Faculty Profiles - KOJIMA Hiroki

Presentations -

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Maintenance Optimization of Power Apparatus by Intelligent Grid Management System (IGMS) and Upgrading by Partial Maintenance International conference

M. Hanai, K. Wakaiki, Y. Suzuki, H. Kojima, N. Hayakawa, H. Okubo

CIGRE SC A2 & D1 Joint Colloquium 2011

Electrical Insulation and Discharge Characteristics at HVDC Polarity Reversal in Oil/Pressboard Composite Insulation System International conference

H. Kojima, H. Saito, N. Hayakawa, K. Kato, H. Okubo

CIGRE SC A2 & D1 Joint Colloquium 2011

電力系統最適運用システム（IGMS）における保守履歴を考慮した電力機器の最適保守計画

篠田康生，若生海王，小島寛樹，早川直樹，花井正広，大久保仁

平成23年電気学会電力・エネルギー部門大会

電力系統最適運用システム（IGMS）による機器劣化を考慮した最適潮流制御

若生海王，篠田康生，小島寛樹，早川直樹，花井正広，大久保仁

平成23年電気学会電力・エネルギー部門大会

Influence of Gap Length on Discharge Channel Propagation and Breakdown Mechanism in Air International conference

H. Kojima, K. Hotta, T. Iwata, N. Hayakawa, N. Yanagita, T. Kato, T. Rokunohe, H. Okubo

17th International Symposium on High Voltage Engineering

Identification of Insulation Defect by Sequential Measurement of Partial Discharge in GIS International conference

M. Yoshida, K. Suzuki, H. Kojima, N. Hayakawa, M. Hanai, H. Okubo

17th International Symposium on High Voltage Engineering

Correlation between UHF Electromagnetic Waveforms and Partial Discharge Current Waveforms in GIS International conference

K. Suzuki, M. Yoshida, H. Kojima, N. Hayakawa, M. Hanai, H. Okubo

17th International Symposium on High Voltage Engineering

Partial Discharge Characteristics for Delamination Defect of Epoxy Cast Resin Power Apparatus International conference

D.-E.A. Mansour, H. Kojima, N. Hayakawa, M. Hanai, H. Okubo

17th International Symposium on High Voltage Engineering

Charge Behavior in Palm Fatty Acid Ester Oil (PFAE) / Pressboard Composite Insulation System with Charged Oil Flow International conference

H. Saito, H. Kojima, N. Hayakawa, K. Kato, K. Kawanishi, H. Koide, H. Okubo

2011 IEEE International Conference on Dielectric Liquids 2011.6.27 SINTEF Energy Research, Norwegian University of Science and Technology

Event date： 2011.6

Language：English Presentation type：Poster presentation

Venue：Trondheim Country：Norway

Palm Fatty Acid Ester Oil (PFAE) is expected as one of the substitutes for mineral oil of transformers owing to not only the high biodegradation but also the good insulation performance. In this paper, the electric field strength and its time transition in PFAE/Pressboard composite insulation system-under charged oil flow were directly measured by using Kerr electro-optic technique. We found that the electric field was generated by space charges in PFAE and was temporally changed with charge behavior. By comparison with high charging mineral oil, we clarified that the feature of the charge behavior in PFAE was similar to that in the mineral oil, but the behavior of electric field was different due to the variation of electric properties such as permittivity, relaxing time and charge density. © 2011 IEEE.

DOI： 10.1109/ICDL.2011.6015445

Scopus

Other Link： https://www.webofscience.com/wos/woscc/full-record/WOS:000295317700045

Discharge Mechanism at HVDC Polarity Reversal in Oil/Pressboard Composite Insulation System International conference

H. Kojima, H. Saito, N. Hayakawa, K. Kato, H. Okubo

2011 IEEE International Conference on Dielectric Liquids 2011.6.28 SINTEF Energy Research, Norwegian University of Science and Technology

Event date： 2011.6

Language：English Presentation type：Oral presentation (general)

Venue：Trondheim Country：Norway

At the instant of polarity reversal of HVDC, very high electric field was generated in oil because the applied electric field was superimposed by the electric field of accumulated charges on pressboard (PB). When the total electric field exceeded the breakdown electric field strength, breakdown discharge in oil gap and surface discharge on the PB occurred. In this paper, by electric field measurement using Kerr electro-optic technique and optical observation, breakdown discharge characteristics and mechanisms in oil / PB composite insulation system were investigated at polarity reversal voltage. We revealed that the surface discharge neutralizes the accumulated charges on PB. The above experiments were carried out for different PB arrangements and discussed the discharge characteristics under HVDC polarity reversal conditions were discussed. © 2011 IEEE.

DOI： 10.1109/ICDL.2011.6015443

Scopus

Other Link： https://www.webofscience.com/wos/woscc/full-record/WOS:000295317700043

Technical Evaluation of Current Limitation and Recovery Characteristics for Superconducting Fault Current Limiting Transformer (SFCLT)

J. Himbele, T. Kito, H. Kojima, N. Hayakawa, M. Hanai, H. Okubo

2011.6.10