Faculty Profiles - KOJIMA Hiroki

Presentations -

Division display 381 - 400 of about 795 ／ All the affair displays >>

液体窒素の絶縁破壊電界におけるサイズ効果の圧力・温度依存性

西町誠一郎，小島寛樹，花井正広，早川直樹

電気学会放電/誘電・絶縁材料/高電圧合同研究会 2014.1.23 電気学会電/誘電・絶縁材料/高電圧技術委員会

Intelligent Grid Management System (IGMS) with Optimum Power Flow and Degradation Control of Power Apparatus International conference

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

International Symposium on EcoTopia Science 2013

Electrical Insulation Characteristics of Insulating Oil with Dispersed TiO₂ and ZnO Nanoparticles International conference

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

International Symposium on EcoTopia Science 2013

Spark Conditioning Effect on Multi-gap Electrode System in Vacuum International conference

Y. Otake, H. Kojima, N. Hayakawa, K. Hasegawa, H. Saito, M. Sakaki, H. Okubo

International Symposium on EcoTopia Science 2013

Initiation and Propagation Mechanism of Leader-type Breakdown in Air International conference

T. Kitamura, K. Hotta, H. Kojima, N. Hayakawa, K. Kobayashi, T. Kato, T. Rokunohe, H. Okubo

International Symposium on EcoTopia Science 2013

Electric Field Control for Gas Insulated Switchgear with Functionally Graded Materials (FGM) on Surface Conductivity International conference

J. Ishiguro, H. Kojima, M. Hanai, K. Kato, H. Okubo, N. Hayakawa

International Symposium on EcoTopia Science 2013

Influence of Needle Electrode Material and Shape on Electromagnetic Wave Radiation Characteristics of Partial Discharge in SF₆ Gas International conference

R. Mizuno, M. Hanai, H. Kojima, N. Hayakawa, M. Yoshida, H. Okubo

International Symposium on EcoTopia Science 2013

Current Limiting Characteristics of Superconducting Fault Current Limiting Cable (SFCLC) with Longitudinal Temperature Distribution International conference

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

International Symposium on EcoTopia Science 2013

Partial Discharge Inception Characteristics of Rectangular Wires for Inverter-fed Motors International conference

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

International Symposium on EcoTopia Science 2013

Inception Mechanism of Surface Flashover on Solid Insulator in Vacuum International conference

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

International Symposium on EcoTopia Science 2013

真空中における突発的電子放出に起因する沿面フラッシオーバメカニズム

中野裕介，小島寛樹，土屋賢治，早川直樹

電気学会放電/開閉保護/高電圧合同研究会 2013.11.20 電気学会放電/開閉保護/高電圧技術委員会

Conditioning Process of Multi-gap Electrode System with Cu-Cr Rod Electrode in Vacuum International conference

Y. Otake, H. Kojima, N. Hayakawa, K. Hasegawa, H. Saito, M. Sakaki, 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

In order to clarify the characteristics of spark conditioning carried out in parallel at several parts of electrodes, we studied conditioning process in a multi-gap electrode system with two rod-plane electrodes in vacuum. The rod material and gap distance of one gap was kept to Cu-Cr (d=5 mm) in some multi-gap electrodes. On the other hand, the rod material and gap distance of the other gap were varied. As a result, the number of breakdowns till conditioning saturation of Cu-Cr rod in the multi-gap electrode system was less than that in the single-gap electrode system. These results suggest that charge activity occurs between electrodes even at the gap without breakdown, which can also contribute to the conditioning effect. © 2013 IEEE.

DOI： 10.1109/ICEPE-ST.2013.6804375

Other Link： https://www.webofscience.com/wos/woscc/full-record/WOS:000355108400088

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

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

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

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

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

Inception and Expansion Process of Surface Flashover on Solid Dielectrics in Vacuum International conference

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

Surface discharge on solid insulator in vacuum, which is one of the most significant phenomena under high electric field, prevents vacuum circuit breaker and vacuum interrupter from applying to higher voltage level. To clarify the mechanism of surface flashover, we investigated the transiently-formed charge characteristics on alumina dielectrics in the development process of surface flashover, by using electrostatic probes behind alumina dielectrics and measuring the light emission image of flashover. As a result, we found out that charge distribution on the alumina dielectrics in the inception of surface flashover depends on the electron emission sites on the cathode and influences the expansion process of surface flashover in vacuum. © 2013 IEEE.

DOI： 10.1109/ICEPE-ST.2013.6804361

Other Link： https://www.webofscience.com/wos/woscc/full-record/WOS:000355108400074

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

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

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

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

　 PREV - NEXT 　