Faculty Profiles - KOJIMA Hiroki

Presentations -

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Conditioning Characteristics of Multi-gap Electrode System in Vacuum

Y. Otake, R. Nishimura, H. Kojima, N. Hayakawa, K. Hasegawa, H. Saito, Y. Noda, H. Okubo

2012.3.9

Propagation Process of Impulse Surface Flashover on Alumina Dielectrics in Vacuum International conference

Y. Nakano, H. Kojima, N. Hayakawa, K. Tsuchiya, H. Okubo

International Symposium on EcoTopia Science 2011

Partial Discharge in Vacuum on Insulator Surface under AC Voltage Application International conference

H. Kojima, K. Aoki, N. Hayakawa, M. Hanai, M. Homma, T. Shioiri, H. Okubo

1st International Conference on Electric Power Equipment - Switching Technology 2011.10.25 China Electrotechnical Society and Chinese Society for Electrical Engineering

Event date： 2011.10

Language：English Presentation type：Oral presentation (general)

Venue：Xi’an Country：China

In high voltage vacuum apparatus, e.g. vacuum circuit breaker, a partial discharge phenomenon, which is not breakdown but has a potential to lead breakdown, is observed under AC voltage application. We investigate the partial discharge along an insulator surface in vacuum under AC voltage application by the measurement of the charging and the light emission. Under sudden AC high voltage application, the partial discharge along the alumina surface occurred at the peak voltage of both polarities, but mainly at the negative polarity. The partial discharge was initiated near the rod electrode and spread out over the whole alumina surface. The partial discharge and subsequent charging behavior on the alumina surface under AC voltage application was verified to be dominated by the distortion of electric field due to not only the negative charges on the alumina surface but also the decrease phase of applied AC voltage. © 2011 IEEE.

DOI： 10.1109/ICEPE-ST.2011.6123044

Scopus

Surface Flashover Propagation Process on Alumina Dielectrics under Impulse Voltage Application in Vacuum International conference

H. Kojima, Y. Nakano, N. Hayakawa, K. Tsuchiya, H. Okubo

1st International Conference on Electric Power Equipment - Switching Technology 2011.10.26 China Electrotechnical Society and Chinese Society for Electrical Engineering

Event date： 2011.10

Language：English Presentation type：Oral presentation (general)

Venue：Xi’an Country：China

We investigated the mechanism of surface flashover on alumina dielectrics under impulse voltage application in vacuum in order to enhance the electrical insulation performance of vacuum insulated power equipment. Through electrical and optical simultaneous measurements, we discussed propagation process of the surface flashover on alumina dielectrics in vacuum. We changed the incident angle (θ) of electric lines of force to the alumina surface, i.e. parallel and perpendicular as the main parameter. The different propagation process of the surface flashover was found and discussed by the difference of charging process due to an electron flight distance. © 2011 IEEE.

DOI： 10.1109/ICEPE-ST.2011.6123046

Scopus

Impulse Breakdown Mechanism Based on Discharge Propagation Process under Non-uniform Electric Field in Air International conference

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

2011 IEEE Conference on Electrical Insulation and Dielectric Phenomena 2011.10.18 IEEE Dielectrics and Electrical Insulation Society

Event date： 2011.10

Language：English Presentation type：Poster presentation

Venue：Cancun Country：Mexico

In this paper, we aim to clarify the discharge mechanism leading to breakdown under non-uniform electric field in air, especially on the propagation process of discharge current channel. The discharge measurement was performed in a needle (φ1 mm)-plane electrode system with gap length g=15-100 mm in 0.1 MPa dry air under applying a positive impulse voltage. We observed discharge current waveform and fast-framing images of light emission with image intensifier controlled by a nanosecond pulse. We found out two types of breakdown mechanisms from streamer initiation to breakdown (BD); secondary streamer progress and leader progress. In addition, we investigated the transition region between both types of BD mechanism, focusing on the case of gap length (g=30 mm). Finally, we found that the secondary streamer propagation would dominae the formation process of the discharge channel and the mechanism leading to BD. Also, we found the criterion of impulse breakdown mechanism in air. © 2011 IEEE.

DOI： 10.1109/CEIDP.2011.6232712

Scopus

Other Link： https://www.webofscience.com/wos/woscc/full-record/WOS:000399725600128

Power Flow Control in Consideration of Apparatus Aging Distribution and Failure Rate by Intelligent Grid Management System (IGMS)

K. Wakaiki, K. Shinoda, H. Kojima, N. Hayakawa, M. Hanai, H. Okubo

2011.9.29