Faculty Profiles - KOJIMA Hiroki

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空気中不平等電界下における２次ストリーマ到達条件

堀田克輝，小島寛樹，早川直樹，柳田憲史，加藤達朗，六戸敏昭，大久保仁

平成24年度電気関係学会東海支部連合大会

Discrimination Technique of Streamer and Leader Type of Partial Discharge in SF₆ Gas Using UHF Method International conference

M. Hanai, K. Suzuki, R. Mizuno, H. Kojima, N. Hayakawa, H. Okubo

2012 IEEE International Conference on Condition Monitoring and Diagnosis 2012.9 School of Electrical Engineering and Informatics Bandung Institute of Technology, and Department of Electrical Engineering, Udayana University

Event date： 2012.9

Language：English Presentation type：Oral presentation (general)

Venue：Bali Country：Indonesia

The relationship between PD current pulse waveform at the PD source and radiated electromagnetic (EM) waveform is investigated, due to a metallic particle in SF6 gas. Leader discharge with the larger PD charge magnitude and the longer propagation length than those of streamer discharge can be an indicator of breakdown in SF6 gas. Simultaneous and synchronous measurement of PD current and EM signals in SF6 gas revealed that the streamer discharge and leader discharge could be discriminated in both time and frequency components, respectively. Compared with the streamer discharge in our experiment, the leader discharge is characterized by the longer rise/fall time. The partial discharge that has relatively little frequency components of 1500 MHz with electromagnetic waves can be presumed a leader discharge. This means that by applying the new technique, the streamer and leader types of PD in SF6 gas can be discriminated in UHF detecting system. © 2012 IEEE.

DOI： 10.1109/CMD.2012.6416437

Scopus

Other Link： https://www.webofscience.com/wos/woscc/full-record/WOS:000316544800071

Optimum Power Flow Control Based on Power Apparatus Diagnosis by Intelligent Grid Management System (IGMS) International conference

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

Event date： 2012.9

Language：English Presentation type：Oral presentation (general)

Venue：Bali Country：Indonesia

Transmission and distribution (T&D) system comprises a lot of aged apparatus, which may cause the decrease of the reliability owing to their deterioration. In order to maintain the high efficiency and high quality of T&D system, the authors have proposed 'Intelligent Grid Management System (IGMS)', which provides the optimum maintenance strategy and optimum power flow control. IGMS evaluates all of the events occurring in the T&D system as the cost. IGMS optimizes the power flow routes based on the failure risk, T&D loss, overload operation, life estimation of power apparatus, customer outage and so on. The impact of individual apparatus failure affects a whole T&D system performance such as blackout and secondary failure. The failure risk is also evaluated as cost by the product of the impact of the individual failure and the failure rate estimated by the condition monitoring diagnosis results of power apparatus. In this paper, the optimum power flow control based on the real-time diagnosis results of power apparatus is discussed. © 2012 IEEE.

DOI： 10.1109/CMD.2012.6416205

Scopus

Other Link： https://www.webofscience.com/wos/woscc/full-record/WOS:000316544800132

Optimum Maintenance Plan of Electric Power Apparatus in Consideration of Maintenance History by Intelligent Grid Management System (IGMS) International conference

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

Event date： 2012.9

Language：English Presentation type：Oral presentation (general)

Venue：Bali Country：Indonesia

Transmission and distribution (T&D) systemsare comprised of many aging apparatus, which impede the reliability and quality of the system. In order to maintain the high reliability and high quality of the T&D system, the authors have proposed 'Intelligent Grid Management System (IGMS)', which provides optimum maintenance strategy and optimum power flow control. In this paper, the optimum maintenance method and timing of the power apparatus in consideration of their maintenance history is discussed. The efficacy of the maintenance affects not only the performance at that time, but also the subsequent deterioration tendencies. The advanced IGMS with the consideration of the maintenance history is introduced to a T&D system model, and an optimum maintenance plan which minimizes the total cost in long-term perspective is derived. © 2012 IEEE.

DOI： 10.1109/CMD.2012.6416195

Scopus

Other Link： https://www.webofscience.com/wos/woscc/full-record/WOS:000316544800124

真空中におけるインパルス沿面放電の前駆発光特性

中野裕介，小島寛樹，早川直樹，土屋賢治，大久保仁

平成24年電気学会基礎・材料・共通部門大会

真空中のセラミック表面の発光開始電圧に与える電極表面粗さの影響

浅利直紀，塩入哲，佐藤純一，本間三孝，小島寛樹，花井正広，早川直樹，大久保仁

平成24年電気学会基礎・材料・共通部門大会

Streamer Development Mechanism under Non-uniform Electric Field in Air International conference

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

2012 International Conference on High Voltage Engineering and Application 2012.9.19 Chongqing Unviersity, Shanghai Jiaotong University, Mississippi State University

Event date： 2012.9

Language：English Presentation type：Oral presentation (general)

Venue：Shanghai Country：China

We discussed the development mechanism of the streamer channel leading to breakdown in a short air gap, by using an ultra-high speed measuring system. We clarified that the initiation of the secondary streamer leading to breakdown is attributed to an electron injection from the grounded plane electrode to the residual channel made by the primary streamer. In addition, by selective measurement of the discharge current waveform of single streamer channel leading to breakdown, the breakdown was verified to be dominated by the development of the secondary streamer and the subsequent Joule heating process focusing on the single streamer channel. © 2012 IEEE.

DOI： 10.1109/ICHVE.2012.6357036

Scopus

UHF電磁波の二周波数同時測定によるGIS部分放電診断

吉田昌展，小島寛樹，早川直樹，花井正広，大久保仁

平成24年電気学会電力・エネルギー部門大会

超電導電力機器におけるサブクール液体窒素の電気絶縁性能

西町誠一郎，小島寛樹，早川直樹，花井正広，大久保仁

平成24年電気学会電力・エネルギー部門大会

超電導限流ケーブル（SFCLC）の運転温度を考慮した限流特性の評価

大澤岳士，小島寛樹，早川直樹，花井正広，大久保仁

平成24年電気学会電力・エネルギー部門大会

空気中不平等電界下におけるインパルス絶縁破壊メカニズムの類別

堀田克輝，小島寛樹，早川直樹，柳田憲史，加藤達朗，六戸敏昭，大久保仁

平成24年電気学会電力・エネルギー部門大会

SF₆ガス中不平等電界下における部分放電形態とUHF電磁波特性

水野龍之介，吉田昌展，小島寛樹，早川直樹，花井正広，大久保仁

平成24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）による機器の更新時期を考慮した最適潮流制御

篠田康生，小島寛樹，早川直樹，花井正広，大久保仁

平成24年電気学会電力・エネルギー部門大会

部分放電メカニズムに基づくGIS中金属異物形状同定手法

小島寛樹，鈴木隆文，早川直樹，花井正広，大久保仁

平成24年電気学会電力・エネルギー部門大会

Conditioning Characteristics of Multi-Gap Electrode System in Vacuum International conference

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

25th International Symposium on Discharges and Electrical Insulation in Vacuum 2012.9.3 Institute of High Current Electronics, Siberian Branch of the Russian Academy of Sciences

Event date： 2012.9

Language：English Presentation type：Oral presentation (general)

Venue：Tomsk Country：Russian Federation

In order to clarify the characteristics of spark conditioning carried out in parallel at several parts of electrodes, we carried out conditioning experiment to use a multi-gap electrode system with multi-rod electrodes. As a result, we found that 50% breakdown voltage after conditioning saturation differed in the multi-gap electrode system from in a single gap electrode system. In addition, we found the different process to enhance the breakdown voltage in each electrode, by comparison to the single gap electrode system. © 2012 IEEE.

DOI： 10.1109/DEIV.2012.6412439

Scopus

Other Link： https://www.webofscience.com/wos/woscc/full-record/WOS:000315985400006

Development Process of Impulse Surface Discharge in Vacuum International conference

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

25th International Symposium on Discharges and Electrical Insulation in Vacuum 2012.9.4 Institute of High Current Electronics, Siberian Branch of the Russian Academy of Sciences

Event date： 2012.9

Language：English Presentation type：Poster presentation

Venue：Tomsk Country：Russian Federation

We investigated the charge activity on alumina dielectrics in the development process of impulse surface discharge in vacuum. We clarified the charge activity in pre-discharge stage by ultra-high speed and high sensitivity measurement. We also measured the fast-framing images of surface flashover propagation synchronously with current waveforms. We found that the charge activities are classified into three stages, i.e. (I) pre-discharge, (II) surface flashover initiation, and (III) expansion, in the development process of surface discharge in vacuum. © 2012 IEEE.

DOI： 10.1109/DEIV.2012.6412467

Scopus

Other Link： https://www.webofscience.com/wos/woscc/full-record/WOS:000315985400034

Charge Behavior and Partial Discharge Characteristics on Alumina Insulation under AC Voltage Application in Vacuum International conference

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

25th International Symposium on Discharges and Electrical Insulation in Vacuum 2012.9.4 Institute of High Current Electronics, Siberian Branch of the Russian Academy of Sciences

Event date： 2012.9

Language：English Presentation type：Poster presentation

Venue：Tomsk Country：Russian Federation

The charge behavior and partial discharge characteristics, which is not breakdown but has a potential to lead breakdown, at solid-composite system in vacuum can be a critical issue to be investigated, under ac operating 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 the negative polarity. The partial discharge was initiated near the rod electrode and spread out over the whole alumina surface. By the analysis of electric field, 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 the negative charges accumulated on the alumina surface, and this distortion occurs at the period of decrease of negative applied voltage. © 2012 IEEE.

DOI： 10.1109/DEIV.2012.6412452

Scopus

Other Link： https://www.webofscience.com/wos/woscc/full-record/WOS:000315985400019

Introduction Effect of Superconducting Power Flow Controller and Fault Current Limiter (SPFCL) in an Electric Power System

N. Hayakawa, X. Mao, H. Kojima, M. Hanai, N. Kashima, S. Nagaya, S. Sugimoto, H. Okubo

2012.6.22

Charge Behavior in Palm Fatty Acid Ester Oil (PFAE) / Pressboard Composite Insulation System under Voltage Application International conference

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

2012 IEEE International Symposium on Electrical Insulation 2012.6.12 IEEE Dielectrics and Electrical Insulation Society

Event date： 2012.6

Language：English Presentation type：Oral presentation (general)

Venue：San Juan Country：Puerto Rico

Palm Fatty Acid Ester Oil (PFAE) is one of the most promising environment-friendly biodegradable insulating oils for transformers. PFAE has significant advantages compared to other vegetable origin insulating oils and mineral oil, e.g. not only good insulation performance, high permittivity and high moisture tolerance, but also excellent cooling ability due to low kinematic viscosity, high thermal and chemical stability and high productivity. However, since the molecular content of PFAE is quite different from mineral oil, the fundamental charge behavior in PFAE has not been clarified yet. To clarify the temporal and spatial charge behavior in PFAE, we directly measured the electric field in oil duct model with PFAE / pressboard (PB) composite insulation system under dc voltage application and charged flow condition by using Kerr electrooptic field measurement technique. By the comparison of electric field and charge behavior characteristics with fresh and degraded mineral oil, we revealed that the essential mechanism of charge behavior is similar, but the difference in temporal and spatial characteristics is attributed to the higher intrinsic ion density and higher permittivity of PFAE than that of mineral oil.

DOI： 10.1109/ELINSL.2012.6251502

Scopus

CiNii Research

Other Link： https://www.webofscience.com/wos/woscc/full-record/WOS:000309221800085

真空中平行平板電極系におけるインパルスコンディショニングのギャップ長依存性

西村亮岐，小島寛樹，早川直樹，大久保仁

平成24年電気学会全国大会

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