Faculty Profiles - KOJIMA Hiroki

Presentations -

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真空中スパークコンディショニング過程における突起生成と飽和

近藤史規，小島寛樹，福田英昭，榊正幸，早川直樹

令和元年度電気・電子・情報関係学会東海支部連合大会

誘電率/導電率傾斜機能材料（ε/σ-FGM）の作製と放電開始電圧向上効果の検証

宮崎勇作，小島寛樹，加藤克巳，満留博，柳瀬博雅，岡本健次，早川直樹

令和元年度電気・電子・情報関係学会東海支部連合大会

直流高電圧印加時における傾斜機能材料の電界緩和の時間依存性

伊豆淳宏，中根龍一，小島寛樹，加藤克巳，早川直樹

令和元年度電気・電子・情報関係学会東海支部連合大会

超高圧超電導ケーブルに向けたTyvek^®/PE/Tyvek^®およびPPLP^®の電気絶縁特性の圧力依存性

山上浩輝，小島寛樹，増田孝人，早川直樹

令和元年度電気・電子・情報関係学会東海支部連合大会

FGM絶縁スペーサの誘電率逆求解自動計算技術の開発とその検証

加藤克巳，小島寛樹，早川直樹，満留博，柳瀬博雅，岡本健次，大久保仁

令和元年電気学会電力・エネルギー部門大会

Fault Current Limitation Coordination of Multiple SFCLs in IEEE 14-Bus System International conference

N. Hayakawa, Y. Mori, H. Kojima

14th European Conference on Applied Superconductivity

Quench-induced Breakdown Characteristics of HTS Pancake Coil for Resistive SFCL International conference

N. Hayakawa, M. Mimbu, H. Kojima, S. Isojima, M. Kuwata

14th European Conference on Applied Superconductivity

Inverse Analysis of Permittivity Distribution of FGM (Functionally Graded Materials) Insulator in Gaseous Insulation System International conference

K. Kato, H. Kojima, N. Hayakawa, H. Mitsudome, H. Yanase, K. Okamoto, H. Okubo

21st International Symposium on High Voltage Engineering

Modeling of Channel Heating Breakdown in Dry Air International conference

H. Kojima, R. Asano, D. Komesu, J. Nukaga, T. Rokunohe, N. Hayakawa

21st International Symposium on High Voltage Engineering 2019.8.27 Budapest University of Technology

Event date： 2019.8

Language：English Presentation type：Poster presentation

Venue：Budapest Country：Hungary

In dry air with a relatively short gap length under non-uniform electric field, the channel heating breakdown mechanism becomes critical to the electrical insulation design of power apparatus. We have experimentally clarified that the input energy density into the discharge channel almost decides the occurrence of channel heating breakdown in dry air. This implies that the rise of the channel temperature due to Joule heating causes the rise of the channel conductivity and the current, leading to the breakdown. In this paper, we construct the discharge channel heating model by the resistance circuits in consideration of the temperature dependence of conductivity and the shape of discharge channel, and investigate the process leading to the channel heating breakdown in dry air. The electrode system in this model is needle-plane electrodes with the gap length of 15 mm based on our experiments. At first, we verified that the process of channel heating breakdown can be explained by the temperature dependence of conductivity by using the preliminary zero-dimensional model with uniform temperature distribution in the discharge channel. With the given applied voltage and initial temperature, the temporal evolution of current and conductivity was calculated. Calculation results revealed that the temporal evolution of conductivity and the time to breakdown were determined by not only the conductivity itself but also the temperature dependence of conductivity. Subsequently, we constructed the discharge channel heating model in consideration of the radial and axial temperature distribution. With the given initial temperature distribution, the calculated temporal evolution of current agreed with the measured current waveform just before breakdown. This result revealed that the temperature rise in the center column of discharge channel is the most important factor for the breakdown process. The calculated temporal evolution of the temperature distribution along the center axis revealed that the high temperature region would develop from the tip of the needle electrode toward the center of the gap. In addition, the calculated temporal evolution of the radial temperature distribution suggested that the temperature at the center column of the discharge channel would rise sharply just before breakdown. In conclusion, in the channel heating breakdown in dry air, we clarified the process of the current concentration on the center axis of the discharge channel, as well as the progress of high temperature region or high conductivity region in the axial direction from the tip of the needle electrode.

DOI： 10.1007/978-3-030-31680-8_41

Scopus

環境要因の相互作用を考慮したインバータサージ電圧下における部分放電開始電圧解析

梶武文，浅井洋光，野須敬弘，小島寛樹，早川直樹

電気学会放電・プラズマ・パルスパワー研究会 2019.5.16 電気学会放電・プラズマ・パルスパワー技術委員会