)

Venue：San Diego Country：United States

This paper presents a new optimization approach of maintenance strategy for equipment in a transmission and distribution (T&D) system. In this approach, a present and future equipment performance is estimated by using monitoring data, and impacts of performance in each equipment on a whole T&D system are evaluated. By minimizing the impacts, suitable maintenance procedures and timing are derived. This approach is applied to a circuit breaker (CB) in an electric network, and its significance and usefulness are presented.

DOI： 10.1109/ELINSL.2010.5549579

Scopus

CiNii Research

Other Link： https://www.webofscience.com/wos/woscc/full-record/WOS:000287026500039

真空バルブ内電極の電界最適化自動計算における最適収束条件の検討

鈴木啓也，加藤克巳，小島寛樹，大久保仁

平成22年電気学会全国大会