Faculty Profiles - KOJIMA Hiroki

Presentations -

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Partial Discharge Characteristics and Mechanisms in Consideration of Charge Behavior on Alumina Dielectrics under AC Voltage in Vacuum International conference

H. Kojima, M. Ishida, N. Hayakawa, M. Hanai, J. Ikeda, T. Shioiri, H. Okubo

2nd International Conference on Electric Power Equipment - Switching Technology 2013.10.22 Nagoya University

Event date： 2013.10

Language：English Presentation type：Oral presentation (general)

Venue：Matsue Country：Japan

Partial discharge phenomenon, which is not breakdown but has a potential to lead breakdown, is sometimes observed under AC operating voltage application in vacuum. We aim to investigate the partial discharge on the insulator surface in vacuum by the measurement of charge behavior and light emission. The surface charge distribution reached a quasi-stationary state by repetition of the partial discharge. However, a sudden drastic change of surface charge distribution to another quasi-stationary state was also observed. This behavior could be explained by the sudden increase/decrease of electron emission from the cathode and the distribution of electric field due to the increase/decrease of accumulated surface charge by repetitive partial discharge under ac voltage. © 2013 IEEE.

DOI： 10.1109/ICEPE-ST.2013.6804363

Scopus

Other Link： https://www.webofscience.com/wos/woscc/full-record/WOS:000355108400076

Development of Discharge Inception Simulator Considering Environmental Factors Using Advection-Diffusion Model International conference

A. Ohtake, K. Kobayashi, T. Kato, N. Yanagita, T. Rokunohe, H. Kojima, N. Hayakawa, H. Okubo

2nd International Conference on Electric Power Equipment - Switching Technology 2013.10.21 Nagoya University

Event date： 2013.10

Language：English Presentation type：Oral presentation (general)

Venue：Matsue Country：Japan

Insulation design with discharge simulation based on physical phenomena is used in designing electrical instruments to facilitate their miniaturization and obtain high insulation reliability. We developed a model to calculate partial discharge inception in a non-uniform air gap by considering how environmental factors, especially humidity, affect insulation performance. We upgraded the calculation model that built in the distribution of negative ion density using the amount of moisture on the electrodes. As a result, we can estimate the discharge inception voltage with high accuracy. Additionally, we attempted to extend the simulator for three-dimensional creep analysis. © 2013 IEEE.

DOI： 10.1109/ICEPE-ST.2013.6804308

Scopus

Other Link： https://www.webofscience.com/wos/woscc/full-record/WOS:000355108400021

Dependence of TiO₂ and ZnO Nanoparticle Concentration on Electrical Insulation Characteristics of Insulating Oil International conference

M. Hanai, S. Hosomi, H. Kojima, N. Hayakawa, H. Okubo

2013 IEEE Conference on Electrical Insulation and Dielectric Phenomena 2013.10.22 IEEE Dielectrics and Electrical Insulation Society

Event date： 2013.10

Language：English Presentation type：Poster presentation

Venue：Shenzhen Country：China

This paper presents that mineral oil and linear alkylbenzene with dispersed metal oxide nanoparticles were investigated to clarify the effect of nanoparticles on AC breakdown strength and relative permittivity characteristics. The materials of nanoparticles were selected at TiO2 (crystal structure of anatase and rutile) and ZnO. The nanoparticle concentrations of samples were prepared varying from 0 to 0.5 vol% into mineral oil or linear alkylbenzene by ultrasonic dispersion. AC (60 Hz) breakdown test was performed in a sphere-sphere electrode (diameter φ=12.5 mm, stainless steel) with gap length 2.0 mm, and also relative permittivity was measured at 60 Hz at room temperature. The breakdown strength increased by about 5 to 15% with the addition of nanoparticles. Relative permittivity increased with the addition of nanoparticles. With some combinations of insulating oil and nanoparticle, the measured relative permittivity agreed with the calculation with the random arranged model. But there are some combinations that the measured relative permittivity and the calculated one aren't coincident. These instructions give basic guidelines for illuminating their insulating characteristics. © 2013 IEEE.

DOI： 10.1109/CEIDP.2013.6748164

Scopus

Other Link： https://www.webofscience.com/wos/woscc/full-record/WOS:000360957000191

Transition of Partial Discharge Inception Voltage under High Humidity for Enameled Rectangular Wires International conference

T. Wakimoto, H. Kojima, M. Hanai, N. Hayakawa

2013 IEEE Conference on Electrical Insulation and Dielectric Phenomena 2013.10.23 IEEE Dielectrics and Electrical Insulation Society

Event date： 2013.10

Language：English Presentation type：Poster presentation

Venue：Shenzhen Country：China

In recent years, the miniaturization and greater power output of motors for EVs and HEVs have led to the higher drive voltages and the increased adoption of rectangular wire in coils (higher volume ratio). In order to ensure that the motor is electrically insulated, it is necessary to restrict partial discharges between coil wires, and to do this, it is important to reduce the potential difference between wires resulting from the operation of the inverter and to ensure that the coil wire has the proper coating thickness. However, the measurement of partial discharges between wires results in variability in the measured values depending on the environment and methods, which is a problem for the stringently controlled design of motor insulation. To clarify the factors affecting the partial discharge inception voltage (PDIV) between wires as well as the mechanism, the effect of ambient humidity, pre-discharge conditions on the PDIV between wires was analyzed using rectangular wire with a coating thickness of 40 μm and 160 μm. As a result, it was confirmed that when a pre-discharge is performed in a high-humidity environment, transient characteristics were displayed in which PDIV momentarily decreased and then increased. We performed discharge observations and electric field analysis. The results showed that in high-humidity environments, the pre-discharge causes moisture to adhere to the coating surface, resulting in the increase in surface conductivity, which influences the electric field strength in the air gap. © 2013 IEEE.

DOI： 10.1109/CEIDP.2013.6748317

Scopus

Other Link： https://www.webofscience.com/wos/woscc/full-record/WOS:000360957000289

無鉄心超電導変圧器を用いた超電導限流/潮流制御装置（SPFCL）の限流特性

Cheng Wai Tatt，西町誠一郎，小島寛樹，花井正広，鹿島直二，長屋重夫，杉本重行，早川直樹

平成25年度電気関係学会東海支部連合大会

高湿度下のプレ放電がエナメル平角電線の部分放電開始電圧特性に与える影響

脇本亨，小島寛樹，花井正広，早川直樹

平成25年度電気関係学会東海支部連合大会

導電率傾斜機能材料（FGM）適用によるGISスペーサの電界制御

石黒純也，小島寛樹，花井正広，加藤克巳，早川直樹

平成25年度電気関係学会東海支部連合大会

サブクール液体窒素の絶縁破壊メカニズムおよびサイズ効果

西町誠一郎，小島寛樹，花井正広，早川直樹

平成25年度電気関係学会東海支部連合大会

TiO₂およびZnOナノ粒子分散による鉱油の電気絶縁特性向上

佐藤広治，小島寛樹，花井正広，早川直樹

平成25年度電気関係学会東海支部連合大会

真空中棒－平板電極系におけるスパークコンディショニング特性の放電電荷量依存性

大竹泰智，小島寛樹，長谷川光佑，斉藤仁，榊正幸，早川直樹

平成25年度電気関係学会東海支部連合大会

空気中不平等電界下におけるリーダ型絶縁破壊特性

北村卓也，小島寛樹，小林金也，加藤達朗，六戸敏昭，早川直樹

平成25年度電気関係学会東海支部連合大会

真空中沿面フラッシオーバの過渡帯電量と進展特性

中野裕介，小島寛樹，土屋賢治，早川直樹

平成25年度電気関係学会東海支部連合大会

IGMS（Intelligent Grid Management System）による電力機器の最適保守計画の導出精度

深谷皇紀，小島寛樹，花井正広，早川直樹

平成25年度電気関係学会東海支部連合大会

電磁波伝搬特性に基づくUHF法によるSF₆ガス中/空気中部分放電の識別

水野龍之介，小島寛樹，花井正広，吉田昌展，早川直樹

平成25年度電気関係学会東海支部連合大会

超電導限流ケーブル（SFCLC）の限流特性におけるケーブル入口温度依存性

大澤岳士，小島寛樹，花井正広，早川直樹

平成25年度電気関係学会東海支部連合大会

Influence of Longitudinal Temperature Distribution on Current Limiting Function of Superconducting Fault Current Limiting Cable (SFCLC) International conference

H. Kojima, T. Osawa, N. Hayakawa, M. Hanai, H. Okubo

11th European Conference on Applied Superconductivity

エナメル平角電線における高湿度下の部分放電開始電圧推移

脇本亨，花井正広，小島寛樹，早川直樹

平成25年電気学会基礎・材料・共通部門大会

真空中沿面フラッシオーバ開始時の放出電流特性

中野裕介，小島寛樹，土屋賢治，大久保仁，早川直樹

平成25年電気学会基礎・材料・共通部門大会

誘電率傾斜機能材料（FGM）によるGISスペーサ電界制御のフィラー粒径分布依存性

石黒純也，小島寛樹，花井正広，加藤克巳，大久保仁，早川直樹

平成25年電気学会基礎・材料・共通部門大会

空気中2次ストリーマ進展に及ぼす背後電界の影響

北村卓也，小島寛樹，早川直樹，小林金也，加藤達朗，六戸敏昭，大久保仁

平成25年電気学会基礎・材料・共通部門大会

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<KOJIMA Hiroki>

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