Updated on 2024/05/16

写真a

 
KOJIMA Hiroki
 
Organization
Graduate School of Engineering Electrical Engineering 1 Associate professor
Graduate School
Graduate School of Engineering
Undergraduate School
School of Engineering Electrical Engineering, Electronics, and Information Engineering
Title
Associate professor
Contact information
メールアドレス
External link

Degree 3

  1. Doctor (Engineering) ( 2004.3   Nagoya University ) 

  2. Master (Engineering) ( 2000.3   Nagoya University ) 

  3. Bachelor (Engineering) ( 1998.3   Nagoya University ) 

Research Interests 4

  1. High voltage

  2. Breakdown

  3. Discharge

  4. Electrical insulation

Research Areas 1

  1. Manufacturing Technology (Mechanical Engineering, Electrical and Electronic Engineering, Chemical Engineering) / Power engineering

Current Research Project and SDGs 3

  1. 環境に調和した次世代電力機器に関する研究

  2. 高柔軟な電気エネルギーシステム・設備のマネジメント技術に関する研究

  3. 超電導電力機器・システムに関する研究

Research History 5

  1. Nagoya University   Graduate School of Engineering   Associate professor

    2014.4

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    Country:Japan

  2. Nagoya University   EcoTopia Science Institute   Endowed chair associate professor

    2010.4 - 2014.3

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    Country:Japan

  3. Nagoya University   EcoTopia Science Institute   Endowed chair assistant professor

    2007.4 - 2010.3

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    Country:Japan

  4. Nagoya University   EcoTopia Science Institute   Assistant

    2005.4 - 2007.3

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    Country:Japan

  5. Nagoya University   EcoTopia Science Institute   Assistant

    2004.4 - 2005.3

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    Country:Japan

Education 3

  1. Nagoya University   Graduate School of Engineering   Department of Energy Engineering and Science

    2000.4 - 2004.3

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    Country: Japan

  2. Nagoya University   Graduate School of Engineering   Department of Energy Engineering and Science

    1998.4 - 2000.3

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    Country: Japan

  3. Nagoya University   School of Engineering   Department of Electrical Engineering

    1994.4 - 1998.3

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    Country: Japan

Committee Memberships 73

  1. 電気学会 次世代パワーエレクトロニクスと共に発展するインバータ駆動回転機の絶縁技術調査専門委員会   委員  

    2024.6 - 2027.5   

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    Committee type:Academic society

  2. 電気学会 令和6年基礎・材料・共通部門大会企画セッション委員会   委員  

    2024.1 - 2024.5   

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    Committee type:Academic society

  3. ISH2025 実行委員会   幹事  

    2023.4 - 2026.3   

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    Committee type:Academic society

  4. 中部電力 電力技術研究会 系統運用専門部会   専門委員  

    2023.4 - 2025.3   

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    Committee type:Other

  5. APSPT-13 Organizing Committee   Chair person  

    2023 - 2024   

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    Committee type:Academic society

  6. 電気学会 変圧器の保守・更新技術の最新動向調査専門委員会   委員  

    2022.10 - 2025.9   

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    Committee type:Academic society

  7. 電気学会放電・プラズマ・パルスパワー技術委員会   委員長  

    2022.6 - 2025.3   

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    Committee type:Academic society

  8. 経済産業省産業構造審議会   臨時委員  

    2021.7 - 2025.7   

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    Committee type:Government

    保安・消費生活用製品安全分科会電力安全小委員会電気設備自然災害等対策WG

  9. 電気学会 論文委員会(A2グループ)   委員  

    2021.4   

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    Committee type:Academic society

  10. 電気学会高電圧技術委員会   1号委員  

    2021.4 - 2027.3   

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    Committee type:Academic society

  11. 電気技術者試験センター   試験員  

    2021.4 - 2023.3   

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    Committee type:Other

  12. 電気学会 変圧器・リアクトルの騒音対策に関する最新動向調査専門委員会   委員  

    2019.10 - 2022.9   

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    Committee type:Academic society

  13. パワーアカデミー大学検討委員会 若手教員/研究者支援WG   主査  

    2018.4   

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    Committee type:Academic society

  14. 公益財団法人名古屋産業科学研究所   非常勤所員  

    2017.9 - 2025.3   

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    Committee type:Other

  15. CIGRE SC C4 国内分科会   委員  

    2014.1   

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    Committee type:Academic society

  16. 電気学会 令和5年基礎・材料・共通部門大会実行委員会   委員  

    2023.1 - 2023.12   

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    Committee type:Academic society

  17. 電気学会 令和5年基礎・材料・共通部門大会企画セッション委員会   委員  

    2023.1 - 2023.5   

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    Committee type:Academic society

  18. 令和5年電気学会全国大会実行委員会   幹事  

    2022.6 - 2023.6   

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    Committee type:Academic society

  19. 電気学会放電・プラズマ・パルスパワー技術委員会   副委員長  

    2022.4 - 2022.5   

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    Committee type:Academic society

  20. ISPlasma2023/IC-PLANTS2023 Organizing Committee   Vice-chair person  

    2022 - 2023   

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    Committee type:Academic society

  21. CMD2022組織委員会   委員  

    2021.4 - 2023.3   

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    Committee type:Academic society

  22. ISDEIV2023現地実行委員会   委員  

    2021.3 - 2023.12   

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    Committee type:Academic society

  23. 独立行政法人日本学術振興会   科学研究費委員会専門委員  

    2020.12 - 2021.11   

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    Committee type:Government

  24. 電気協同研究会 架空送電設備の絶縁設計調査専門委員会   専門委員  

    2020.10 - 2023.9   

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    Committee type:Academic society

  25. 電気学会ガス絶縁開閉装置の環境負荷低減への技術動向調査専門委員会   委員  

    2020.10 - 2023.3   

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    Committee type:Academic society

  26. 電気学会 論文委員会(A2グループ)   主査  

    2020.4 - 2021.3   

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    Committee type:Academic society

  27. 電気学会 基礎・材料・共通部門編修委員会   委員  

    2020.4 - 2021.3   

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    Committee type:Academic society

  28. ISDEIV2022現地実行委員会   委員  

    2020.3 - 2022.12   

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    Committee type:Academic society

  29. 独立行政法人日本学術振興会   科学研究費委員会専門委員  

    2019.12 - 2020.11   

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    Committee type:Government

  30. 電気学会 絶縁協調標準特別委員会   委員  

    2019.11 - 2023.10   

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    Committee type:Academic society

  31. 電気学会放電・プラズマ・パルスパワー技術委員会   幹事  

    2019.1 - 2022.3   

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    Committee type:Academic society

  32. 第50回電気電子絶縁材料システムシンポジウム現地実行委員会   委員  

    2019   

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    Committee type:Academic society

  33. ICEPE-ST2019 現地実行委員会(LOC)   委員  

    2018.1 - 2019.12   

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    Committee type:Academic society

  34. NEDO研究評価委員会「次世代洋上直流送電システム開発事業」分科会   NEDO技術委員  

    2017.5 - 2019.3   

  35. 電気学会 ガス絶縁開閉装置(GIS)に関連する最新規格と今後の技術動向調査専門委員会   委員  

    2017.4 - 2019.3   

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    Committee type:Academic society

  36. 電気学会 変圧器の機能・性能の多様化に関する最新動向調査専門委員会   委員  

    2016.10 - 2019.9   

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    Committee type:Academic society

  37. 電気学会 編修専門第1部会   委員  

    2016.4 - 2019.3   

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    Committee type:Academic society

  38. 電気学会 高電圧電気絶縁技術の歴史調査専門委員会   幹事  

    2016.4 - 2018.3   

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    Committee type:Academic society

  39. Organizing committee of IWHV & JK 2016   Member  

    2016   

  40. GD2016組織委員会   委員  

    2015.10 - 2017.3   

  41. GD2016実行委員会   幹事  

    2015.10 - 2017.3   

  42. GD2016現地委員会   幹事  

    2015.10 - 2017.3   

  43. 電気学会 論文委員会(A2グループ)   幹事  

    2015.4 - 2020.3   

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    Committee type:Academic society

  44. Steering Committee of 2015 KJ Joint Symposium on ED & HVE   member  

    2015   

  45. 電気学会 変圧器国内外規格の動向と比較調査専門委員会   委員  

    2014.10 - 2016.9   

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    Committee type:Academic society

  46. 平成27年電気学会電力・エネルギー部門大会実行委員会   幹事  

    2014.10 - 2015.9   

  47. 電気学会 ガス絶縁開閉装置(GIS)標準特別委員会   委員  

    2014.8 - 2016.7   

  48. 電気学会 次世代電力システムに向けたガス絶縁開閉装置へ要求される技術動向調査専門委員会   委員  

    2014.4 - 2016.9   

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    Committee type:Academic society

  49. 電気学会広報委員会   委員  

    2013.5 - 2014.5   

  50. 電気学会創立125周年記念事業委員会   委員  

    2013.5 - 2014.5   

  51. 平成25年度電気関係学会東海支部連合大会実行委員会   幹事  

    2013.4 - 2014.1   

  52. 平成25年度電気関係学会東海支部連合大会プログラム編集委員会   幹事  

    2013.4 - 2013.9   

  53. 平成25年度電気関係学会東海支部連合大会大会委員会   庶務幹事  

    2013.3 - 2014.2   

  54. 電気学会絶縁性液体の電気的・化学的挙動と製品適用技術調査専門委員会   委員  

    2012.10 - 2015.9   

  55. 電気学会変圧器解析における高度利用技術調査専門委員会   委員  

    2012.10 - 2014.9   

  56. 電気学会静止器技術委員会   1号委員  

    2012.7 - 2020.3   

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    Committee type:Academic society

  57. 電気学会放電技術委員会   幹事  

    2012.7 - 2018.12   

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    Committee type:Academic society

  58. 平成25年電気学会全国大会実行委員会   代表幹事  

    2012.6 - 2013.6   

  59. 平成25年電気学会全国大会小委員会   委員  

    2012.6 - 2013.6   

  60. 電気学会編修専門第3部会   委員  

    2012.5 - 2013.5   

  61. 電気学会創立125周年記念事業実行委員会   委員  

    2012.5 - 2013.5   

  62. 平成24年度電気関係学会東海支部連合大会実行委員会   委員  

    2012.4 - 2013.1   

  63. 平成24年度電気関係学会東海支部連合大会プログラム編集委員会   委員  

    2012.4 - 2012.9   

  64. ICEPE2013 現地実行委員会(LOC)   委員  

    2012.3 - 2014.3   

  65. 電気学会高経年GISに要求される適用技術の動向調査専門委員会   委員  

    2012.1 - 2013.12   

  66. パワーアカデミー大学検討委員会 若手教員/研究者支援WG   エリア代表幹事  

    2011.10 - 2018.3   

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    Committee type:Academic society

  67.   Member  

    2010.10 - 2012.9   

  68. イットリウム系超電導電力機器技術開発プロジェクトSMES試験法検討小委員会   委員  

    2010.6 - 2012.3   

  69. イットリウム系超電導電力機器技術開発プロジェクトSMESコイル検討小委員会   委員  

    2010.6 - 2011.3   

  70.   Member  

    2010.6 - 2010.9   

  71. CMD2010組織委員会   幹事補  

    2010.4 - 2011.2   

  72.   Assistant Secretary  

    2009.5 - 2012.4   

  73. CMD2010総務委員会   委員  

    2009.1 - 2011.2   

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Awards 6

  1. IEEJ Distinguished Paper Award

    2023.5   The Institute of Electrical Engineers of Japan   Partial Discharge Inception Voltage under Inverter Surge Voltage Considering Interactive Effects of Environmental Factors

    T. Kaji, H. Asai, T. Nozu, H. Kojima, N. Hayakawa

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    Award type:Honored in official journal of a scientific society, scientific journal  Country:Japan

  2. Best Paper Award CMD 2020

    2020.10   8th International Conference on Condition Monitoring and Diagnosis   Diagnosis of Discharge Pattern in Vacuum Interrupter by Shield Potential Measurement

    H. Kojima, T. Donen, T. Kimura, N. Hayakawa

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    Award type:Award from international society, conference, symposium, etc.  Country:Thailand

  3. パワーアカデミー萌芽研究優秀賞

    2019.3   パワーアカデミー   ガス絶縁開閉装置の絶縁診断高度化に向けた部分放電の電磁波放射メカニズムの解明

    小島寛樹

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    Award type:Award from publisher, newspaper, foundation, etc.  Country:Japan

  4. IEEJ Distinguished Paper Award

    2018.5   The Institute of Electrical Engineers of Japan   Improvement Mechanism of AC Breakdown Voltage of Insulating Oil with Dispersed Nanoparticles

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

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    Award type:Honored in official journal of a scientific society, scientific journal  Country:Japan

  5. IEEJ Distinguished Paper Award

    2012.5   The Institute of Electrical Engineers of Japan   Mechanism of Small Current Generation under Impulse Voltage Applications in Vacuum

    K. Aoki, H. Yasukawa, H. Kojima, M. Homma, T. Shioiri, H. Okubo

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    Award type:Honored in official journal of a scientific society, scientific journal  Country:Japan

  6. 電気学会論文発表賞(賞A)

    2007.9   電気学会   N#D2#DRO混合ガスによる絶縁特性のシナジズム効果

    小島寛樹

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    Award type:Award from Japanese society, conference, symposium, etc.  Country:Japan

    「N2O混合ガスによる絶縁特性のシナジズム効果」(平成18年電気学会電力・エネルギー部門大会)に対する受賞

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Papers 116

  1. Breakdown Charge Dependence of Counter Electrode Material Adhesion and Dielectric Strength after Spark Conditioning in Vacuum Reviewed International journal

    N. Kita, H. Kojima, N. Hayakawa, H. Fukuda, K. Yamamura, K. Nagatake

    IEEE Transactions on Dielectrics and Electrical Insulation   Vol. 30 ( 6 ) page: 2592 - 2598   2023.12

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:IEEE  

    Spark conditioning is an effective method of increasing the dielectric strength in vacuum. In this paper, we discuss the breakdown (BD) charge dependence of counter electrode material adhesion and dielectric strength after spark conditioning. We have applied a negative impulse voltage to a rod-plane electrode configuration with a cathode and an anode made of stainless steel (SUS) that is defined as SUS304 by JIS G 4303 or oxygen free high conductivity copper (Cu). The electrode system of cathode SUS and anode Cu is called SUS-Cu electrode system, and the electrode system of cathode Cu and anode SUS is called Cu-SUS electrode system. We have changed BD charge (QBD) in conditioning by changing the limiting resistance in the experimental circuit. As a result, in both cases of SUS-Cu and Cu-SUS electrode systems, the larger the QBD, the smaller the amount of the anode material adhered to the cathode surface. When QBD is large, the dielectric strength increases in SUS-Cu electrode system and decreases in Cu-SUS electrode system. From these results, when QBD is large, we consider that the conditioning characteristics are less likely to be dominated by the anode material, i.e. Cu in the case of SUS-Cu electrode system and SUS in the case of Cu-SUS electrode system. In other words, the decisive parameters such as QBD to maximize the dielectric strength may depend on the combination of electrode materials.

    DOI: 10.1109/TDEI.2023.3318887

    Web of Science

    Scopus

  2. Expected Lifetime Evaluation Method and Partial Discharge Progress Characteristics in Capacitor Voltage Transformer Reviewed

    Y. Nagaki, K. Hayashi, H. Kojima, M. Yoshida, A. Otani, N. Hayakawa

    IEEJ Transactions on Power and Energy   Vol. 143 ( 10 ) page: 559 - 566   2023.10

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    Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher:The Institute of Electrical Engineers of Japan  

    <p>Aged CVTs have been often used in substations, but the expected lifetime of CVTs is unclear, so that it is difficult to determine the appropriate renewal time. Therefore, in this paper, we focus on oil-impregnated paper capacitors inside CVTs and propose a concept to evaluate their expected lifetime based on the partial discharge (PD) progress characteristics. By using a fundamental oil-impregnated paper capacitor model, the PD progress characteristics were measured and discussed from electrical and optical aspects.</p>

    DOI: 10.1541/ieejpes.143.559

    Scopus

    CiNii Research

  3. Electric Field Grading and Discharge Inception Voltage Improvement on HVDC GIS/GIL Spacer with Permittivity and Conductivity Graded Materials (ε/σ-FGM) Reviewed International coauthorship International journal

    Rachmawati, H. Kojima, K. Kato, N. Zebouchi, N. Hayakawa

    IEEE Transactions on Dielectrics and Electrical Insulation   Vol. 29 ( 5 ) page: 1811 - 1817   2022.10

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:IEEE  

    Functionally graded materials (FGM) application with graded permittivity and conductivity is promising as an effective technique for electric field relaxation in SF<sub>6</sub> gas around HVDC GIS/GIL spacers. In order to approach the practical application of FGM to HVDC GIS/GIL spacers, this paper investigates the electric field reduction effect given by permittivity and conductivity graded materials (&#x03B5;/&#x03C3;-FGM) based on actual measured permittivity (&#x03B5;) characteristics of SrTiO<sub>3</sub>-filled epoxy composites and conductivity (&#x03C3;) characteristics of SiC-filled epoxy composites. In addition, theoretical discharge inception voltage (TDIV) of &#x03B5;/&#x03C3;-FGM spacer is calculated under standard lightning impulse (LI) voltage based on the Volume-Time theory. The results show that &#x03B5;/&#x03C3;-FGM spacer with grading to lower permittivity (GLP) (&#x03B5;<sub>r</sub> from 12.7 to 4) containing 0 to 26.9 vol% SrTiO<sub>3</sub>-filled epoxy composite and U-shaped graded conductivity containing 5 to 10 vol% SiC-filled epoxy composite is effective for electric field relaxation under DC steady state (DC-SS) and LI voltage where both resistive and capacitive fields present. It is attributed to the higher &#x03B5; and &#x03C3; of FGM spacer near the HV conductor/spacer interface. TDIV under LI voltage is also estimated to be 26% higher at 0.5 MPa-abs, compared to the conventional spacer without &#x03B5;/&#x03C3;-grading.

    DOI: 10.1109/TDEI.2022.3194489

    Web of Science

    Scopus

    Other Link: http://hdl.handle.net/2237/0002004749

  4. Melting and Generation of Micro-Protrusions on Cathode Surface during Spark Conditioning Process in Vacuum Reviewed International journal

    N. Kita, F. Kondo, H. Kojima, N. Hayakawa, H. Fukuda, K. Yamamura

    IEEE Transactions on Dielectrics and Electrical Insulation   Vol. 29 ( 3 ) page: 1160 - 1166   2022.6

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:IEEE  

    Spark conditioning is an effective method to increase the dielectric strength in vacuum by melting and removing micro-protrusions on the cathode surface. We aim to optimize the conditioning effect in vacuum for the application of vacuum circuit breakers (VCBs) to higher voltage levels. To obtain high breakdown (BD) voltage, the control of BD charge in the conditioning process is required. When a BD occurs, we have suggested that micro-protrusions can be generated on the cathode surface by particles from the anode. For the suitable control of BD charge, the meltability of generated micro-protrusions and their size are important. In this paper, we focus on the generation of micro-protrusions on the cathode surface in conditioning process. First, we conduct spark conditioning by repetitive impulse voltages of rod-plane electrodes made of OFHC Cu in a vacuum chamber with different BD charge. After that, we observe the surface of rod cathode with a digital microscope in order to count the number of visible protrusions and measure their radii. By considering the meltability of micro-protrusions, we quantitatively reveal the existence of residual protrusions that cannot be completely melted by BD. Next, we estimate the maximum size of generated micro-protrusions by BD charge. In consideration of the collision of ions into the anode accelerated by the anode sheath voltage, we estimate the meltable amount of anode material by the BD charge. We confirm that the radii of experimentally measured protrusions are close to the estimated ones. Moreover, we consider the difference in dielectric strength due to the difference in the initial surface condition of the electrodes. We clarify that the dielectric strength is improved by applying acid wash and heat treatment to the electrodes before conditioning, which can be optimized by the BD charge and the initial surface condition of the electrode.

    DOI: 10.1109/TDEI.2022.3173493

    Web of Science

    Scopus

    Other Link: http://hdl.handle.net/2237/0002004226

  5. Volume Effect of Dynamic Breakdown Strength in Liquid Nitrogen under Transient Bubble Disturbance for Resistive Superconducting Fault Current Limiters Reviewed International journal

    N. Hayakawa, Y. Mori, H. Kojima

    IEEE Transactions on Dielectrics and Electrical Insulation   Vol. 29 ( 1 ) page: 264 - 269   2022.2

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:IEEE  

    Liquid nitrogen (LN 2 ) is indispensable as the cooling and electrical insulating materials for high-temperature superconducting (HTS) power apparatus. Especially for the resistive superconducting fault current limiters (RSFCLs), a transient bubble disturbance in LN 2 is generated due to the quench of HTS materials, which may induce an electrical breakdown in LN 2 even under the rated voltage of RSFCL. We have been investigating not only the intrinsic breakdown characteristics of LN 2 under the steady-state operation, but also the dynamic breakdown characteristics of LN 2 under the fault current limiting operation of RSFCL. In this article, we investigate the heat flux and pressure dependence of the quench-induced dynamic breakdown characteristics of LN 2 by using an actual HTS conductor and a pancake coil model for RSFCL. In addition, the dynamic breakdown strength is discussed and systematized in terms of the volume effect of breakdown strength in LN 2 . A flowchart to estimate the intrinsic and dynamic breakdown strength in LN 2 is proposed toward the reliable and rational insulation design of RSFCL.

    DOI: 10.1109/TDEI.2022.3146564

    Web of Science

    Scopus

    Other Link: http://hdl.handle.net/2237/0002003092

  6. Breakdown Characteristics of Cone-type ε-FGM Spacer for Gas Insulated Switchgears Invited Reviewed

    Y. Miyazaki, H. Kojima, H. Masui, H. Mitsudome, H. Yanase, K. Okamoto, K. Watanabe, K. Kato, N. Hayakawa

    IEEJ Transactions on Fundamentals and Materials   Vol. 141 ( 10 ) page: 546 - 551   2021.10

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    <p>Gas insulated switchgears (GIS) are required to be downsized for the cost reduction, global warming mitigation and energy saving. For the downsizing of GIS, a novel electric field grading technique is highly expected. In order to solve this problem, we have been investigating the electric field control and relaxation technique by “functionally graded materials (FGM)” with spatial distribution of permittivity (ε-FGM) and/or conductivity (σ-FGM). In our previous works, post-type and truncated cone-type ε-FGM spacers were fabricated by “flexible mixture casting method” (FMC method). Compared with the conventional spacers (Uniform spacer) with a uniform permittivity distribution, the electric field grading effects of those ε-FGM spacers were simulated based on Volume-Time theory and verified by the measurement of their breakdown voltages.</p><p>In this paper, toward the application of ε-FGM to the actual GIS spacer, i.e. 30% reduction of spacer diameter or 50% reduction of cross section, we fabricated the 1/4-sized cone-type ε-FGM spacer. By grading the mixing ratio of SrTiO<sub>3</sub> (ε<sub>r</sub>=332) and SiO<sub>2</sub> (ε<sub>r</sub>=4) fillers in epoxy resin, a cone-type spacer with the diameter of 60 mm was fabricated by FMC method. The breakdown voltage of the ε-FGM spacer was measured in a tank filled with SF<sub>6</sub> gas at 0.5 MPa-abs under the negative standard lightning impulse voltage by the step-up method. The maximum breakdown voltage of ε-FGM spacer was verified to be higher by 23% than the Uniform spacer with the same configuration and size of the ε-FGM spacer, which was also consistent with the simulated value.</p>

    DOI: 10.1541/ieejfms.141.546

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  7. Alternative Test Method of Internal Arcing for Replacing SF6 by Air in SF6-Insulated Power Equipment Reviewed International journal

    M. Kotari, M. Iwata, H. Kojima, N. Hayakawa

    Engineering Research Express   Vol. 3 ( 3 ) page: 035005   2021.9

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    To develop an alternative test method of internal arcing for replacing sulfur hexafluoride (SF6) by air in SF6-insulated power equipment, it is important for the public safety to clarify the thermal effect of hot SF6 and air from the equipment on the surroundings. In this study, an analytical model for evaluating the incident heat energy on a metal plate by exhausted hot gas was developed and validated. SF6-air mixtures with a range of gas thermodynamic and transport properties up to 30,000Kwere modelled using computational fluid dynamics (CFD) to simulate the increase in pressure. The analytical results are investigated using the experimental results on SF6-air mixtures. Subsequently, a method of setting the test conditions for the internal arc testing in SF6-insulated power equipment, is proposed based on the analytical model. Using the mixture model, assuming an alternative arcing test for replacing SF6 by air in the SF6-insulated power equipment, the method of setting a current or the duration of current is demonstrated and verified. The results indicate that the current and duration of current can be set such that the incident heat energy on the metal plate by exhausted hot gas are approximately equalized. This study could establish an alternative test method of internal arc in SF6-insulated power equipment.

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  8. Dielectric Characteristics of Liquid Nitrogen/Synthetic Paper Composite Insulation System for Extra High Voltage HTS Cable Reviewed International journal

    N. Hayakawa, Y. Yamakami, T. Masuda, H. Kojima

    IEEE Transactions on Applied Superconductivity   Vol. 31 ( 5 ) page: 7700204   2021.8

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    For extra-high-voltage high-temperature superconducting (HTS) cables, not only high electrical insulation performance but also low dielectric loss is required. Therefore, we focus on a porous synthetic paper with lower dielectric loss, e.g., Tyvek polyethylene nonwoven fabric, than that of polypropylene laminated paper (PPLP), which has been used for a conventional HTS cable insulation system. In this paper, we compare partial discharge inception characteristics for different liquid nitrogen/synthetic paper composite insulation systems. The partial discharge inception electric field strength in the composite insulation system depends on the electric field strength in the porous area of synthetic paper.

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  9. Time Transition of Activated Conductivity Distribution in Air and Charge Accumulation in Air-solid Composite Insulation Systems under DC Partial Discharge Reviewed International journal

    R. Nakane, H. Kojima, N. Hayakawa

    IEEE Transactions on Dielectrics and Electrical Insulation   Vol. 28 ( 3 ) page: 822 - 828   2021.6

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    In this study, charge behavior in gas and on solid insulator due to DC partial discharge (DC-PD) is investigated by using needle-air-PMMA-plane electrode configuration under negative DC voltage. The time evolution of surface potential distributions on solid insulator is measured and compared with the simulation results taking into account the charge behavior in air, such as generation, recombination and motion of positive and negative ions. Especially, a novel transport equation model considering the source of charge carrier due to DC-PD is built. Consequently, in air-solid composite insulation systems under negative DC voltage application, the time transition of activated conductivity distribution in air by DC-PD contributing to the charge accumulation on PMMA surface is evaluated quantitatively. The activated conductivity in air is distributed in the range from 1.0 × 10^-9 to 3.0 × 10^-9 S/m under DC-PD, which is approximately 10 10 times higher than that in non-activated conductivity space by natural ionization. In addition, the activated conductivity distribution in air dominantly contributes to the charge accumulation process from initial state (DC-on) to DC steady-state. The activated conductivity is the crucial parameter for DC electrical insulation in case that charge behavior is activated in gas medium under DC-PD.

    DOI: 10.1109/TDEI.2021.009363

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  10. Development of Insulation System to Prevent Local Carbonization inside Stator Core of a Product Inverter-fed Motor Reviewed

    Y. Yoshitake, H. Kojima, Y. Kasai, S. Maruyama, H. Kojima, N. Hayakawa

    IEEJ Transactions on Fundamentals and Materials   Vol. 141 ( 4 ) page: 260 - 268   2021.4

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    <p>A new phenomenon, called “local carbonization” inside a stator core was detected as a unique precursor to fragility of the insulation sheets of inverter-fed motors, and the conditions for generation of this carbonization were investigated. A separated stator of a product inverter-fed motor was manufactured, and an evaluation system for simulating a steep surge voltage was constructed. Electrically and mechanically, the results of a parameter survey of insulation system were used to compare the constructed separated stator and element model, and the comparison revealed a correlation between carbonization of the product separated stator and element model. From the consideration of carbonization mechanism, leakage current was revealed to be the dominant design factor. Through quantifying their threshold of carbonization occurrence, insulation system to prevent the carbonization in steeper inverter surge was developed by parameter survey using element model and validation test by separated stator.</p>

    DOI: 10.1541/ieejfms.141.260

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  11. Electric Field Simulation of Permittivity and Conductivity Graded Materials (ε/σ-FGM) for HVDC GIS Spacers Reviewed International coauthorship International journal

    Rachmawati, H. Kojima, N. Hayakawa, K. Kato, N. Zebouchi

    IEEE Transactions on Dielectrics and Electrical Insulation   Vol. 28 ( 2 ) page: 736 - 744   2021.4

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    This paper discusses the application of the novel technology - functionally graded material (FGM), which combines both spatial permittivity (ε) and conductivity (σ) distributions with the aim to control the electric field around DC-GIS spacer. Some distribution types of ε and/or σ in the spacer bulk, such as U-type and graded to higher conductivity (GHC) are investigated through electric field simulation, in comparison to the uniform spacer with constant ε and σ distributions. The electric field relaxation effect of each distribution type of ε/σ-FGM under DC steady state, DC polarity reversal, DC-on, and lightning impulse voltage superimposed on DC steady state condition are obtained. The results show that ε/σ-FGM with U-type permittivity and GHC-type conductivity distribution of which low σ is applied near the high voltage side of the DC-GIS spacer is the most effective in reducing the maximum electric field under all stated conditions.

    DOI: 10.1109/TDEI.2020.009343

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  12. Reshaping of Micro-morphology Feature in Electrode Surface under Conditioning by Lightning Impulse Voltage in Vacuum Gaps Reviewed International coauthorship International journal

    H. Ma, G. Li, Z. Liu, Y. Geng, J. Wang, H. Kojima

    IEEE Transactions on Dielectrics and Electrical Insulation   Vol. 27 ( 6 ) page: 2056 - 2063   2020.12

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    The objective of this paper is to determine the reshaping of the micro-morphology feature in both the cathode and anode electrode surfaces after conditioning by lightning impulse voltage in vacuum gaps. Materials of the experimental rod-plane electrodes are Cu and stainless steel. The micro-morphology feature in the electrode surface is recorded by a 3D laser microscopy. Experimental results indicate that conditioning by the lightning impulse voltage reshaped the micro-morphology feature in both the cathode and anode electrode surfaces. The BD characteristics are closely related to the micro-morphology feature and roughness in the cathode surface after conditioning. Moreover, the conditioning process takes different effects in the cathode and anode surfaces. For cathode electrode, the main difference of the micro-morphology feature is in the distributing characteristics of the erosion regions. For anode electrode, there aree different patterns of the anodic conditioning mechanism of the micro-morphology feature. In the molten pattern, conditioning melted the anode surface and removed the micro-protrusions effectively. In the crater pattern, with the increasing BD voltage and energy, the material below the anode surface is heating, which is the cause of formation of the many craters in anode surface.

    DOI: 10.1109/TDEI.2020.008888

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  13. Partial Discharge Inception Voltage under Inverter Surge Voltage Considering Interactive Effects of Environmental Factors Reviewed

    T. Kaji, H. Asai, T. Nozu, H. Kojima, N. Hayakawa

    IEEJ Transactions on Fundamentals and Materials   Vol. 140 ( 7 ) page: 349 - 356   2020.7

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    <p>Effects of environmental factors on partial discharge inception voltage (PDIV) under inverter surge voltage was discussed with multiple regression analysis in this study. As the environmental factors, humidity, temperature, and pressure were taken into account. These factors can change in high-voltage motors used for actual vehicles. The PDIV under a surge voltage showed different changes from that under sinusoidal voltage due to variation of initial electron generation probability depending on environmental change. Our results revealed that humidity has a significant effect on the PDIV under surge voltage, and there are interactive effects between humidity and temperature, and humidity and pressure. We discussed the effect of humidity and these interactions in terms of the generation of initial electrons from the air and verified this by measuring the density of negative ions in the air.</p>

    DOI: 10.1541/ieejfms.140.349

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  14. Fault Current Limitation Coordination of Multiple SFCLs in IEEE 14-Bus Test System Reviewed International journal

    N. Hayakawa, Y. Mori, H. Kojima

    Journal of Physics: Conference Series   Vol. 1559 ( 1 ) page: 012138   2020.6

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    We have proposed the concept of "fault current limitation coordination" of multiple superconducting fault current limiters (SFCL) to be introduced in a future electric power grid. Using a simplified test system, the transients on fault current and internal phase angle of generators were analyzed by PSCAD/EMTDC and the modeling of resistive SFCL with a variable resistance as a function of both current and temperature at the recovery under load. In this paper, we extended the analyses to the fault current limitation coordination of multiple SFCLs in IEEE 14-bus test system. The effective coordination strategy on the introduction and operation of multiple SFCLs, e.g. introduction lines of SFCLs, operation parameters such as operating current, critical current and prospective fault current of each SFCL, was discussed and optimized for an arbitrary fault location in the test system.

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  15. Quench-induced Dynamic Breakdown Characteristics of HTS Pancake Coil Model for Resistive SFCL Reviewed International journal

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

    Journal of Physics: Conference Series   Vol. 1559 ( 1 ) page: 012100   2020.6

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    Quench-induced dynamic breakdown (BD) characteristics of LN2 under transient bubble disturbance at the quench of HTS tapes are crucial to the reliable and rational insulation design of resistive superconducting fault current limiters (RSFCL). We have been investigating the dynamic BD characteristics using a nichrome pancake coil model for RSFCL using bifilar nichrome tapes as a heater. In this paper, we fabricated an HTS pancake coil model for RSFCL using GdBCO tapes and discussed the dynamic BD characteristics as a function of heat flux generated from the actually quenched HTS tapes.

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  16. Elemental Consideration of Carbonization Phenomena in Inverter Fed Motor Reviewed

    Y. Yoshitake, H. Kojima, Y. Kasai, S. Maruyama, H. Kojima, N. Hayakawa

    IEEJ Transactions on Fundamentals and Materials   Vol. 140 ( 1 ) page: 40 - 47   2020.1

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    <p>“Carbonization” were detected as the precursor phenomena on the insulation burning of rotating machine, and we have studied the generation condition for higher <i>dV/dt</i> of the inverter surge. We built the experimental setup of elemental model, which could simulate the steeper surge from SiC device inverter and construct the stator insulation system inside the motor core to control the insulation sheets configuration. By revealing the quantitative conditions of the carbonization generation, we verified that the voltage to suppress the carbonization generation depended on the location of the mold release layer. Therefore, we developed the guideline of insulation design to prevent the carbonization for the steeper inverter surge.</p>

    DOI: 10.1541/ieejfms.140.40

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  17. Comparison of Permittivity Gradient in Resin Injected and Simulated Cone-Shaped Spacers Reviewed International journal

    T. Imai, M. Takeuchi, Y. Hoshina, H. Kojima, N. Hayakawa

    IEEE Transactions on Dielectrics and Electrical Insulation   Vol. 26 ( 5 ) page: 1678 - 1685   2019.10

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    Functionally graded materials are at the cutting edge of material technology. They will enable high efficiency and downsizing of apparatus leading to energy conservation in the power sector. Spacers with graded relative permittivity enable a decrease in the diameter of gas-insulated switchgears. Distribution of epoxy-based composite materials (resins) with different permittivities dominate the permittivity gradient in spacers. This paper compares resin injected spacers with simulation. High-permittivity resins, mixtures of high/low-permittivity resins at various mixing ratios, and low-permittivity resins were continuously injected to form spacers. In these spacers, both experiment and simulation showed similar tendencies of resin distribution and demonstrated permittivity gradients. Moreover, the high-permittivity resins were localized on the outlet sides rather than the inlet sides in both experimental and in simulation, and the simulation showed a stronger localization behavior than in the experiment.

    DOI: 10.1109/TDEI.2019.008240

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  18. Resin Injection Behavior in Process of Manufacturing Insulation Spacer with Permittivity Gradient Using Computational Fluid Dynamics Reviewed International journal

    T. Imai, Y. Hoshina, H. Kojima, N. Hayakawa

    IEEE Transactions on Dielectrics and Electrical Insulation   Vol. 26 ( 5 ) page: 1669 - 1677   2019.10

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    The advent of new technology for designing insulation materials with desired properties stimulates our interest in development of insulation spacers in gas-insulated switchgear (GIS). Tailoring of two kinds of epoxy-based composite materials (resins) with different relative permittivities enables development of insulation spacers with graded permittivity that decrease the diameter of a GIS tank. Computational fluid dynamics for the resin injection process based on the properties of resin mixtures at various mixing ratios between two resins with high/low relative permittivity enables us to estimate the injection behavior and distribution of resins in the manufacturing of insulation spacers. Simulation results demonstrated the gradient of resins in the insulation spacers by this resin injection method using two resins. In particular, the insulation spacer formed by two or four injection inlets have a more favorable distribution of resins than that achieved by one injection inlet.

    DOI: 10.1109/TDEI.2019.008239

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  19. Dynamic Breakdown Characteristics of Pancake Coil Model for Resistive-Type Superconducting Fault Current Limiters Reviewed International journal

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

    IEEE Transactions on Applied Superconductivity   Vol. 29 ( 5 ) page: 1 - 6   2019.8

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    Toward the reliable and rational insulation design of resistive-type superconducting fault current limiters (RSFCL), we have been investigating not only the intrinsic breakdown (BD) characteristics of liquid nitrogen (LN2) without bubbles but also the dynamic BD characteristics of LN2 under the transient bubble disturbance at the quench of RSFCL coils. We have so far used a fundamental model such as sphere-plane electrode system with quasi-uniform electric field. However, when RSFCL will be introduced in a future electric power network, a stack of pancake coils with non-uniform electric field will be adopted for the practical development of RSFCL. In this paper, we designed and fabricated a pancake coil model for RSFCL, and investigated the intrinsic and dynamic BD characteristics of the pancake coil models in LN2. Experimental results are discussed in terms of the volume effect of intrinsic and dynamic BD strength under non-uniform electric field.

    DOI: 10.1109/TASC.2019.2909200

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  20. Combined Effect of Temperature and Humidity on Partial Discharge Inception Voltage of Magnet Wires under Inverter-Surge Voltage Reviewed

    T. Kaji, H. Asai, H. Kojima, N. Hayakawa

    IEEJ Transactions on Fundamentals and Materials   Vol. 139 ( 1 ) page: 30 - 37   2019.1

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    <p>We investigated the combined effect of temperature and humidity on partial discharge inception voltage (PDIV) of magnet wires under repetitive surge-wave voltages. As the results, the PDIV increased as the temperature increased in the environment of uncontrolled humidity, which is peculiar under surge-wave voltage. On the other hand in the environment of controlled humidity, the PDIV decreased monotonically as the temperature increased. We found that the PDIV increase was attributed to the effect of the relative humidity decrease corresponding to the temperature increase. Furthermore, the PDIV was also influenced by the water amount in insulation film. The PDIV during the temperature increase was lower than that during the temperature decrease with the hysteresis. The lower PDIV at the higher water amount is due to the release of water into the air gap as well as the decrease in the first ionization energy of insulation film, leading to the increase in the generation probability of an initial electron.</p>

    DOI: 10.1541/ieejfms.139.30

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  21. Simulation on Discharge Inception Voltage Improvement of GIS Spacer with Permittivity Graded Materials (epsilon-FGM) Using Flexible Mixture Casting Method Reviewed International journal

    N. Hayakawa, Y. Miyaji, H. Kojima, K. Kato

    IEEE Transactions on Dielectrics and Electrical Insulation   Vol. 25 ( 4 ) page: 1318 - 1323   2018.8

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    For electric field grading in GIS spacers, the application of functionally graded materials (FGM) with spatial distribution of dielectric permittivity (ε) can be one effective solution. In this paper, we propose the flexible mixture casting (FMC) method as a novel and practical technique to fabricate ε-FGM for GIS spacers. We verified that the relative permittivity (ε r ) can be controlled from ε r = 4 to ε r = 30 by varying the loading ratio of high permittivity filler particles under the FMC method. Toward the practical application of ε-FGM, we verified the relaxation effect of maximum electric field strength and the improvement effect of discharge inception voltage in SF 6 gas in a simplified GIS spacer model using ε-FGM under the FMC method. Simulation results revealed that the maximum electric field strength can be effectively reduced and the discharge inception voltage can be significantly improved compared with using a constant and uniform permittivity.

    DOI: 10.1109/TDEI.2018.007236

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  22. Volume Effect of Dynamic Breakdown Strength in LN2 for Insulation Design of Resistive Superconducting Fault Current Limiters Reviewed International journal

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

    IEEE Transactions on Applied Superconductivity   Vol. 28 ( 4 ) page: 5600804   2018.6

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    Toward the practical and rational insulation design of a resistive superconducting fault current limiter, it is necessary to consider the electrical breakdown (BD) due to the transient bubble generation in liquid nitrogen (LN2) at the quench of the HTS materials. We have been investigating the intrinsic BD characteristics of LN2 without bubbles and the dynamic BD characteristics of LN2 under transient bubble disturbance, respectively. In this paper, we have investigated the dynamic BD characteristics of LN2 for different electrode diameters and gap lengths, and have discussed in terms of the volume effect of dynamic BD strength.

    DOI: 10.1109/TASC.2018.2799308

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  23. Fault Current Limitation Coordination in Electric Power Grid With Superconducting Fault Current Limiters Reviewed International journal

    N. Hayakawa, Y. Maeno, H. Kojima

    IEEE Transactions on Applied Superconductivity   Vol. 28 ( 4 ) page: 5602304   2018.6

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    This paper proposes the concept of “fault current limitation coordination” in a future electric power grid with multiple superconducting fault current limiters (SFCL). Not only the fault current limitation of each SFCL on a transmission line, but also the transient stability of the grid with SFCLs should be taken into account, because the disturbance is brought about in the grid by the sudden appearance and disappearance of a large impedance of SFCL at the fault current limitation and recovery after the fault clearance, respectively. In this paper, both of the fault current limitation of SFCLs and the internal phase angle oscillation of generators were calculated by PSCAD/EMTDC to evaluate the operational feasibility or coordination of SFCLs in a 275/77-kV transmission system model.

    DOI: 10.1109/TASC.2018.2818279

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  24. Fabrication of GIS Spacer Model with ε-FGM (Functionally Graded Materials) and Theoretical Estimation of its Breakdown Voltage in SF6 Gas Reviewed

    Y. Miyaji, H. Kojima, K. Kato, N. Hayakawa

    IEEJ Transactions on Fundamentals and Materials   Vol. 138 ( 4 ) page: 155 - 162   2018.4

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    Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher:The Institute of Electrical Engineers of Japan  

    <p>For the relaxation and optimization of electric field distribution around Gas insulated switchgear (GIS) spacers, the application of functionally graded materials (FGM) with spatial distribution of dielectric permittivity (ε) can be one of the effective solutions. In this paper, we fabricated the coaxial disk-type ε-FGM using SrTiO<sub>3</sub>/SiO<sub>2</sub> particles by the centrifugal force method. We also proposed the coaxial cone-type ε-FGM by the flexible mixture casting method and evaluated its electric field reduction effect and breakdown voltage in SF<sub>6</sub> gas by the volume-time theory.</p>

    DOI: 10.1541/ieejfms.138.155

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  25. Improvement Mechanism of AC Breakdown Voltage of Insulating Oil with Dispersed Nanoparticles Invited International journal

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

    Electronics and Communications in Japan   Vol. 100 ( 12 ) page: 69 - 75   2017.12

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    We investigated the fundamental insulation characteristics of insulating oil with dispersed nanoparticles. The AC breakdown voltage of the insulating oil increased by mixing the dispersed hydrophilic nanoparticles, because the hydrophilic nanoparticles absorbed moisture in the oil, which decreased the number of weak points in the oil for breakdown. In contrast, the hydrophobic nanoparticles did not contribute to the increase of AC breakdown voltage, and decreased the AC breakdown voltage. On the other hand, in the case of overdosing of nanoparticles, the aggregation of nanoparticles caused the decrease in the AC breakdown voltage of the oil, which depended upon the volume concentration of nanoparticles regardless of the diameter of nanoparticles. The aggregation of nanoparticles was led by dielectrophoresis phenomenon, which brought the gap length dependence of the AC breakdown voltage of the insulating oil with the dispersed nanoparticles, because the gradient of electric field strength at the gap was smaller in the case of shorter gap length.

    DOI: 10.1002/ecj.12016

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  26. Discharge Pattern Discrimination in Vacuum Interrupter with Non-contact Measurement of Shield Potential Reviewed International journal

    F. Kong, H. Kojima, N. Hayakawa, T. Kimura, M. Tsukima

    IEEE Transactions on Dielectrics and Electrical Insulation   Vol. 24 ( 5 ) page: 3265 - 3269   2017.10

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    Vacuum interrupter has a composite insulation system. When an internal insulation fails, the discharge has complex and various patterns. Previously, based on the discharge development characteristics, we proposed a discrimination method for the discharge pattern in vacuum interrupter. We measured the applied voltage, anode current, and shield potential waveforms, respectively. From the analysis of the measured waveforms, we can estimate the discharge patterns and discharge path lengths. In this paper, a non-contact shield potential measurement was proposed when the shield potential cannot be measured directly. Furthermore, verification tests with this measurement method were conducted and the effectiveness of the discrimination method was confirmed.

    DOI: 10.1109/TDEI.2017.006512

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  27. Optimum Breakdown Charge for Maximum Dielectric Strength in Spark Conditioning in Vacuum under a Non-uniform Electric Field Reviewed International journal

    H. Kojima, T. Takahashi, N. Hayakawa, K. Hasegawa, M. Sakaki

    IEEE Transactions on Dielectrics and Electrical Insulation   Vol. 24 ( 4 ) page: 2660 - 2665   2017.8

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    Spark conditioning is an effective method of increasing the dielectric strength in vacuum. In this paper, we determined the breakdown (BD) charge dependence for spark conditioning in vacuum under various non-uniform electric fields and with different anode materials. We discuss the BD mechanism in terms of BD arising from anode heating or cathode heating. Experimental results revealed that for anode heating BD, the longer the gap distance, the larger the BD charge needed to obtain maximum dielectric strength. In contrast, for cathode heating BD, the BD charge for maximum dielectric strength was smaller than that for anode heating BD. From these results, we estimated the optimal BD charge to maximize the 50% BD electric field strength, i.e. the dielectric strength, for spark conditioning in vacuum.

    DOI: 10.1109/TDEI.2017.006462

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  28. Discharge Pattern Discrimination for Composite Insulation System in Vacuum Invited International journal

    F. Kong, H. Kojima, T. Kimura, M. Tsukima, N. Hayakawa

    Electrical Engineering in Japan   Vol. 200 ( 3 ) page: 3 - 12   2017.8

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    In order to develop higher-voltage vacuum circuit breakers (VCBs), the investigation of discharge phenomenon in vacuum is necessary. In vacuum interrupters (VIs) with composite insulation systems, the discharge has complex and various patterns at the internal insulation failures. In this paper, based on the discharge development characteristics, we propose a discrimination method for the discharge pattern in vacuum. We measured the applied voltage, anode current, and shield potential waveforms, respectively. From the feature of the measured waveforms, we classified the discharge patterns. Furthermore, based on the relation between discharge development time and discharge path length, we estimated the discharge patterns and discharge path lengths. In addition, we conducted a verification experiment of the discrimination method using a VI model. Experimental results revealed that the estimated discharge patterns and discharge path lengths were consistent with the observed discharge ones and the effectiveness of the discrimination method was confirmed.

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  29. Breakdown Characteristics and Mechanisms of Liquid Nitrogen under Transient Thermal Stress for Superconducting Fault Current Limiters Reviewed International journal

    N. Hayakawa, T. Matsuoka, H. Kojima, S. Isojima, M. Kuwata

    IEEE Transactions on Applied Superconductivity   Vol. 27 ( 4 ) page: 7700305 - 7700305   2017.6

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    We have been investigating the electrical breakdown (BD) characteristics of liquid nitrogen (LN2) with a transient thermal stresses to simulate the quench conditions of resistive-type superconducting fault current limiters (SFCL). We call such BD of LN2 with the transient thermal stress as “dynamic BD,” and discriminate it from that with a continuous thermal stress. In this paper, we investigated the dynamic BD characteristics of LN2 for different LN2 pressures, electrode sizes, and terms of transient thermal stress input. In addition, we obtained the BD characteristics of LN2 with the continuous thermal stress, and compared them with the dynamic BD characteristics. Furthermore, we analyzed the statistical scattering of the time from the thermal stress input to the dynamic BD occurrence and discussed the dynamic BD mechanisms of LN2. We also proposed a flowchart of rational and reliable electrical insulation design of resistive-type SFCL based on the dynamic BD characteristics of LN2.

    DOI: 10.1109/TASC.2017.2651115

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  30. Electrical Insulation Characteristics and Mechanisms of Low Dielectric Loss Materials for High-Voltage HTS Cables Reviewed International journal

    N. Hayakawa, K. Ishida, T. Matsuoka, H. Kojima

    IEEE Transactions on Applied Superconductivity   Vol. 27 ( 4 ) page: 4800904 - 4800904   2017.6

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    Toward the practical development of high-voltage high-temperature superconducting (HTS) cables, high electrical insulation characteristics, and low dielectric loss become important. Dielectric loss drastically increases with the increase of operation voltage of HTS cables. Therefore, it is highly expected to find a novel insulating material with low dielectric loss for the high-voltage HTS cables. We have focused on Tyvek®, polyethylene (PE) nonwoven fabric, and Tyvek®/PE, a syntactic paper bonding PE-sheet on Tyvek® by heat, as low dielectric loss materials. In this paper, we investigated fundamental partial discharge inception characteristics and their mechanisms of Tyvek® immersed in liquid nitrogen (LN2).In addition, we compared the electrical insulation characteristics of Tyvek®, Tyvek®/PE, and polypropylene laminated paper (PPLP®), and discussed their mechanisms.

    DOI: 10.1109/TASC.2016.2645796

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  31. Calculation Model for Predicting Partial-discharge Inception Voltage in a Non-uniform Air Gap while Considering the Effect of Humidity Reviewed International journal

    T. Rokunohe, T. Kato, H. Kojima, N. Hayakawa, H. Okubo

    IEEE Transactions on Dielectrics and Electrical Insulation   Vol. 24 ( 2 ) page: 1123 - 1130   2017.4

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    A calculation model for predicting the inception of partial discharge (PD) in a non-uniform air gap on the basis of theories of electron avalanche and streamer phenomena is proposed. "Partial discharge inception voltages" (PDIVs), under an assumed absolute humidity of less than 20g/cm3, calculated using the proposed model were compared with experimentally measured ones and found to be almost equivalent. Furthermore, the relationship between negative ions and humidity was incorporated into the calculation model, and it was confirmed that the calculated and measured PDIVs tend to be the roughly the same under a wide humidity range under various gap length between electrodes. The proposed partial-discharge inception model based on theories mentioned above was therefore judged to be effective for predicting changes in PDIV when humidity changes.

    DOI: 10.1109/TDEI.2017.005920

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  32. Improvement Mechanism of AC Breakdown Voltage of Insulating Oil with Dispersed Nanoparticles Reviewed

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

    IEEJ Transactions on Fundamentals and Materials   Vol. 137 ( 2 ) page: 101 - 106   2017.2

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    <p>We investigated the fundamental insulation characteristics of insulating oil with dispersed nanoparticles. The AC breakdown voltage of the insulating oil increased by mixing the dispersed hydrophilic nanoparticles, because the hydrophilic nanoparticles absorbed moisture in the oil, which decreased the number of weak points in the oil for breakdown. In contrast, the hydrophobic nanoparticles did not contribute to the increase of AC breakdown voltage, and decreased the AC breakdown voltage. On the other hand, in the case of overdosing of nanoparticles, the aggregation of nanoparticles caused the decrease in the AC breakdown voltage of the oil, which depended upon the volume concentration of nanoparticles regardless of the diameter of nanoparticles. The aggregation of nanoparticles was led by dielectrophoresis phenomenon, which brought the gap length dependence of the AC breakdown voltage of the insulating oil with the dispersed nanoparticles, because the gradient of electric field strength at the gap was smaller in the case of shorter gap length.</p>

    DOI: 10.1541/ieejfms.137.101

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  33. Reduction Method of Fluctuation in Partial Discharge Inception Voltage for Inverter-Fed Rectangular Wire Motors Invited International journal

    T. Wakimoto, H. Kojima, N. Hayakawa

    Electrical Engineering in Japan   Vol. 198 ( 2 ) page: 3 - 10   2017.1

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    We investigated the decisive factors that affect partial discharge inception voltage (PDIV) fluctuation between the coil wires under a sinusoidal voltage by using a rectangular wire motor. As a result, we found that PDIV under low humidity fluctuates by the surface charge, and PDIV under high humidity varies transitionally with the surface conductivity activated by predischarge. From these analyses, we proposed the measurement method of PDIV with a low fluctuation and transition for the rectangular wire motors, which will be optimized by environmental humidity, predischarge condition, and measuring frequency.

    DOI: 10.1002/eej.22908

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  34. Measurement and Evaluation of Partial Discharge Inception Voltage for Enameled Rectangular Wires under AC Voltage Reviewed International journal

    T. Wakimoto, H. Kojima, N. Hayakawa

    IEEE Transactions on Dielectrics and Electrical Insulation   Vol. 23 ( 6 ) page: 3566 - 3574   2016.12

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    Recently, the market for EVs (Electric vehicles) and HEVs (Hybrid electric vehicles) has been expanding. In these vehicles, rectangular wires have started to be used for the traction motor coil to increase the motor performance. As a result, the insulation techniques become important because the applied voltage between the wires is increasing due to a change in the motor structure and the increase in the driving voltage. In order to safeguard the motor insulation, partial discharge (PD) between coil wires must be controlled, and to do this, the coil wires should be coated with an insulator of a suitable thickness. For this purpose, the PD measurement technique is important in design and inspection on the manufacturing lines. However, the PD measurement between wires is unstable, and is especially affected by the measurement method and environmental factors. In this paper, we clarify the factors as well as the mechanism affecting the PD inception voltage (PDIV) between enameled rectangular wires under AC voltage. The effects of the ambient humidity, the pre-discharge conditions and the measuring frequency on the PDIV were analyzed. As a result, it was confirmed that when there was pre-discharge in a high humidity environment, the PDIV displayed fluctuating characteristics in which it momentarily decreased and then increased. We observed the discharges and analyzed the electric field distribution. The results showed that in high humidity environment, pre-discharge causes moisture contained in the air to adhere to the coating surfaces, resulting in an increase in the surface conductivity, which influences the electric field strength in the air gap between coil wires. These analyses indicated that the PDIV can be measured stably and reliably at high frequencies in a high humidity environment.

    DOI: 10.1109/TDEI.2016.005645

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  35. Dependence of Spark Conditioning on Breakdown Charge and Electrode Material under a Non-Uniform Electric Field in Vacuum Reviewed International journal

    H. Kojima, T. Takahashi, N. Hayakawa, K. Hasegawa, H. Saito, M. Sakaki

    IEEE Transactions on Dielectrics and Electrical Insulation   Vol. 23 ( 5 ) page: 3224 - 3230   2016.10

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    Spark conditioning is an effective method for improving dielectric strength in vacuum. In this paper, we discuss the dependence of spark conditioning on breakdown (BD) charge and electrode material in vacuum under various non-uniform electric field and circuit parameters. We applied a negative impulse voltage to a rod-plane electrode configuration with a cathode made of stainless steel (SS), Cu-Cr, or OFHC Cu (Cu), and an anode made of SS or Cu. We changed the gap distance, the tip radius of the rod electrode and the circuit parameters. As a result, the conditioning effect, i.e. improving BD electric field strength by the conditioning, depended on the BD charge (QBD) and reached its maximum value against QBD. The optimal QBD required to achieve the maximum conditioning effect decreased with the cathode melting point. Moreover, when BD caused by cathode heating (CH-BD) occurred readily, with the SS anode, the BD electric field strength at the cathode surface after conditioning depended on QBD, regardless of the gap distance and the tip radius. Thus, for CH-BD, we estimated the withstand voltage that could be achieved by spark conditioning from the electrode configuration and QBD. However, when BD caused by anode heating (AH-BD) occurred easily with the Cu anode, the optimal QBD was larger than that for CH-BD because the cathode temperature was lower for AH-BD than for CH-BD.

    DOI: 10.1109/TDEI.2016.7736889

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  36. Discharge Pattern Discrimination for Composite Insulation System in Vacuum Reviewed

    F. Kong, H. Kojima, T. Kimura, M. Tsukima, N. Hayakawa

    IEEJ Transactions on Fundamentals and Materials   Vol. 136 ( 9 ) page: 594 - 602   2016.9

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    In order to develop higher-voltage vacuum circuit breakers (VCB), the investigation of discharge phenomenon in vacuum is necessary. In vacuum interrupters (VI) with composite insulation systems, the discharge has complex and various patterns at the internal insulation failures. In this paper, based on the discharge development characteristics, we propose a discrimination method for the discharge pattern in vacuum. We measured the applied voltage, anode current, and shield potential waveforms, respectively. From the feature of the measured waveforms, we classified the discharge patterns. Furthermore, based on the relation between discharge development time and discharge path length, we estimated the discharge patterns and discharge path lengths. In addition, we conducted a verification experiment of the discrimination method using a VI model. Experimental results revealed that the estimated discharge patterns and discharge path lengths were consistent with the observed discharge ones and the effectiveness of the discrimination method was confirmed.

    DOI: 10.1541/ieejfms.136.594

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  37. Discharge Characteristics for Various Discharge Patterns under Negative Lightning Impulse Voltage in Vacuum Reviewed International journal

    F. Kong, Y. Nakano, H. Kojima, N. Hayakawa, T. Kimura, M. Tsukima

    IEEE Transactions on Dielectrics and Electrical Insulation   Vol. 23 ( 2 ) page: 813 - 816   2016.4

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    In order to develop higher voltage vacuum interrupters (VIs), electrical insulation performances in vacuum should be improved. The discharge in VI has various and complex patterns, such as breakdown in vacuum gap and surface flashover on a solid insulator. In this paper, we investigated three discharge patterns: the discharge in vacuum gap, the discharge in vacuum gap via shield, and the surface flashover on solid insulator, respectively. By measuring shield potential and insulator surface potential, we analyzed the discharge characteristics for various patterns, and clarified the relevant discharge development process. We found that the breakdown development process in vacuum gap depends on the gap length and the surface flashover development process on a solid insulator depends on the applied voltage and surface distance.

    DOI: 10.1109/TDEI.2015.005388

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  38. Discharge Characteristics of Composite Insulation System with Floating Electrode and Solid Insulator in Vacuum Reviewed International journal

    F. Kong, Y. Nakano, H. Kojima, N. Hayakawa, T. Kimura, M. Tsukima

    IEEE Transactions on Dielectrics and Electrical Insulation   Vol. 23 ( 2 ) page: 1219 - 1225   2016.4

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    For the development of vacuum interrupters for their higher voltage application in power transmission systems, it is necessary to clarify the discharge characteristics of composite insulation systems with a shield (floating electrode) and a solid insulator in vacuum. In this paper, we focus on the composite discharge patterns via the shield and the solid insulator. For cathode-shield-insulator-anode (c-s-i-a) and cathode-insulator-shield-anode (c-i-s-a) electrode configurations, the discharge can be classified into two independent processes: breakdown in vacuum gap and surface flashover on the solid insulator. Furthermore, we have found that the breakdown development time increases with the increase in the gap length and the surface flashover development time depends on the voltage peak after flashover inception, which are consistent with discharge development characteristics for individual gap breakdown and surface flashover, respectively. These results are significant to understanding and discriminating the composite discharge patterns and discharge path in vacuum interrupters.

    DOI: 10.1109/TDEI.2015.005588

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  39. Pressure Dependence and Size Effect of LN2 Breakdown Characteristics Under Transient Thermal Stress Reviewed International journal

    N. Hayakawa, T. Matsuoka, K. Ishida, H. Kojima, S. Isojima, M. Kuwata

    IEEE Transactions on Applied Superconductivity   Vol. 26 ( 3 ) page: 7700604   2016.4

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    Electrical insulation of liquid nitrogen (LN2) for a high-temperature superconducting (HTS) power apparatus can be categorized into two breakdown (BD) modes. One is the intrinsic or conventional BD of LN2. The other is the BD of LN2 with transient bubbles, such as a quench. In this paper, the BD characteristics of LN2 with transient bubbles were investigated for different LN2 pressures and electrode diameters. Experimental results revealed that the BD strength of LN2 with transient bubbles was lower than the intrinsic BD strength of LN2. The difference between the intrinsic BD strength and the BD strength with transient bubbles in LN2 became smaller with the increase in the LN2 pressure and electrode diameter. Furthermore, the BD characteristics of LN2 with continuous bubbles were investigated and compared with the BD characteristics of LN2 with transient bubbles. As a result, the insulation design of an HTS power apparatus in consideration of their quench condition will be rationalized than the design based on the continuous thermal stress.

    DOI: 10.1109/TASC.2016.2532469

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  40. Effective Secondary Electron Emission Coefficient under Transient Surface Charging on Insulator in Surface Flashover Development in Vacuum Reviewed

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

    IEEJ Transactions on Fundamentals and Materials   Vol. 136 ( 3 ) page: 128 - 134   2016.3

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    Based on the mechanism of surface flashover development in vacuum, we have investigated that the surface flashover can be suppressed by the increase in electric field perpendicular to the insulator surface. In this study, we clarified the suppression conditions of surface flashover in terms of the transient surface charge and the effective secondary electron emission coefficient along the insulator surface.

    DOI: 10.1541/ieejfms.136.128

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  41. Reduction Method of Fluctuation in Partial Discharge Inception Voltage for Inverter-fed Rectangular Wire Motors Reviewed

    T. Wakimoto, H. Kojima, N. Hayakawa

    IEEJ Transactions on Fundamentals and Materials   Vol. 136 ( 3 ) page: 121 - 127   2016.3

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    We investigated the decisive factors which affect partial discharge inception voltage (PDIV) fluctuation between the coil wires under a sinusoidal voltage by using a rectangular wire motor. As the result, we found that PDIV under low humidity fluctuates by the surface charge, and PDIV under high humidity varies transitionally with the surface conductivity activated by pre-discharge. From these analyses, we proposed the measurement method of PDIV with a low fluctuation and transition for the rectangular wire motors, which will be optimized by environmental humidity, pre-discharge condition and measuring frequency.

    DOI: 10.1541/ieejfms.136.121

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  42. Fabrication and Simulation of Permittivity Graded Materials for Electric Field Grading of Gas Insulated Power Apparatus Reviewed International journal

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

    IEEE Transactions on Dielectrics and Electrical Insulation   Vol. 23 ( 1 ) page: 547 - 554   2016.2

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    An innovation for the higher performance and reliability of electric power apparatus can be brought about by a novel technique on electrical insulating materials. The application of functionally graded materials (FGM) with spatial distribution of dielectric permittivity in solid insulator is an effective technique to contribute to the above innovation, because FGM can control the electric field distribution with a simple shape. In this paper, we investigated the fabrication and simulation techniques of FGM with various spatial distributions of dielectric permittivity using centrifugal force. Firstly, we developed a simulation technique to estimate the dielectric permittivity distribution of FGM by considering the particle movement in a viscous fluid under centrifugal force. Secondly, based on the simulation technique, we fabricated FGM samples with various relative permittivity distribution and confirmed the validity of the simulation technique. Consequently, the fabrication results provided a good agreement with the simulation results.

    DOI: 10.1109/TDEI.2015.005237

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  43. Classification of Impulse Breakdown Mechanisms under Non-uniform Electric Field in Air Reviewed International journal

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

    IEEE Transactions on Dielectrics and Electrical Insulation   Vol. 23 ( 1 ) page: 194 - 201   2016.2

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    To clarify the breakdown mechanism and the conditions leading to the breakdown under non-uniform electric field in air, we studied the details of breakdown characteristics and mechanism in air by using an ultra-high speed measurement system. We clarified that there were two types of breakdown mechanism in air. The one is the channel heating breakdown, and the other is the leader-Type channel development breakdown. These breakdown mechanisms are dominated by three conditions: Arrival of secondary streamer from high-voltage anode to opposite grounded cathode, channel heating, and leader-Type channel initiation. We studied these conditions quantitatively, and revealed the conditions leading to the breakdown, and the breakdown mechanisms in air were classified. Finally, we clarified the factors, e.g. critical instantaneous power for the secondary streamer arrival, dominating these conditions based on the breakdown mechanism under non-uniform electric field in air.

    DOI: 10.1109/TDEI.2015.005352

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  44. Analysis of Conditioning and Damaging Process in Vacuum based on Breakdown Probability Distribution Reviewed International journal

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

    IEEE Transactions on Dielectrics and Electrical Insulation   Vol. 23 ( 1 ) page: 43 - 48   2016.2

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    For the enhancement of insulation strength in vacuum, spark conditioning is an important and effective method. In order to enhance the insulation performance of vacuum circuit breakers, we have to clarify the conditioning effect and improve a conditioning procedure. In this paper, we discuss the conditioning process of Cu and stainless steel rod electrodes based on breakdown (BD) probability distribution. We applied a negative impulse voltage to a rod-plane electrode configuration. We adopted two procedures for the voltage application, i.e. up-down and 3 times methods. For the Cu rod with the up-down method, BD voltage increased by the conditioning effect, however, the minimum BD voltage did not increase or even decreased due to the damaging effect by BD. A moderate conditioning procedure, e.g. 3 times method, could increase the minimum BD voltage as well as the stabilization of insulation strength. The Weibull analysis of the development of a BD probability distribution has enabled us to discriminate the conditioning and damaging effects. Based on these results, we can discuss a suitable conditioning procedure.

    DOI: 10.1109/TDEI.2015.005248

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  45. Control and Suppression of Impulse Surface Flashover in Vacuum Based on Discharge Development Mechanisms Reviewed International journal

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

    IEEE Transactions on Dielectrics and Electrical Insulation   Vol. 23 ( 1 ) page: 35 - 42   2016.2

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    Surface discharge on solid insulator in vacuum is one of the significant issues for the development of vacuum circuit breakers (VCBs) and vacuum interrupters (VIs). For the development of higher voltage VCBs and VIs, control and suppression techniques of the surface flashover are required. The aim of present study is to suppress the surface flashover, based on physical mechanisms of flashover development. Impulse surface flashover in vacuum, starting with explosive electron emission (EEE) from cathode, develops with the formation of transient charge on the insulator as well as the development of secondary electron emission avalanche (SEEA) along the surface toward anode. To reduce the EEE current from the cathode and the SEEA development, we changed the electrode geometry such as thickness of alumina ceramics and tip radius of cathode rod, respectively, and installed a plane electrode as the back electrode of the cathode rod. As the results, EEE current was reduced by the field relaxation effect of transient charging due to EEE, and SEEA was also suppressed by the perpendicular electric field of the plane electrode. When the flashover was suppressed by using the cathode back electrode, transient charge amount was smaller on alumina dielectrics at the end of the plane electrode area. From the above results, it would be an effective technique for the control and suppression of surface flashover in vacuum to enlarge the perpendicular electric field for the insulator.

    DOI: 10.1109/TDEI.2015.005307

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  46. Transient Charging Characteristics in Surface Flashover Development Process due to Explosive Electron Emission in Vacuum Invited International journal

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

    Electrical Engineering in Japan   Vol. 193 ( 2 ) page: 10 - 17   2015.11

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    For the development of higher voltage vacuum circuit breakers and vacuum interrupters, surface discharge in a vacuum is one of the most significant issues. We measured the charge activity on alumina dielectrics in a vacuum through ultrahigh-speed optical and electrical measurements. We found that surface flashover in a vacuum starts with an explosive electron emission (EEE) with higher current density, which consists of electron emission from the cathode, and results in surface flashover development. The transient charge on the alumina dielectrics formed by electrons emitted by EEE influences the distortion of electric field distribution around the cathode rod and then the subsequent flashover development. In particular, in the case of a shorter gap between the cathode rod and the alumina dielectrics, the electron emission may be suppressed by the relaxation effect of the electric field due to transient charge accumulation.

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  47. Size Effect on Breakdown Strength in Sub-cooled Liquid Nitrogen for Superconducting Power Apparatus Reviewed International journal

    N. Hayakawa, S. Nishimachi, H. Kojima, H. Okubo

    IEEE Transactions on Dielectrics and Electrical Insulation   Vol. 22 ( 5 ) page: 2565 - 2571   2015.10

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    Toward the practical and rational insulation design of high temperature superconducting power apparatus, the ac breakdown (BD) characteristics and mechanisms of liquid nitrogen (LN2) were systematically investigated and discussed for different pressures at P = 0.1-0.3 MPa and temperatures at T = 65-77 K under quasiuniform electric field with the field utilization factor ζ= 0.986-0.674. We obtained the BD strength (EB) in sub-cooled LN2 (SLN2) and analyzed them in terms of size effect, taking account of the stressed liquid volume (SLV) with the electric field distribution in SLN2. Together with the other researchers' data on BD characteristics of LN2, we extended the evaluation by applying the concept of α% SLV (SLV with the electric field strength higher than the decisive electric field factor, α of the maximum electric field strength). As the result, we derived that EB with the 50 % probability decreased linearly with the increase in α% SLV on a universal line, EB = 78.4 × (α% SLV)-1/8.15, which was irrespective of the pressure and temperature of LN2.

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  48. Impulse Surface Flashover Development Associated with Transient Charging by Explosive Electron Emission in Vacuum Reviewed International journal

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

    IEEE Transactions on Dielectrics and Electrical Insulation   Vol. 22 ( 4 ) page: 2390 - 2397   2015.8

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    Surface discharge on solid insulator in vacuum, which is one of the most significant issues under high electric field, prevents the development of higher voltage vacuum circuit breakers and vacuum interrupters. To clarify the mechanism of the surface discharge in vacuum, charge activities on solid insulators in the development process of the surface discharge should be investigated. By using electrostatic probes behind the alumina dielectrics and measuring fast-framing images of the surface discharge, in the present paper, we clarified that the impulse surface flashover starts in developing with explosive electron emission (EEE) on cathode, which is specific phenomenon on the electron emission site exploding due to extreme field emission current density. Experimental results revealed the characteristics of transient charging by EEE in the surface flash over development as follows: (1) the probe current due to EEE increases with the EEE inception electric field on the cathode, and also depends on the work function of the cathode material, (2) the transient charge distribution on the alumina dielectrics is determined by the EEE spot on the cathode, (3) EEE occurs several times due to the erosion and the regeneration of electron emission sites. (4) the successive EEE makes the transient charge distribution smooth on the alumina dielectrics.

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  49. Fault Current Limitation Coordination in Power Transmission System With Superconducting Fault Current Limiting Cables (SFCLC) Reviewed International journal

    H. Kojima, T. Osawa, N. Hayakawa

    IEEE Transactions on Applied Superconductivity   Vol. 25 ( 3 ) page: 5401904   2015.6

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    We investigate a Superconducting Fault Current Limiting Cable (SFCLC), which is an HTS cable with fault current limiting function. From the viewpoint of the fault current limitation coordination in a power transmission system, it is necessary to investigate the interaction of current limiting functions between multiple SFCLCs introduced in the system. We constructed a numerical model to analyze electrical and thermal behaviors of SFCLC based on resistance generation characteristics of superconductors. In the model power system, two SFCLCs were connected in parallel and two fault points were assumed. We calculated the current limiting characteristics of each SFCLC in the model system, and evaluated the current limitation effect and temperature rise of SFCLCs on each fault point. Depending on the fault point, there are two types of substantial connection of SFCLCs, namely in series and in parallel during the fault. In the substantially parallel connection, each SFCLC operates as the case of single SFCLC introduction. In the substantially series connection, the current limiting effect is determined by SFCLC with the smaller critical current. These results imply that the efficiency and reliability of a power transmission system will be improved by the introduction of multiple SFCLCs, as well as the single SFCLC.

    DOI: 10.1109/TASC.2015.2392251

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  50. Quench-Induced Dynamic Breakdown Characteristics of LN2 and LN2/PPLP Composite Electrical Insulation System for Superconducting Power Apparatus Reviewed International journal

    N. Hayakawa, T. Matsuoka, S. Nishimachi, H. Kojima

    IEEE Transactions on Applied Superconductivity   Vol. 25 ( 3 ) page: 7700304   2015.6

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    In HTS power apparatus, quench due to the fault current generates dynamic electrical/thermal combined stress. This stress may induce the electric breakdown (BD) under the operating voltage. We investigated the quench-induced dynamic BD characteristics of LN2. In addition we investigated the quench-induced dynamic partial discharge characteristics of LN2/polypropylene laminated paper composite electrical insulation system for HTS cables. The criteria of the combined electrical/thermal stress for the dynamic BD were obtained for both test samples, and the reduction rate of the dynamic BD criteria against the static BD criteria without thermal stress was discussed.

    DOI: 10.1109/TASC.2014.2361405

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  51. Power Flow Control and Maintenance Strategy of Transformers in Transmission and Distribution Systems Reviewed

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

    IEEJ Transactions on Power and Energy   Vol. 135 ( 5 ) page: 316 - 321   2015.5

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    Transmission and distribution (T&D) systems for electric power are assembled with a large amount of aged apparatus, the deterioration of which may cause a decrease in reliability. In order to maintain high efficiency and high quality in T&D systems, it is important to minimize both present performance costs and future performance costs. Typical present performance costs are T&D losses, and typical future performance costs are failure losses and apparatus maintenance for overall T&D system optimization. We have to consider concurrently two concepts that are an asset management system and a smart grid. This integrated concept, which we have proposed as Intelligent Grid Management System (IGMS), achieves optimum control that includes the present power flow and the future maintenance of the T&D system. In this paper, the effect of temperature rises in transformer windings is formulated and integrated into an objective function to determine transformers with power flow control. The derived power flow control optimizes the load sharing of each transformer by keeping a balance between the T&D loss and degradation in the transformers. The degradation of aged transformers is prevented by reducing their load factor, or the aged transformer is replaced with a new one that accepts a relatively high load factor.

    DOI: 10.1541/ieejpes.135.316

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  52. Transient Charging Characteristics in Surface Flashover Development Process due to Explosive Electron Emission in Vacuum Reviewed

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

    IEEJ Transactions on Fundamentals and Materials   Vol. 134 ( 11 ) page: 578 - 584   2014.11

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    For the development of higher voltage vacuum circuit breakers (VCB) and vacuum interrupters (VI), surface discharge phenomenon in vacuum is one of the most significant issues. We measured the charge activity on alumina dielectrics in vacuum through ultra-high speed optical and electrical measurements. We found out that the surface flashover in vacuum starts with an explosive electron emission (EEE) with the higher current density, which is the electron emission from the cathode, and results in the surface flashover development. Transient charge on the alumina dielectrics formed by electrons emitted by EEE influences the distortion of electric field distribution around the cathode rod and then the subsequent flashover development. Especially, in the case of the shorter gap between the cathode rod and the alumina dielectrics, the electron emission could be suppressed by the relaxation effect of the electric field due to the transient charge accumulation.

    DOI: 10.1541/ieejfms.134.578

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  53. Influence of Longitudinal Temperature Distribution on Current Limiting Function of Superconducting Fault Current Limiting Cable (SFCLC) Reviewed International journal

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

    Journal of Physics: Conference Series   Vol. 507 ( PART 3 ) page: 032026   2014.5

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    We have proposed a Superconducting Fault Current Limiting Cable (SFCLC), which is an HTS cable with fault current limiting function. SFCLC is expected to limit the fault current and also immediately recover the cable function after the fault clearance. In the SFCLC operation, a longitudinal temperature distribution will exist due to heat penetration, AC loss, dielectric loss and the performance of cryocooling system, which will influence its current limitation characteristics. In this paper, we investigate the influence of the longitudinal temperature distribution on current limiting function and temperature rise after the current limitation of SFCLC. We suggested the effective measures of parameter control, i.e. decreasing the critical current (Ic@77K), n value at flux flow region (n1-0), increasing the coefficient of longitudinal temperature gradient (α), inflow temperature (Tin) to achieve both the higher current limiting function and the lower temperature rise. © Published under licence by IOP Publishing Ltd.

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  54. Technique for Discriminating the Type of PD in SF6 Gas Using the UHF Method and the PD Current with a Metallic Particle Reviewed International journal

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

    IEEE Transactions on Dielectrics and Electrical Insulation   Vol. 21 ( 1 ) page: 88 - 95   2014.2

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    The relationship between the PD current pulse waveform at the PD source and the radiated electromagnetic (EM) waveform is investigated using a needle electrode for a metallic particle in SF6 gas at 0.2MPa. A leader discharge with a larger PD charge magnitude and a longer propagation length than for a streamer discharge can be an indicator of breakdown in the SF6 gas. Simultaneous and synchronous measurement of the PD current, EM signals and light emission in the SF6 gas revealed that it is possible to discriminate between a streamer discharge and a leader discharge in both time and frequency components. Compared with a streamer discharge, a leader discharge is characterized by a longer rise/fall time of around 0.9 ns in the PD current pulse waveform, and by a lower frequency component of around 250 MHz in the EM frequency spectrum. A satisfactory correlation was obtained between the actual measured EM wave spectrum and the spectrum derived using a spectrum analyzer from the product of the actual PD current and the transfer function from the needle electrode to the UHF sensor that receives the EM wave. This new technique enables streamer and leader types of PD in SF6 gas to be discriminated between by measuring the EM wave with a UHF detection system. © 1994-2012 IEEE.

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  55. Pre-discharge and Flashover Characteristics of Impulse Surface Discharge in Vacuum Reviewed International journal

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

    IEEE Transactions on Dielectrics and Electrical Insulation   Vol. 21 ( 1 ) page: 403 - 410   2014.2

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    Surface discharge on solid insulators is one of the significant issues in the development of vacuum circuit breakers (VCB) and vacuum interrupters (VI). We measured the charge activity on alumina dielectrics in vacuum through ultra-high speed and high sensitivity optical measurements. We identified the existence of charge activity with a small light emission on alumina dielectrics before the surface flashover development process, and defined this as a 'pre-discharge' and measured its characteristics. We classified the charge activities into three processes: (1) pre-discharge, (2) surface flashover initiation, and (3) surface flashover expansion, in the development of surface discharge in vacuum. Utilizing this classification, we found that the surface predischarge in vacuum is generated by the electron emission from the cathode, and the subsequent flashover initiates with a steep increase in current and develops with the distortion of the electric field due to transiently-formed charging on the alumina dielectrics in vacuum. © 2013 IEEE.

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  56. Development of a Partial Discharge Inception Calculation Model of a Nonuniform Air Gap Considering the Effect of Humidity Invited International journal

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

    Electrical Engineering in Japan   Vol. 186 ( 3 ) page: 1 - 9   2014.2

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    Insulation design employing discharge simulation based on physics phenomena is used in designing electrical instruments to facilitate their miniaturization and obtain high insulation reliability. We developed a partial discharge inception calculation model for a nonuniform air gap based on the theories of electron avalanche and streamer phenomena. The calculated and experimental PDIVs (Partial Discharge Inception Voltages) were compared under conditions of constant humidity, and we confirmed that these agreed well with each other to within about 10%. Furthermore, we incorporated a relationship between negative ions and humidity into the model and confirmed that the calculated and experimental PDIVs agreed to within about 15%. Therefore, this model was judged to be an effective method for predicting changes in the PDIV when the humidity changes. © 2013 Wiley Periodicals, Inc.

    DOI: 10.1002/eej.22351

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  57. Integration of Asset Management and Smart Grid with Intelligent Grid Management System Reviewed International journal

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

    IEEE Transactions on Dielectrics and Electrical Insulation   Vol. 20 ( 6 ) page: 2195 - 2202   2013.12

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    Electric power transmission and distribution (T and D) systems are composed of a great deal of aged apparatus, which may cause a decrease in reliability owing to their deterioration. In order to maintain high efficiency and high quality in T and D systems, the authors have proposed an "intelligent grid management system" (IGMS), which determines the optimum maintenance strategy and optimum power flow control based on condition monitoring and diagnostic results of the operating power apparatus. This means that the IGMS essentially includes both concepts of an asset management system and a smart grid. Further, the IGMS optimizes power flow routes and maintenance plans based on the failure risk, T and D loss, overload operation, life estimation of the power apparatus, customer outage, and other metrics. The impact of individual apparatus failure affects the entire T and D system's performance, causing blackouts and secondary failures. Reduction in reliability of whole system is highly dependent on ageing of the materials. The IGMS evaluates all of the events occurring in the T & D system as the cost. Additionally, the risks are evaluated in the cost according to the impact of the failure rate estimated by the condition monitoring diagnosis results of the power apparatus. Insulation system determines the transition in reliability and maintenance cost of the system. In this paper, the IGMS is applied to T and D system models including aged apparatus, such as transformers and circuit breakers, and suitable power flow routes and maintenance strategies are derived. Consequently, by the effective application of the IGMS, the system reliability can achieve an optimum state, and the total cost can be minimized. © 2013 IEEE.

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  58. Feasibility Study on Superconducting Power Flow Controller and Fault Current Limiter (SPFCL) Reviewed International journal

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

    IEEE Transactions on Applied Superconductivity   Vol. 23 ( 3 ) page: 5600504   2013.6

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    A superconducting power flow controller and fault current limiter is proposed in this paper, which can not only control power flow in the steady operating state, but also limit fault current in the fault condition. We verified that the superconducting power flow controller and fault current limiter will contribute to the enhancement and coordination of both static stability in the steady operating condition and transient stability in the fault condition. © 2002-2011 IEEE.

    DOI: 10.1109/TASC.2012.2230677

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  59. Physical Mechanisms of Partial Discharges at Nitrogen Filled Delamination in Epoxy Cast Resin Power Apparatus Reviewed International coauthorship International journal

    D.-E. A. Mansour, H. Kojima, N. Hayakawa, M. Hanai, H. Okubo

    IEEE Transactions on Dielectrics and Electrical Insulation   Vol. 20 ( 2 ) page: 454 - 461   2013.4

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    For proper insulation design of epoxy cast resin power apparatus such as molded transformers, it is important to consider the criticality of defects that might exist into the dielectric material. One of the most important defects is the delamination defect at the interface between resin and conductor. Accordingly, this paper aims to investigate partial discharge (PD) characteristics and to clarify their mechanisms for micro gap delamination defect of epoxy cast resin power apparatus. An experimental model simulating delamination defect was built. Nitrogen gas at atmospheric pressure was used as a typical filled gas inside the delamination of epoxy cast resin power apparatus. Simultaneous measurements of PD light emission intensity, PD light emission image and PD current pulse were carried out. PD inception voltage was measured for different delamination depths. PD generation characteristics were recorded. It was found that multiple PD events were detected only by PD light emission images and could not be detected by their current pulses as a result of very small magnitudes of PD current pulses. Time transition of PD activity for 10 minutes were obtained and analyzed using the captured light emission images. Based on the obtained results and comparing with SF6 gas filled delamination, physical mechanisms behind PD activity could be discussed.

    DOI: 10.1109/TDEI.2013.6508747

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  60. Identification of Metallic Particle Defect in GIS Based on Partial Discharge Mechanism Reviewed

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

    IEEJ Transactions on Power and Energy   Vol. 133 ( 1 ) page: 114 - 120   2013.1

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    A metallic particle defect seriously degrades an insulation performance of gas insulated switchgear (GIS). Therefore, the estimation of risk of the metallic particle is important to maintain the reliability of GIS. In this paper, based on a partial discharge (PD) mechanism, we suggest a novel method to estimate the metallic particle defect using PD properties, which are the minimum instantaneous voltage of positive PD extinction, the instantaneous voltage of negative PD inception, and the negative PD pulse number from PD generation characteristics of applied voltage phase.

    DOI: 10.1541/ieejpes.133.114

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  61. Current Limitation and Recovery Function for Superconducting Fault Current Limiting Transformer (SFCLT) Reviewed International journal

    J. Himbele, H. Kojima, N. Hayakawa, M. Hanai, H. Okubo

    Physics Procedia   Vol. 36   page: 841 - 844   2012.9

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    Superconducting Fault Current Limiting Transformer (SFCLT) is expected to have both superconducting transformer function and superconducting fault current limiter function. We have so far developed the 2 MVA-class SFCLT based on YBCO coated conductors, and experimentally evaluated its current limitation and recovery characteristics. In this paper, we constructed a simulation model for current limitation and recovery characteristics of SFCLT for different HTS coil characteristics and design, and derived the optimized design for the effective current limitation and extended recovery criteria under the rated voltage of the 2 MVA-class SFCLT.

    DOI: 10.1016/j.phpro.2012.06.137

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  62. Recent Progress in Electrical Insulation Techniques for HTS Power Apparatus Reviewed International journal

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

    Physics Procedia   Vol. 36   page: 1305 - 1308   2012.9

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    This paper describes the electrical insulation techniques at cryogenic temperatures, i.e. Cryodielectrics, for HTS power apparatus, e.g. HTS power transmission cables, transformers, fault current limiters and SMES. Breakdown and partial discharge characteristics are discussed for different electrical insulation configurations of LN2, sub-cooled LN2, solid, vacuum and their composite insulation systems. Dynamic and static insulation performances with and without taking account of quench in HTS materials are also introduced.

    DOI: 10.1016/j.phpro.2012.06.295

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  63. Superconducting Fault Current Limiting Cable (SFCLC) with Current Limitation and Recovery Function Reviewed International journal

    H. Kojima, F. Kato, N. Hayakawa, M. Hanai, H. Okubo

    Physics Procedia   Vol. 36   page: 1296 - 1300   2012.9

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    We have proposed a Superconducting Fault Current Limiting Cable (SFCLC), which is an HTS cable with fault current limitation function. SFCLC will transmit the bulk power with low loss in steady state, and also limit the fault current during the fault condition, and recover into the superconducting state after the fault clearance. Using a numerical model, we investigated the current limitation and recovery characteristics of SFCLC for different voltage and current levels, and cable lengths. We verified the feasible conditions and performance of SFCLC with the current limitation and recovery function.

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  64. Feasibility Study on a High-Temperature Superconducting Fault-Current-Limiting Cable (SFCLC) Using Flux-Flow Resistance Reviewed International journal

    H. Kojima, F. Kato, N. Hayakawa, M. Hanai, H. Okubo

    IEEE Transactions on Applied Superconductivity   Vol. 22 ( 2 ) page: 4800105 - 4800105   2012.4

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    We propose a high-temperature superconducting fault-current-limiting cable (SFCLC), which is a high-temperature superconducting cable with a fault-current-limiting function. The SFCLC is expected to achieve fault-current limitation by flux-flow resistance of a long cable length. Particularly, in this paper, we focus on E-I-T characteristics of a YBCO-coated conductor at the flux-flow region. Based on the obtained E-I-T characteristics, we develop a numerical model and investigate current-limiting characteristics of the SFCLC for different cable lengths and fault conditions into a model power system.

    DOI: 10.1109/TASC.2011.2173339

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  65. Development of the Partial Discharge Inception Calculation Model in a Non-uniform Air Gap Considering the Effect of Humidity Reviewed

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

    IEEJ Transactions on Fundamentals and Materials   Vol. 131 ( 12 ) page: 1017 - 1023   2011.12

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    Insulation design with discharge simulation based on physics phenomena is used in designing electrical instruments to facilitate their miniaturization and get high insulation reliability. We developed a partial discharge inception calculation model in a non-uniform air gap based on theories of electron avalanche and streamer phenomena. The calculated and experimental PDIVs were compared under a constant humidity condition, and we confirmed these agreed well with each other within about 10 %. Furthermore, we built a relationship between negative ions and humidity into the model, and confirmed the calculated and experimental PDIVs (Partial Discharge Inception Voltage) agreed within about 15 %. Therefore, this model was judged as a method for predicting changes in PDIV when the humidity changes.

    DOI: 10.1541/ieejfms.131.1017

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  66. Conditioning Mechanism of Cu-Cr Electrode Based on Electrode Surface State under Impulse Voltage Application in Vacuum Reviewed International journal

    H. Kojima, N. Hayakawa, R. Nishimura, H. Okubo, H. Sato, H. Saito, Y. Noda

    IEEE Transactions on Dielectrics and Electrical Insulation   Vol. 18 ( 6 ) page: 2108 - 2114   2011.12

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    Because of high insulation performance and environmental-friendliness, vacuum is attracting considerable attention, and vacuum circuit breakers (VCBs) are expected to develop into higher voltage level. In this paper, we investigated the relationship between the surface condition and the conditioning mechanism of Cu-Cr electrode during impulse voltage application in vacuum. The experimental results showed that a layer of anode material was deposited on the cathode surface, owing to the impulse voltage applications. In addition, we investigated the content ratio of cathode and anode material on the surface after the saturation of electrode conditioning and relationship between the breakdown (BD) discharge area and deposited area during electrode conditioning process. We found that under impulse voltage application, the cathode surface characteristics approach the anode material characteristics, but that the content ratio of Cu to Cr differed between the electrodes. This means that anode material could determine the final state of the conditioning process.

    DOI: 10.1109/TDEI.2011.6118651

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  67. Identification of Insulation Defect by Sequential Measurement of Partial Discharge in GIS Reviewed

    M. Yoshida, K. Suzuki, H. Kojima, N. Hayakawa, M. Hanai, H. Okubo

    IEEJ Transactions on Power and Energy   Vol. 131 ( 11 ) page: 905 - 911   2011.11

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    To maintain the insulation reliability on gas insulated switchgear (GIS), several partial discharge (PD) monitoring techniques have been utilized. To estimate the risk of a defect, it is important to identify the kind of defects and its condition. In this paper, every PD pulse of various defect types was sequentially measured by using high-speed PD measuring system. The sequential PD measurement was proved to be useful to identify the defect condition, because the temporal change of PD characteristics could show the accumulation of the space charge around the defect in GIS.

    DOI: 10.1541/ieejpes.131.905

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  68. Analysis of Current Limiting and Recovery Characteristics of Superconducting Fault Current Limiting Transformer (SFCLT) with YBCO Coated Conductors Reviewed International journal

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

    IEEE Transactions on Applied Superconductivity   Vol. 21 ( 3 ) page: 1422 - 1425   2011.6

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    Superconducting Fault Current Limiting Transformer (SFCLT) is expected to function as superconducting transformer in steady state and superconducting fault current limiter in fault condition. We have designed, fabricated and tested SFCLT with YBCO coated conductors to be operated in liquid nitrogen (LN2) at 77 K and verified its technological feasibility. In this paper, we developed a simulation model to analyze electrical and thermal behaviors of SFCLT by solving the circuit equation and the heat conduction equation. By the use of this simulation model, we could evaluate the transition of resistance and temperature of the YBCO coated conductors during the fault current limitation as well as after the fault clearance, and verified the recovery criteria of SFCLT. © 2011 IEEE.

    DOI: 10.1109/TASC.2011.2105234

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  69. Current Limiting and Recovery Characteristics of 2 MVA Class Superconducting Fault Current Limiting Transformer (SFCLT) Reviewed International journal

    H. Kojima, M. Kotari, T. Kito, N. Hayakawa, M. Hanai, H. Okubo

    IEEE Transactions on Applied Superconductivity   Vol. 21 ( 3 ) page: 1401 - 1404   2011.6

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    We have been developing Superconducting Fault Current Limiting Transformer (SFCLT) with the function of both superconducting transformer in steady state and superconducting fault current limiter in fault condition. As the Step-5 of SFCLT project, 2 MVA class HTS-SFCLT using YBCO coated conductors with the ratings of 22 kV/6.6 kV has been developed. One of the important concerns for the development of HTS-SFCLT is the current limiting and recovery characteristics as well as the transformer function. Thus, in this paper, current limitation and recovery tests of the HTS-SFCLT are carried out. The current limiting test have revealed that the HTS-SFCLT exhibits the excellent current limiting function as a superconducting fault current limiter, where the prospective short-circuit current IPRO=784 Apeak is reduced to 34% at the first peak and 18% at the 5th cycles. The HTS-SFCLT has been able to recover into superconducting state immediately after the fault clearance. According to the transition of generated resistance of the HTS-SFCLT, the criteria of recovery into superconducting state are quantified for different combinations of load current before the fault and prospective short-circuit current during the fault.

    DOI: 10.1109/TASC.2010.2089413

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  70. Progress in Development of Superconducting Fault Current Limiting Transformer (SFCLT) Reviewed International journal

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

    IEEE Transactions on Applied Superconductivity   Vol. 21 ( 3 ) page: 1397 - 1400   2011.6

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    We have been developing Superconducting Fault Current Limiting Transformer (SFCLT), which has multifunction of both a superconducting transformer in a steady state as well as a superconducting fault current limiter in a fault condition. This paper introduces the progress in our SFCLT project since 1998, from Step-1 to the latest Step-5, with the concept, design, fabrication and test results of SFCLT. In the latest Step-5, we developed a 2 MVA, 22/6.6 kV class SFCLT with YBCO coated conductors and verified the fundamental function as a transformer, effective current limiting function as a fault current limiter, and recovery characteristics after the fault clearance with its operational criterion.

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  71. Development Process of Impulse Surface Flashover on Alumina Dielectrics in Vacuum Reviewed International journal

    H. Kojima, N. Hayakawa, T. Ishida, H. Okubo, K. Tsuchiya

    IEEE Transactions on Dielectrics and Electrical Insulation   Vol. 18 ( 3 ) page: 918 - 923   2011.6

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    For higher electrical insulation performance of vacuum circuit breakers (VCB), the surface insulation characteristics in vacuum should be improved. In this paper, we investigated the development mechanism of impulse surface flashover on alumina ceramic insulator in vacuum. We measured the still images and ultra fast framing images of fast developing surface flashover in synchronous with applied impulse voltage and current waveforms. The light emission transition in initiation of surface flashover was also clarified. We found the dark area was formed around the cathode and conducting channel was formed from the anode in developing process of surface flashover in vacuum.

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  72. Evaluation of UHF Method for Partial Discharge Measurement by Simultaneous Observation of UHF Signal and Current Pulse Waveforms Reviewed International journal

    M. Yoshida, H. Kojima, N. Hayakawa, F. Endo, H. Okubo

    IEEE Transactions on Dielectrics and Electrical Insulation   Vol. 18 ( 2 ) page: 425 - 431   2011.4

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    The partial discharge - current pulse waveform analyzing (PD-CPWA) system can measure partial discharge (PD) current pulses continuously in high speed, and is being used for the study of PD mechanisms in SF6 gas in a laboratory. On the other hand, the ultra high frequency (UHF) method is becoming popular for the on-site monitoring of gas-insulated switchgears (GIS). The former can detect PD with high accuracy and make it possible to analyze and understand discharge physics in detail. The latter is suitable to detect PD in actual power equipment, even in noisy site condition. Clarification of coincidence of PD characteristics measured with both methods is very important for further application of the UHF method. In this paper, PD current pulses generated from artificial defects in SF6 gas were synchronously measured with both methods. Measured data were analyzed and compared in many PD characteristics. As a result, many characteristics coincided well between them. However, the scatter of PD and the limited equipment performance of the UHF method may cause some detection failures. An appropriate and advanced use of the UHF method was pointed out. © 2011 IEEE.

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  73. Mechanism of Small Current Generation under Impulse Voltage Applications in Vacuum Reviewed

    K. Aoki, H. Yasukawa, H. Kojima, M. Homma, T. Shioiri, H. Okubo

    IEEJ Transactions on Fundamentals and Materials   Vol. 130 ( 9 ) page: 781 - 786   2010.9

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    Small discharge not to accompany breakdown can occur under high electric field in vacuum, however the mechanism is not well clarified. We have found that the current of small discharge decreases with repeated voltage applications, and leads to electrode conditioning effect of raising withstand voltage. The inception of the current is delayed with the decrease of current, and the inception time and waveform change by gap length. On the other hand, under low vacuum condition, the current increases and reaches saturation with repeated voltage applications. From these discussions, we concluded that the generating process of small current depended on the adsorption and absorption gas of electrodes.

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  74. Partial Discharge Activities under AC/Impulse Superimposed Voltage in LN2/Polypropylene Laminated Paper Insulation System for HTS Cables Reviewed International journal

    N. Hayakawa, R. Yamaguchi, Y. Ukai, H. Kojima, F. Endo, H. Okubo

    Journal of Physics: Conference Series   Vol. 234 ( PART 3 ) page: 032020   2010.7

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    This paper discusses electrical insulation characteristics of high temperature superconducting (HTS) cables for their reliable and rational insulation design. We focused on a severe and practical operational condition of HTS cables, i.e. under commercial ac / lightning impulse superimposed voltage. Experimental results for a HTS cable insulation model composed of liquid nitrogen (LN2) and polypropylene (PP) laminated paper revealed that ac / impulse superimposed voltage could trigger partial discharge (PD) by the impulse voltage invasion and cause consecutive PD under the subsequent ac voltage. The PD generation characteristics were summarized for different ac / impulse superimposed voltages, and a criterion for consecutive PD generation was identified. © 2010 IOP Publishing Ltd.

    DOI: 10.1088/1742-6596/234/3/032020

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  75. Development of 2MVA Class Superconducting Fault Current Limiting Transformer (SFCLT) with YBCO Coated Conductors Reviewed International journal

    M. Kotari, H. Kojima, N. Hayakawa, F. Endo, H. Okubo

    Journal of Physics: Conference Series   Vol. 234   page: 032070   2010.7

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  76. Partial Discharges and Associated Mechanisms for Micro Gap Delamination at Epoxy Spacer in GIS Reviewed International journal

    D.A. Mansour, H. Kojima, N. Hayakawa, F. Endo, H. Okubo

    IEEE Transactions on Dielectrics and Electrical Insulation   Vol. 17 ( 3 ) page: 855 - 861   2010.6

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    For accurate detection and diagnosis of Partial Discharges (PDs) in Gas Insulated Switchgears (GISs), there is a need for better understanding of the physical mechanisms for the PD activity. Accordingly, we have been investigating the PD characteristics and associated mechanisms for electrode/epoxy delamination of GIS spacers as one of the severest defects in GIS. The gas pressure inside delamination usually changes from subatmospheric pressure, just after delamination initiates, to filled SF6 gas pressure in the GIS tank, after SF6 gas infiltrates into the delamination area. Therefore, in this paper, the PD activity at different gas pressures, from 0.02 to 0.4 MPa, is acquired. Delamination gap length at the level of 50 μm is considered, simulating possible size of actual delamination in a GIS spacer. The relative PD generation rate is analyzed regarding the phase characteristics at different pressures and then discussed from the viewpoint of PD mechanism in order to assess the possibility of delamination diagnosis in GIS spacers. Experimental results show that, PD parameters and phase characteristics change significantly with infiltrating SF6 gas from the GIS tank into the delamination. The obtained results give a characterized feature for the delamination defect and can be useful for delamination diagnosis.

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  77. Charge Accumulation Effects on Time Transition of Partial Discharge Activity at GIS Spacer Defects Reviewed International journal

    D.-E.A. Mansour, K. Nishizawa, H. Kojima, N. Hayakawa, F. Endo, H. Okubo

    IEEE Transactions on Dielectrics and Electrical Insulation   Vol. 17 ( 1 ) page: 247 - 255   2010.2

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    The partial discharge (PD) measurements are considered as the most important tool for condition monitoring of Gas Insulated Switchgears (GISs). However, if spacer surface is involved in PD activity, charge accumulation process greatly affects the time transition of PD characteristics. This paper investigates this effect considering the defect types of delamination at the electrode/spacer interface and metallic particles adhered to the spacer surface as the most serious defects that can lead to major failure. Two different electrode configurations were built to simulate the two defect types. The PD characteristics were measured and analyzed from immediately after voltage application up to several minutes where steady state characteristics have been obtained. As a result, it was found that the generation rate of PD pulses changed considerably with time for both defect types. This tendency of PD characteristics has been discussed considering the effect of charge accumulation. Comparing these effects for negative and positive PD enabled to clarify the similarities and differences in the charge accumulation effect for both defect types which can contribute to the defect type identification in GIS. It was found that the effects of charge accumulation on the electric field strength for the delamination defect case as well as on the ionization volume for the metallic particle case were the responsible parameters for the different PD tendencies.

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  78. Surface Charge Accumulation and Partial Discharge Activity for Small Gaps of Electrode/Epoxy Interface in SF6 gas Reviewed International journal

    D. Mansour, H. Kojima, N. Hayakawa, F. Endo, H. Okubo

    IEEE Transactions on Dielectrics and Electrical Insulation   Vol. 16 ( 4 ) page: 1150 - 1157   2009.8

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    The electrical insulation reliability of solid spacers in gas insulated switchgears (GISs) is an important issue to achieve a safe operation of such equipment. Among different phenomena, charge accumulation represents the most important matter that can degrade the overall performance of these insulation systems. For this respect, this paper discusses the contribution of partial discharge (PD) activity by ac voltage application to charge accumulation in the small gap at the electrode/epoxy interface as one of the weakest points in GIS solid spacers. The partial discharge inception voltages for non-accumulated charge case (PDIV0) and after exposing to PD activity (PDIVn) are measured among different gap lengths, simulating delamination at the electrode/epoxy interface. The PD activity is generated using applied voltage with 1.2à PDIV0 for all gap lengths examined in this study (50~500 ¿m). In these measurements, PDIV increased with increasing the number of PD pulses as a result of accumulated charges. The accumulated surface charge density is estimated using the boundary equations and is compared for the different gap lengths. The accumulated charge density was larger for the smaller gap lengths. Comparing PD parameters with accumulated charge density enabled us to identify that the number of negative and positive PD pulses is the main parameter that corresponds to charge accumulation process.

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  79. Current Limiting Characteristics of Parallel-connected Coated Conductors for High-Tc Superconducting Fault Current Limiting Transformer (HTc-SFCLT) Reviewed International coauthorship International journal

    K. Omura, H. Kojima, N. Hayakawa, F. Endo, M. Noe, H. Okubo

    IEEE Transactions on Applied Superconductivity   Vol. 19 ( 3 ) page: 1880 - 1883   2009.6

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    We have been developing superconducting fault current limiting transformer (SFCLT) as a superconducting transformer with current limiting function. As the step-5 of the SFCLT project for the up-graded ratings of current and voltage, in this paper, we focused on the up-grading of current by parallel-connected YBCO coated conductors. Based on the asymmetric configuration of coated conductors, different parallel connections were tested and evaluated in terms of critical current level and current limiting characteristics under large AC current at 77 K in liquid nitrogen.

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  80. Dynamic Thermal Characteristics of HTS Coil for Conduction-cooled SMES Reviewed International journal

    H. Kojima, X. Chen, N. Hayakawa, F. Endo, H. Okubo

    IEEE Transactions on Applied Superconductivity   Vol. 19 ( 3 ) page: 2036 - 2039   2009.6

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    In this paper, we investigate the thermal runaway characteristics of a BSCCO HTS single pancake coil conduction-cooled with a 4 K-GM cryo-cooler system. We also evaluate the static and dynamic characteristics of the HTS coil by measuring the temporal evolution of the temperature and the voltage for steady current and the typical current patterns of the load fluctuation compensation at different ambient temperatures T0 in the range of 20-50 K. Moreover, we experimentally discuss the criterion for monitoring the conduction-cooled HTS SMES system during compensating operation for load fluctuations.

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  81. Partial Discharge Activity in Electrical Insulation for High Temperature Superconducting (HTS) Cables Reviewed International journal

    H. Okubo, H. Kojima, F. Endo, K. Sahara, R. Yamaguchi, N. Hayakawa

    IEEE Transactions on Dielectrics and Electrical Insulation   Vol. 15 ( 3 ) page: 647 - 654   2008.6

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    This paper discusses electrical insulation characteristics of liquid nitrogen (LN2) / polypropylene (PP) laminated paper composite insulation system for the practical electrical insulation design of high temperature superconducting (HTS) cables. Partial discharge (PD) inception, propagation and breakdown (BD) characteristics under ac voltage application were obtained and discussed at atmospheric and pressurized conditions. Experimental results were analyzed quantitatively and revealed that voidtype discharge was categorized as an important form of discharge to characterize the transition of PD activity leading to BD. © 2008 IEEE.

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  82. Quench-Induced Partial Discharge Characteristics of HTS Cables Reviewed International journal

    N. Hayakawa, S. Ueyama, H. Kojima, F. Endo, Y. Ashibe, T. Masuda, M. Hirose

    Journal of Physics: Conference Series   Vol. 97 ( 1 ) page: 012053   2008.3

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    This paper discusses the partial discharge (PD) characteristics of HTS cables under quench condition, where the thermal stress due to quench would be transiently superposed on the electric field stress under the operating voltage of HTS cables. Such electrical insulation characteristics under thermal/electrical combined stress can be referred to as the "quench-induced PD characteristics" of HTS cables, which should be taken into account for the reliable insulation design of HTS cables. Experimental results using coaxial HTS cable samples revealed that the quench-induced PD could be generated, even under the intrinsic or static PD inception voltage (PDIVsta) without the quench. The criteria of the thermal/electrical combined stress level for quench-induced PD inception were quantified for different LN2 pressures and fault durations under sub-cooled condition. © 2008 IOP Publishing Ltd.

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  83. Self-recovery Characteristics of High-Tc Superconducting Fault Current Limiting Transformer (HTc-SFCLT) with 2G Coated Conductors Reviewed International coauthorship International journal

    H. Kojima, S. Itoh, N. Hayakawa, F. Endo, M. Noe, H. Okubo

    Journal of Physics: Conference Series   Vol. 97 ( 1 ) page: 012154   2008.3

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    We have been developing Superconducting Fault Current Limiting Transformer (SFCLT) with both functions of superconducting transformer and superconducting fault current limiter. As the Step-IV of the SFCLT project, in this paper, we designed, fabricated and tested HTc-SFCLT with 2G YBCO coated conductors to be operated in liquid nitrogen at 77 K. The ratings of the HTc-SFCLT with 2G coated conductors are 3-phase, 100 kVA, 6600 V / 210 V. Especially, the possibility of self-recovery into superconducting state after the fault current limitation was investigated by the simple clearance of the fault, which is very important as a superconducting transformer and for power system operation. The criteria of self-recovery were quantified for different combination of load current before the fault and prospective fault current during the fault. © 2008 IOP Publishing Ltd.

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  84. Breakdown Characteristics of N2O Gas Mixtures for Quasi-uniform Electric Field under Lightning Impulse Voltage Reviewed International journal

    H. Kojima, O. Kinoshita, N. Hayakawa, F. Endo, H. Okubo, M. Yoshida, T. Ogawa

    IEEE Transactions on Dielectrics and Electrical Insulation   Vol. 14 ( 6 ) page: 1492 - 1497   2007.12

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    From the viewpoint of mitigating global warming by SF6 gas, this paper discusses breakdown (BD) characteristics of different electronegative gas mixtures with N2O gas as SF6 gas substitutes for quasi-uniform electric field under lightning impulse voltage applications. Experimental results revealed the positive synergism in breakdown strength of binary N2O / CO2 and ternary N2O / CO 2 / O2 gas mixtures, respectively. Furthermore, N 2 gas as a retardant gas was also mixed with the electronegative gas mixtures in order to reduce the electron energy into the effective levels of electron attachment ability by the electronegative gas mixtures. As the result, ternary N2O /CO2 / N2 and quaternary N 2O / CO2 / O2 / N2 gas mixtures could exhibit the significant synergistic effect in breakdown strength. The optimum mixture rate of quaternary N2O / CO2 / O 2 / N2 gas mixtures was consistent with that estimated by assuming the independent contribution of component gases to the improvement of impulse BD characteristics. © 2007 IEEE.

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  85. Electrical Insulation Characteristics of HTS Cables under Quench-Induced Thermal Stress Condition Reviewed International journal

    N. Hayakawa, S. Ueyama, H. Kojima, F. Endo, T. Masuda, M. Hirose

    IEEE Transactions on Applied Superconductivity   Vol. 17 ( 2 ) page: 1660 - 1663   2007.6

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    This paper discusses the electrical insulation characteristics of high temperature superconducting (HTS) cable under quench condition exposed to thermal and electrical combined stress. We applied a high voltage of 60 Hz ac to the sample electrode, and injected a large current of 60 Hz ac into Bi2223/Ag tapes to induce quench. Experimental results revealed that partial discharges (PD) were induced by the transient thermal stress due to quench under the high voltage condition. A criterion of the combined stress for PD inception was experimentally obtained. © 2007 IEEE.

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  86. Thermal Runaway Characteristics of Bi2212 Coil for Conduction-cooled SMES Reviewed International journal

    H. Kojima, N. Hayakawa, S. Noguchi, F. Endo, N. Hirano, S. Nagaya, H. Okubo

    IEEE Transactions on Applied Superconductivity   Vol. 17 ( 2 ) page: 1959 - 1962   2007.6

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    In this paper, we investigated the thermal runaway characteristics of a conduction-cooled Bi2212 HTS coil with a 4 K-GM cryocooler system under compensating operation for load fluctuations. We measured the temporal evolutions of temperature and voltage distributions of the HTS solenoidal coil for typical current patterns of load fluctuation compensation at different ambient temperatures. On the basis of these experimental results, we constructed a thermal analysis model, and analysed the thermal runaway characteristics during and after the load fluctuation compensation. Based on the results of our experiments and the numerical simulations, we proposed criterion for the monitoring of an HTS SMES system during compensating operation for load fluctuations.

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  87. High-Tc Superconducting Fault Current Limiting Transformer (HTc-SFCLT) with 2G Coated Conductors Reviewed International coauthorship International journal

    H. Okubo, C. Kurupakorn, S. Ito, H. Kojima, N. Hayakawa, F. Endo, M. Noe

    IEEE Transactions on Applied Superconductivity   Vol. 17 ( 2 ) page: 1768 - 1771   2007.6

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    We developed a 3-phase, 100 kVA, 6600 V/210 V high temperature Superconducting Fault Current Limiting Transformer (HTc-SFCLT) with functions of both superconducting transformer and fault current limiter. The HTc-SFCLT is characterized by the application of 2G coated conductors with the higher current limiting performance and flexibility than that of the HTc-SFCLT with 1G Bi2212/CuNi composite bulk material. Fundamental tests of the HTc-SFCLT were carried out, and the design parameters as a superconducting transformer and as a superconducting fault current limiter were verified. © 2007 IEEE.

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  88. Synergy Effect in Electrical Insulation Characteristics of N2O Gas Mixtures Reviewed

    N. Hayakawa, O. Kinoshita, H. Kojima, F. Endo, M. Yoshida, T. Ogawa, H. Okubo

    IEEJ Transactions on Power and Energy   Vol. 126 ( 11 ) page: 1164 - 1170   2006.11

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    This paper discusses partial discharge (PD) and breakdown (BD) characteristics of N<sub>2</sub>O gas and N<sub>2</sub>O gas mixtures as SF<sub>6</sub> substitutes as a function of gas pressure and N<sub>2</sub>O content for quasi-uniform and non-uniform electric field under lightning impulse and ac voltage application. Experimental results revealed the significant positive synergism in breakdown strength of N<sub>2</sub>O30%/CO<sub>2</sub>70% and N<sub>2</sub>O30%/CO<sub>2</sub>50%/O<sub>2</sub>20% gas mixtures under quasi-uniform electric field. Furthermore, corona stabilization effect in N<sub>2</sub>O30%/CO<sub>2</sub>70% gas mixtures under non-uniform electric field was discussed and suggested to be activated due to the combination of electronegative N<sub>2</sub>O and CO<sub>2</sub> gases.

    DOI: 10.1541/ieejpes.126.1164

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  89. Simulation of Electrical and Thermal Behavior of High Temperature Superconducting Fault Current Limiting Transformer (HTc-SFCLT) Reviewed International coauthorship International journal

    C. Kurupakorn, H. Kojima, N. Hayakawa, F. Endo, N. Kashima, S. Nagaya, M. Noe, H. Okubo

    Journal of Physics: Conference Series   Vol. 43   page: 950 - 953   2006.7

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    Superconducting Fault Current Limiting Transformer (SFCLT) is expected to perform functions both of transformer in the normal operating condition and of fault current limiter in the system fault condition. As the Phase-3 of the SFCLT project, we have been developing SFCLT based on Bi2212/CuNi bulk coils at LN2 temperature and verified its technical feasibility. In this paper, we developed a numerical model for evaluation of the electrical and thermal behavior of HTc-SFCLT such as current limitation and recovery characteristics. This model took into account E-J characteristics of Bi2212/CuNi bulk coil and its electrical and thermal transient phenomena during the operation of HTc-SFCLT. The simulated current agreed well with the experimental data with the error of less than 5%. The excellent current limitation and self recovery characteristics obtained by the experiments could also be reproduced. With the numerical model, current and thermal behavior of HTc-SFCLT was simulated for different parameters of conductor configuration, which would be useful for the future design and optimization of HTc-SFCLT. © 2006 IOP Publishing Ltd.

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  90. Electrical and Thermal Characteristics of Bi2212/Ag HTS Coils for Conduction-cooled SMES Reviewed International journal

    N. Hayakawa, S. Noguchi, C. Kurupakorn, H. Kojima, F. Endo, N. Hirano, S. Nagaya, H. Okubo

    Journal of Physics: Conference Series   Vol. 43   page: 813 - 816   2006.7

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    In this paper, we investigated the electrical and thermal performance of conduction-cooled Bi2212/Ag HTS coils with 4K-GM cryocooler system. First, we measured the critical current Ic for different ambient temperatures T0 at 4.2 K - 40 K. Experimental results revealed that Ic increased with the decrease in T0 and was saturated at T0 < 10 K. We carried out thermal analysis considering heat generation, conduction and transfer under conduction-cooling condition, and reproduced the electrical and thermal characteristics of the conduction-cooled HTS coil, taking account of temperature dependence of specific heat and thermal conductivity of the materials. We also measured the temperature rise of Bi2212/Ag HTS coil for different continuous current levels at T0 4.8 K. Experimental results revealed the criterion of thermal runaway, which was discussed in terms of heat generation and propagation in the test coil. © 2006 IOP Publishing Ltd.

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  91. Impulse and AC Partial Discharge Inception and Breakdown Characteristics of LN2/Polypropylene Laminated Paper Composite Insulation System Reviewed International journal

    H. Okubo, H. Kojima, F. Endo, K. Sahara, N. Hayakawa

    IEEE Transactions on Dielectrics and Electrical Insulation   Vol. 13 ( 3 ) page: 664 - 669   2006.6

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    Partial discharge (PD) inception and breakdown (BD) characteristics of liquid nitrogen (LN2) / polypropylene (PP) laminated paper composite insulation system for high temperature superconducting (HTS) cables are presented. In this paper, we measured PD inception characteristics under lightning impulse and ac voltage applications by electrical, optical and acoustic methods. The impulse PD inception characteristics were compared with those under ac voltage application, and the PD generation mechanisms are discussed. Experimental results reveal that PD detection sensitivity under lightning impulse voltage application is as small as 6 pC. PD inception at the lower stress was verified to be generated not only in the butt gaps but also in micro gaps between PP laminated paper layers under both lightning impulse and ac voltage applications. After PD inception, PD activity could be developed in the butt gaps at the higher stress, finally leading to BD. © 2006 IEEE.

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  92. Temperature Dependence of Critical Current at 4.2 K-55 K of Conduction-cooled Bi2212/Ag Wires for SMES Reviewed International journal

    H. Kojima, S. Noguchi, C. Kurupakorn, N. Hayakawa, M. Goto, N. Hirano, S. Nagaya, H. Okubo

    IEEE Transactions on Applied Superconductivity   Vol. 15 ( 2 ) page: 2550 - 2553   2005.6

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    In this paper, fundamental characteristics of conduction-cooled Bi2212/Ag wires and coils for HTS SMES were investigated, in terms of critical current at different temperatures at 4.2 K-55 K. Experimental results revealed that the critical current did not always increase with the temperature decrease, but was saturated or even decreased, depending on the test sample condition. Thermal analysis considering temperature dependence of specific heat and thermal conductivity of the materials could explain the critical current-temperature characteristics, and suggest the possibility to optimize the operating temperature of SMES. © 2005 IEEE.

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  93. Dielectric Characteristics of HTS Cables Based on Partial Discharge Measurement Reviewed International journal

    N. Hayakawa, M. Nagino, H. Kojima, M. Goto, T. Takahashi, K. Yasuda, H. Okubo

    IEEE Transactions on Applied Superconductivity   Vol. 15 ( 2 ) page: 1802 - 1805   2005.6

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    We have discussed dielectric characteristics of liquid nitrogen (LN 2)/polypropylene (PP) laminated paper composite insulation system for the practical electrical insulation design of high temperature superconducting (HTS) cables. Focusing on the partial discharge (PD) inception characteristics and mechanism, the volume effect and its saturation on PD inception electric field strength (PDIE) was evaluated at atmospheric and pressurized condition. PD inception characteristics under lightning impulse voltage application were also investigated using an electrical and optical PD measuring system, and compared with those under ac voltage application. © 2005 IEEE.

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  94. Recovery Characteristics after Current Limitation of High Temperature Superconducting Fault Current Limiting Transformer (HTc-SFCLT) Reviewed International coauthorship International journal

    C. Kurupakorn, H. Kojima, N. Hayakawa, M. Goto, N. Kashima, S. Nagaya, M. Noe, K.-P. Juengst, H. Okubo

    IEEE Transactions on Applied Superconductivity   Vol. 15 ( 2 ) page: 1859 - 1862   2005.6

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    Superconducting Fault Current Limiting Transformer (SFCLT) is one of the promising superconducting power apparatus, since it has both functions of superconducting transformer in normal condition and superconducting fault current limiter in fault condition. In this paper, current limiting and the recovery tests of high temperature SFCLT (HTc-SFCLT) with MCP-BSCCO2212 bulk coils were performed at liquid nitrogen temperature. Experimental results revealed that the HTc-SFCLT could successfully recover into the superconducting state by itself immediately after the fault clearance. Moreover, the recovery criterion of HTc-SFCLT as a function of load current was clarified. © 2005 IEEE.

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  95. Formation of Deep Potential Well and its Structural Transition in Small Tokamak Device International journal

    Y. Fukuzawa, H. Kojima, T. Okada, N. Ohno, S. Takamura

    Europhysics Conference Abstracts   Vol. 28G   page: P-5.075   2004.7

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  96. 小型トカマク放電の高機能化に関する研究 Reviewed

    小島寛樹

    名古屋大学大学院工学研究科博士学位論文   ( 甲第6265号 )   2004.3

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  97. Formation and Dynamics of Very Deep Negative Potential Well in the Small Tokamak Device CSTN-IV Reviewed International journal

    H. Kojima, Y. Fukuzawa, T. Manabe, S. Takamura, T. Okada, N. Ohno

    Czechoslovak Journal of Physics   Vol. 53 ( 10 ) page: 895 - 902   2003.10

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    We achieved a potential well more than fifty times deeper than the plasma electron temperature, down to -0.3 kV with the electrode biasing, by the cross-field radial arcing current of up to 150 A which flows between the small electron-emitting electrode (LaB6)inserted to the plasma center and the stainless-steel wall of vacuum chamber. The empirical scaling of the radial resistance of plasma Rr on the radial arcing current Ib and the toroidal magnetic field BT is found to be Rr ∼ Ib-1.2 BT1.0. Structural dynamics of negative potential well formation is observed: the potential dip propagates from the plasma core to the periphery. The ion saturation current also increases, starting from the inner region. The fluctuation frequency in I sat changes abruptly from 200 kHz to 30 kHz in a time of around 0.25 ms after negative biasing.

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  98. Spatiotemporal Behavior of Hydrogen Recycling due to the Rotating Magnetic Field Reviewed International journal

    H. Kojima, S. Takamura

    Japanese Journal of Applied Physics   Vol. 42 ( 9A ) page: 5797 - 5798   2003.9

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    A rotating helical magnetic field (RHF) moderates the toroidal nonuniformity of plasma particle flux to the wall, and increases effective wall surface area for hydrogen recycling. Employing a one-dimensional numerical modeling, the dynamic response of neutral gas pressure to the external RHF has been analyzed. The fast dynamic behavior is determined by the plasma particle reflection on the wall and the toroidal diffusion of neutrals, while the longer-time dynamic behavior depends more on the absorption of neutrals into the wall.

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  99. Structural Dynamics of Deep Negative Potential Well Formation in Small Tokamak Device CSTN-IV International journal

    H. Kojima, Y. Fukuzawa, T. Manabe, N. Ohno, S. Takamura

    Europhysics Conference Abstracts   Vol. 27A   page: P-2.130   2003.9

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  100. Effects of Rotating Helical Magnetic Field on Inhomogeneities of Hydrogen Recycling in a Tokamak Discharge. Reviewed International journal

    H. Kojima, S. Takamura

    Japanese Journal of Applied Physics   Vol. 41 ( 11A ) page: 6557 - 6562   2002.11

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    A rotating helical magnetic field (RHF) makes an effective recycling wall area increase so that the wall pumping may be enhanced more than that in the absence of RHF by rotating a poloidally periodic edge magnetic field structure. On the other hand, a mitigation of the toroidally asymmetric recycling property due to the RHF has been observed. The reason for such a mitigation of toroidal inhomogeneity comes from the fact that the application of the RHF moderates a toroidal nonuniformity of the plasma flux to the wall while the original plasma-wall interaction is nonuniform toroidally due to a shift of the toroidal plasma loop. Such mitigation is discussed, employing a one-dimensional numerical modeling.

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  101. Characteristics of Local Helical Coil System for Dynamic Ergodic Divertor Invited International journal

    Y. Kikuchi, H. Kojima, T. Taniyama, M. Toyoda, Y. Uesugi, S. Takamura

    Electrical Engineering in Japan   Vol. 139 ( 1 ) page: 16 - 23   2002.4

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    Heat and particle flux control is one of the most important and difficult problems in steady-state fusion devices. The Dynamic Ergodic Divertor (DED) is an advanced concept in which a rotational perturbed magnetic field is applied to make the tokamak edge magnetic structure stochastic so that it may decrease the heat and particle flux onto the local target in the conventional divertor. This rotational perturbed field is created by two sets of local helical coils (LHC) with a phase difference of 90° in the supplied ac currents. In DED experiments, it is important to study the perturbed magnetic field structure generated by these coil currents. In this paper, a new coil configuration is considered, which has an additional series of return windings so as to improve the mode quality of the rotating helical field (RHF). We obtain the mode structure of RHF using a new Fourier analysis. From this result, we confirm that the parasitic mode of RHF and the coil self-inductance are decreased by the new coil configuration. © 2002 Scripta Technica, Electr. Eng. Jpn.

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  102. Toroidal Dependence of Hydrogen Recycling Property with Helical Magnetic Perturbation in Long Time Discharge International journal

    H. Kojima, S. Takamura

    Europhysics Conference Abstracts   Vol. 25A   page: 2129-2132   2001.12

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    Authorship:Lead author, Corresponding author   Language:English   Publishing type:Research paper (international conference proceedings)  

  103. Effects of Dynamic Island Formations on Rotating Helical Magnetic Field Penetration into the Tokamak Plasma International journal

    Y. Kikuchi, H. Kojima, T. Taniyama, M. Toyoda, Y. Uesugi, S. Takamura

    Europhysics Conference Abstracts   Vol. 25A   page: 277-280   2001.12

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  104. Characteristics of Local Helical Coil System for Dynamic Ergodic Divertor Reviewed

    Y. Kikuchi, H. Kojima, T. Taniyama, M. Toyoda, Y. Uesugi, S. Takamura

    IEEJ Transactions on Fundamentals and Materials   Vol. 121 ( 3 ) page: 249 - 255   2001.3

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    Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher:The Institute of Electrical Engineers of Japan  

    Heat and particle flux control is one of the most important and difficult problems in steady state fusion devices. Dynamic Ergodic Divertor (DED) is the advanced concept that a rotational perturbed magnetic field is applied to make tokamak edge magnetic structure stochastic so that it may decrease the heat and particle flux onto the local target in the conventional divertor. This rotational perturbed field is created by two sets of local helical coils (LHC) with the phase difference of 90 degrees in supplied AC currents. For the DED experiment, it is important to know the perturbed magnetic field structure due to this coil currents. We obtain the mode structure of the rotating helical field using a new Fourier analysis so that we may improve the mode quality by employing a new coil configuration which has an addtional series of return windings so as to avoid unnecessary mode and decrease the coil self-inductance.

    DOI: 10.1541/ieejfms1990.121.3_249

    CiNii Research

    J-GLOBAL

  105. Penetration Process of the Externally Applied Rotating Helical Field into the Tokamak Plasma International journal

    M. Kobayashi, H. Kojima, S. Takamura

    Europhysics Conference Abstracts   Vol. 24B   page: 1404-1407   2001.1

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    Language:English   Publishing type:Research paper (international conference proceedings)  

  106. Research Tokamak System with Multimode Discharges Using Inverter Power Supply Invited International journal

    H. Kojima, M. Kobayashi, K. Tashiro, M. Takagi, S. Takamura

    Electrical Engineering in Japan   Vol. 133 ( 4 ) page: 8 - 18   2000.12

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    Authorship:Lead author, Corresponding author   Language:English   Publishing type:Research paper (scientific journal)   Publisher:Wiley Periodicals, LLC.  

    In the Current Sustaining Tokamak of the Nagoya University (CSTN)-IV research tokamak system, using a compact 40-kHz pulse width modulation (PWM) inverter power supply, which is controlled through the LabVIEW program, we construct a new tokamak discharge system with multimode including a stable alternating current discharge and a high-repetition high-duty one. These discharge modes can be operated continuously for as long as 60 seconds. The continuous discharge of long duration is able to simulate the important physical and chemical processes of long discharges in fusion devices, in which the heat load to the wall and the particle balance in the plasma-wall system are crucial topics in order to realize a long pulse fusion reactor, like ITER. An ergodic divertor is one of the tools used to control the particle balance and the heat load to the wall. In addition, we installed another inverter power supply to generate a rotating magnetic perturbation for a dynamic ergodic divertor (DED) with the appropriate measurement system so that we could carry out experiments on heat and particle control with DED in prolonged operation.

    DOI: 10.1002/1520-6416(200012)133:4<8::AID-EEJ2>3.3.CO;2-9

    DOI: 10.1002/1520-6416(200012)133:4<8::AID-EEJ2>3.0.CO;2-I

    Web of Science

    Scopus

  107. Frequency Dependence of Tokamak Plasma Response to the Externally Applied Rotating Helical Field Reviewed International journal

    M. Kobayashi, H. Kojima, K. Zhai, S. Takamura

    Physics of Plasmas   Vol. 7 ( 8 ) page: 3288 - 3300   2000.8

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:AIP Publishing  

    The frequency dependence of the tokamak plasma response to the externally applied rotating helical field was investigated by measuring the radial profile of the perturbation field with small magnetic probes which were inserted in the plasma. The experimental results are discussed, directly comparing with the generally accepted linear theory, and taking into account the EXB drift and diamagnetic effect of the plasma. It was found that the experimental results are in good agreement with the simple linear analysis based on the single helicity approximation in a cylindrical geometry, except for the ergodic region, which comes from the overlapping of several sideband components of the perturbation. It is also found that the radial component of the perturbation field is still amplified inside the resonance surface (r<rs), even when a partial shielding takes place at r ≈rs. © 2000 American Institute of Physics.

    DOI: 10.1063/1.874194

    Web of Science

    Scopus

    J-GLOBAL

  108. Electrostatic Fluctuations in the Current Sustained Torus IV at Nagoya University Reviewed International journal

    K. Zhai, M. Kobayashi, K. Tashiro, H. Kojima, M. Takagi, S. Takamura

    Physics of Plasmas   Vol. 7 ( 6 ) page: 2449 - 2455   2000.6

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:AIP Publishing  

    A detailed experimental investigation of plasma fluctuation and its modification due to radial electric field effects, both its shear and curvature, has been carried out on the Current Sustained Torus IV at Nagoya University [Takamura et al., J. Plasma Fusion Res. 74, 38 (1998)] through measurement with an array of Langmuir probes. The observed statistical dispersion relation indicates a drift-wave-type turbulence. An examination of the radial electric field shear and curvature effects on the fluctuations as well as comparisons to theoretical predictions are presented. The decorrelation of turbulence is found to be influenced by the radial electric field shear in our experiment. A modification of the poloidal correlation length and the two-poloidal-point coherency due to the radial electric field has also been identified. Nonlinear analysis of quadratic mode coupling indicates that the radial electric field can affect the fluctuation amplitudes by modifying the coupling between different spectral components of the fluctuations. © 2000 American Institute of Physics.

    DOI: 10.1063/1.874084

    Web of Science

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    J-GLOBAL

  109. Interaction of Externally Applied Rotating Helical Field with Tokamak Plasma Reviewed International journal

    M. Kobayashi, T. Tuda, K. Tashiro, H. Kojima, K. Zhai, S. Takamura

    Nuclear Fusion   Vol. 40 ( 2 ) page: 181 - 193   2000.2

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:IOP Publishing  

    The penetration process of a rotating magnetic perturbation into a rotating tokamak plasma has been investigated, taking account of the mode structure of the perturbations, and using a small magnetic probe in the small research tokamak CSTN-IV. It was observed that the radial component of the perturbation was amplified in the plasma when magnetic islands are formed, while the poloidal component was attenuated but, deep inside the plasma, amplified. Using a resistive MHD code, such modifications of external perturbation were found to be caused by a redistribution of plasma current due to the formation of magnetic islands. Considering the phase velocity of both the perturbation and the intrinsic plasma rotation, it was also found that the sideband component substantially affects the penetration process with magnetic islands forming. Therefore, in dynamic ergodic divertor operation, it is necessary to put the emphasis not only on the frequency of the perturbation fields but also on their direction, mode structure and the radial profile of the intrinsic plasma rotation at the same time.

    DOI: 10.1088/0029-5515/40/2/304

    Web of Science

    Scopus

    J-GLOBAL

  110. Research Tokamak System with Multi-Mode Discharges Using Inverter Power Supply Reviewed

    H. Kojima, M. Kobayashi, K. Tashiro, M. Takagi, S. Takamura

    IEEJ Transactions on Fundamentals and Materials   Vol. 119 ( 12 ) page: 1436 - 1444   1999.12

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    Authorship:Lead author, Corresponding author   Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher:The Institute of Electrical Engineers of Japan  

    In Current Sustaining Tokamak in Nagoya university (CSTN)-IV research tokamak system using a compact 40kHz pulse width modulation (PWM) inverter power supply, which is controlled through LabVIEW program, we construct a new tokamak discharge system with multi-mode including a stable alternating current discharge and a high-repetition high-duty one. These discharge modes can be operated continuously for as long as 60sec. The continuous discharge with long duration is able to simulate the important physical and chemical processes of long time discharges in fusion devices, in which the heat load to the wall and the particle balance in the plasma-wall system are crucial topics in order to realize a long pulse fusion reactor, like ITER. Employing ergodic divertor (ED) is one of tools to control the particle balance and the heat load to the wall. In addition, we installed another inverter power supply to generate a rotating magnetic perturbation for dynamic ergodic divertor (DED) with the appropriate measurement system so that we may carry out experiments on heat and particle control with DED at long time operation.

    DOI: 10.1541/ieejfms1990.119.12_1436

    CiNii Research

    J-GLOBAL

  111. Experimental Investigation on Penetration of Rotating Magnetic Perturbations into the Tokamak Plasma International journal

    M. Kobayashi, T. Tuda, Z. Kan, H. Kojima, K. Tashiro, S. Takamura

    Europhysics Conference Abstracts   Vol. 23J   page: 437-440   1999.7

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  112. Two-dimensional Structure of the Detached Recombining Helium Plasma Associated with Molecular Activated Recombination Reviewed International coauthorship International journal

    D. Nishijima, N. Ezumi, H. Kojima, N. Ohno, S. Takamura, S. I. Krasheninnikov, A. Yu. Pigarov

    Journal of Nuclear Materials   Vol. 266   page: 1161 - 1166   1999.3

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:Elsevier B.V.  

    The structural change of the detached plasmas associated with the molecular activated recombination (MAR) has been studied in a high density helium plasma with helium or hydrogen puff in the linear divertor plasma simulator, NAGDIS-II. The ion particle flux with the hydrogen gas puff starts to decrease in the upstream region close to the plasma source, compared to that with the helium puff. The reduction of the ion particle flux along the magnetic field is found to depend on the plasma density. With the hydrogen gas puff, the attenuation of the ion particle flux is getting smaller as increasing plasma density, which is opposite tendency in pure helium detached plasma where the conventional electron-ion recombination (EIR) is dominating.

    DOI: 10.1016/S0022-3115(98)00565-0

    Web of Science

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  113. Contribution of Molecular Activated Recombination to Hydrogen Plasma Detachment in the Divertor Plasma Simulator NAGDIS-II Reviewed International coauthorship International journal

    N. Ezumi, D. Nishijima, H. Kojima, N. Ohno, S. Takamura, S. I. Krasheninnikov, A. Yu. Pigarov

    Journal of Nuclear Materials   Vol. 266   page: 337 - 342   1999.3

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:Elsevier B.V.  

    We have performed experiments on detached hydrogen plasmas associated with molecular activated recombination (MAR) in a linear divertor plasma simulator. Reductions of the ion particle flux and heat load to the target plate were clearly observed in hydrogen plasmas with the hydrogen gas puff. Detailed analysis of Balmer series spectra with the Collisional-Radiative Atomic-Molecular data (CRAMD) code shows that MAR mainly appears as a weak dependence of the Balmer series emission intensities on experimental conditions in detached hydrogen plasmas. The plasma conditions necessary to obtain plasma detachment through MAR or EIR (electron ion recombination including the radiative and three-body recombination) in tokamak divertors are also discussed.

    DOI: 10.1016/S0022-3115(98)00533-9

    Web of Science

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  114. High-duty Long-duration Repetitive Tokamak Discharge with Static or Rotating Helical Magnetic Field at the Edge International journal

    S. Takamura, M. Kobayashi, K. Tashiro, H. Kojima, K. Zhai, N. Ohno, M. Y. Ye, Y. Uesugi, M. Takagi

    Europhysics Conference Abstracts   Vol. 22C   page: 722-725   1998.6

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  115. Investigation of Hydrogen Plasma Detachment in the Divertor Plasma Simulator NAGDIS-II International coauthorship International journal

    N. Ezumi, D. Nishijima, H. Kojima, N. Ohno, S. Takamura, S. I. Krasheninnikov, A. Yu. Pigarov

    Europhysics Conference Abstracts   Vol. 22C   page: 7-10   1998.6

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  116. Change in Detached Helium Plasma's Structure Associated with Molecular Activated Recombination International journal

    D. Nishijima, N. Ezumi, H. Kojima, N. Ohno, S. Takamura

    Europhysics Conference Abstracts   Vol. 22C   page: 114-117   1998.6

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    Language:English   Publishing type:Research paper (international conference proceedings)  

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Books 11

  1. Insulation design survay of overhead transimission facilities

    ( Role: Joint editor)

    Electric Technology Research Association  2023.12 

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    Total pages:126   Language:Japanese Book type:Report

  2. Technical Trend of GIS (Gas Insulated Switchgear) for Environmental load reduction

    Investigating R&D committee on Technical Trend of GIS (Gas Insulated Switchgear) for Environmental reduction( Role: Joint editor)

    The Institute of Electrical Engineers of Japan  2023.12 

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    Total pages:61   Language:Japanese Book type:Report

  3. Latest Standards and Future Technology Trends related to Gas Insulated Switchgear (GIS)

    The Investigation R&D Committee on Latest Standards and Future Technology Trend Related to Gas Insulated Switchgear (GIS)( Role: Contributor)

    The Institute of Electrical Engineers of Japan  2021.5 

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    Total pages:98   Language:Japanese Book type:Report

  4. Recent Trend on Diversification of Functions and Properties of Transformer

    Investigating R&D Committee for recent trend on diversification of functions and properties of transformer( Role: Contributor)

    The Institute of Electrical Engineers of Japan  2020.6 

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    Total pages:80   Language:Japanese Book type:Report

  5. Technical trend of applied IT and response to renewable energy as for gas-insulated switchgear

    Technical trends of a gas-insulated switchgear related to technologies needed for enhancing introduction of renewable energy, as well as using information technology( Role: Contributor)

    The Institute of Electrical Engineers of Japan  2020.4 

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    Total pages:66   Language:Japanese Book type:Report

  6. 高電圧絶縁技術 ― 9つの核心技術から学ぶ歴史と将来展望

    電気学会・高電圧電気絶縁技術の歴史調査専門委員会( Role: Contributor ,  2.4節,3.6節,第12章,終章)

    オーム社  2019.12  ( ISBN:978-4-274-22408-9

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    Total pages:360   Language:Japanese Book type:Scholarly book

    Other Link: https://www.amazon.co.jp/dp/4274224082

  7. Trends and Comparative Survey of Transformer Domestic and Overseas Standards

    Investigating R&D Committee of Trends and Comparative Survey of Transformer Domestic and Overseas Standards( Role: Contributor)

    The Institute of Electrical Engineers of Japan  2017.8 

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    Total pages:64   Language:Japanese Book type:Report

  8. (エコトピア科学シリーズ 3) 環境調和型社会のためのエネルギー科学

    名古屋大学未来材料・システム研究所 編( Role: Contributor ,  3.1節)

    コロナ社  2016.1  ( ISBN:978-4-339-06883-2

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    Total pages:238   Language:Japanese Book type:Scholarly book

    Other Link: https://www.amazon.co.jp/dp/4339068837/

  9. Recent trend of technical requirements for aged GIS

    Investigating R&D Committee on "Recent trend of technical requirements for aged GIS"( Role: Contributor)

    The Institute of Electrical Engineers of Japan  2015.5 

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    Total pages:84   Language:Japanese Book type:Report

  10. Recent Trend of Electrical and Acoustic Abnormality Diagnostic Technology for Oil-immersed Transformers

    Investigating R&D Transformer Committee( Role: Contributor)

    The Institute of Electrical Engineers of Japan  2015.3 

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    Total pages:79   Language:Japanese Book type:Report

  11. Superconducting Electric Power Apparatus and Systems toward their High Performance and Multifunctions

    Investigating R&D Committee on Superconducting Electric Power Apparatus and Systems toward their High Performance and Multifunctions( Role: Contributor)

    The Institute of Electrical Engineers of Japan  2013.9 

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    Total pages:83   Language:Japanese Book type:Report

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MISC 29

  1. 国際会議報告 第23回高電圧工学国際会議 II.個別セッション 傾斜材料・ナノコンポジット Invited

    小島寛樹

    放電研究   Vol. 67 ( 1 ) page: 11 - 12   2024.2

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    Authorship:Lead author, Last author, Corresponding author   Language:Japanese   Publishing type:Meeting report   Publisher:放電学会  

  2. Recent Topics on Electrical Discharges, Plasma, and Pulsed Power Technologies Invited

    H. Kojima

    IEEJ Transactions on Fundamentals and Materials   Vol. 144 ( 1 ) page: 10 - 11   2024.1

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    Authorship:Lead author, Last author, Corresponding author   Language:Japanese   Publishing type:Article, review, commentary, editorial, etc. (scientific journal)   Publisher:The Institute of Electrical Engineers of Japan  

    <p>This report introduces recent activities of the Technical Committee on Electrical Discharges, Plasma, and Pulsed Power (EPP). The major research subjects and aims of the technical committee on EPP, and the recent activities of the technical committee, such as technical meetings, international conferences, investigation committees are reported.</p>

    DOI: 10.1541/ieejfms.144.10

    Scopus

    CiNii Research

  3. Outline of Technical Committees in IEEJ: Electrical Discharges, Plasma and Pulsed Power (EPP) Invited

    H. Kojima, T. Sasaki, K. Takahashi, Y. Inada, Y. Nakagawa, Y. Nakano

    Electrical Insulation News in Asia   ( 30 ) page: 4 - 5   2023.12

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    Authorship:Lead author, Corresponding author   Language:English   Publishing type:Article, review, commentary, editorial, etc. (scientific journal)   Publisher:Cooperative Research Committee on EINA Magazine, IEEJ  

  4. Recent R&D Topics on Electrical Discharges, Plasma, and Pulsed Power Technologies Invited

    H. Kojima

    IEEJ Transactions on Fundamentals and Materials   Vol. 143 ( 1 ) page: 10 - 11   2023.1

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    Authorship:Lead author, Last author, Corresponding author   Language:Japanese   Publishing type:Article, review, commentary, editorial, etc. (scientific journal)   Publisher:The Institute of Electrical Engineers of Japan  

    <p>This report introduces recent activities of the Technical Committee on Electrical Discharges, Plasma, and Pulsed Power (EPP). The major research subjects and aims of the technical committee on EPP, and the recent activities of the technical committee, such as technical meetings, international conferences, investigation committees are reported.</p>

    DOI: 10.1541/ieejfms.143.10

    Scopus

    CiNii Research

  5. Outline of Technical Committees in IEEJ: Electrical Discharges, Plasma and Pulsed Power (EPP) Invited

    H. Kojima, T. Sasaki, K. Takahashi, Y. Inada, Y. Nakagawa, Y. Nakano

    Electrical Insulation News in Asia   ( 29 ) page: 5 - 6   2022.12

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    Authorship:Lead author, Corresponding author   Language:English   Publishing type:Article, review, commentary, editorial, etc. (scientific journal)   Publisher:Cooperative Research Committee on EINA Magazine, IEEJ  

  6. 学界情報:8th International Conference on Condition Monitoring and Diagnosis (CMD2020) 報告 Invited

    小島寛樹

    電気学会論文誌B(電力・エネルギー部門誌)   Vol. 141 ( 6 ) page: NL6_3 - NL6_3   2021.6

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    Authorship:Lead author, Last author, Corresponding author   Language:Japanese   Publishing type:Meeting report   Publisher:一般社団法人 電気学会  

    DOI: 10.1541/ieejpes.141.nl6_3

    CiNii Research

  7. 研究グループ 紹介:名古屋大学 大学院工学研究科 電気工学専攻 電力機器・エネルギー伝送工学研究グループ Invited

    早川直樹, 小島寛樹

    電気学会論文誌A(基礎・材料・共通部門誌)   Vol. 141 ( 5 ) page: NL5_6 - NL5_6   2021.5

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    Authorship:Corresponding author   Language:Japanese   Publishing type:Article, review, commentary, editorial, etc. (scientific journal)   Publisher:一般社団法人 電気学会  

    DOI: 10.1541/ieejfms.141.nl5_6

    CiNii Research

  8. Recent Progress in Electrical Discharges, Plasma, and Pulsed Power Technologies

    T. Shirafuji, A. Kumada, H. Kojima, K. Takahashi

    IEEJ Transactions on Fundamentals and Materials   Vol. 140 ( 1 ) page: 10 - 11   2020.1

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    Language:Japanese   Publishing type:Article, review, commentary, editorial, etc. (scientific journal)   Publisher:The Institute of Electrical Engineers of Japan  

    <p>Recent technologies using electrical discharges, plasma, and pulsed power have been used in various areas involving high-voltage electric circuits/machines, organic/inorganic materials processing, environmental protection, biology, medicine, nuclear fusion, propulsion, high-energy particle beams, and high-power electromagnetic wave. This review describes recent progress in electrical discharges, plasma, and pulsed power technologies.</p>

    DOI: 10.1541/ieejfms.140.10

    Scopus

    CiNii Research

  9. 研究調査委員会 レポート:高電圧電気絶縁技術の歴史調査専門委員会

    大久保仁,五島久司,小島寛樹

    電気学会論文誌A(基礎・材料・共通部門誌)   Vol. 139 ( 3 ) page: NL3_4 - NL3_4   2019.3

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    Authorship:Corresponding author   Language:Japanese   Publishing type:Article, review, commentary, editorial, etc. (scientific journal)   Publisher:一般社団法人 電気学会  

    DOI: 10.1541/ieejfms.139.nl3_4

    CiNii Research

  10. Dynamic Breakdown Characteristics of Pancake Coil Model for Resistive Superconducting Fault Current Limiters International journal

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

    IEEE CSC & ESAS Superconductivity News Forum   Vol. 13 ( 46 ) page: STP630   2019.2

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    Language:English   Publishing type:Research paper, summary (international conference)  

  11. 電気分野の人材確保は10年の計 Invited

    小島寛樹

    電気協会報   ( 1084 ) page: 2   2018.7

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    Authorship:Lead author, Last author, Corresponding author   Language:Japanese   Publishing type:Article, review, commentary, editorial, etc. (other)   Publisher:日本電気協会  

  12. 国際会議報告 2017年 第20回高電圧工学国際会議 Invited

    日髙邦彦, 屋地康平, 脇本隆之, 宮嵜悟, 山納康, 岩渕大行, 梅本貴弘, 小島寛樹, 岡部成光, 稲田優貴, 佐藤正寛, 海永壮一朗, 高橋紹大

    放電研究   Vol. 61 ( 1 ) page: 1 - 28   2018.3

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    Language:Japanese   Publishing type:Meeting report   Publisher:放電学会  

  13. いつ電気が苦手になるのか? Invited

    小島寛樹

    パワーアカデミー 研究者コラム   Vol. 25   2016.7

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    Authorship:Lead author, Last author, Corresponding author   Language:Japanese   Publishing type:Article, review, commentary, editorial, etc. (trade magazine, newspaper, online media)   Publisher:パワーアカデミー  

  14. 学界情報:18th International Symposium on High Voltage Engineering (ISH 2013) 報告 Invited

    小島寛樹

    電気学会論文誌B(電力・エネルギー部門誌)   Vol. 134 ( 2 ) page: NL2_3 - NL2_3   2014.2

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    Authorship:Lead author, Last author, Corresponding author   Language:Japanese   Publishing type:Meeting report   Publisher:一般社団法人 電気学会  

    DOI: 10.1541/ieejpes.134.nl2_3

    CiNii Research

  15. 特集2「国際会議報告」 第18回高電圧工学国際会議(ISH2013) 2.セッション報告 Topic F-1 Invited

    小島寛樹

    放電研究   Vol. 56 ( 3 ) page: 42 - 43   2013.11

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    Authorship:Lead author, Last author, Corresponding author   Language:Japanese   Publishing type:Meeting report   Publisher:放電学会  

  16. 次世代科学技術を担う青少年に科学・電気のおもしろさを —東海地区学協会・団体共同による子ども向け科学教室—

    小島寛樹

    電気学会誌   Vol. 133 ( 6 ) page: 372 - 372   2013.6

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    Authorship:Lead author, Last author, Corresponding author   Language:Japanese   Publishing type:Article, review, commentary, editorial, etc. (scientific journal)   Publisher:一般社団法人 電気学会  

    DOI: 10.1541/ieejjournal.133.372

    CiNii Research

  17. 高レベル放射性廃棄物の地層処分に向けた技術開発 —(独) 日本原子力研究開発機構 瑞浪超深地層研究所—

    小島寛樹

    電気学会誌   Vol. 133 ( 1 ) page: 41 - 41   2013.1

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    Authorship:Lead author, Last author, Corresponding author   Language:Japanese   Publishing type:Article, review, commentary, editorial, etc. (scientific journal)   Publisher:一般社団法人 電気学会  

    DOI: 10.1541/ieejjournal.133.41

    CiNii Research

  18. 電力系統の保守と潮流の信頼性を確保する新しい概念「IGMS」

    花井正広,小島寛樹,早川直樹,大久保仁

    OHM   Vol. 99 ( 9 ) page: 4-5   2012.9

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    Language:Japanese   Publishing type:Article, review, commentary, editorial, etc. (trade magazine, newspaper, online media)   Publisher:オーム社  

  19. 特集「国際会議報告」 第17回高電圧工学国際会議(ISH2011) D. High voltage measuring techniques: dielectric parameter, space charges, partial discharges Invited

    小島寛樹,熊田亜希子,岡部成光

    放電研究   Vol. 54 ( 3 ) page: 11 - 15   2011.11

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    Language:Japanese   Publishing type:Meeting report   Publisher:放電学会  

  20. 調査研究委員会レポート:超電導電力機器とシステムの高性能・多機能化調査専門委員会

    小島寛樹

    電気学会論文誌B(電力・エネルギー部門誌)   Vol. 131 ( 10 ) page: NL10_5   2011.10

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    Authorship:Lead author, Last author, Corresponding author   Language:Japanese   Publishing type:Article, review, commentary, editorial, etc. (scientific journal)   Publisher:一般社団法人 電気学会  

    DOI: 10.1541/ieejpes.131.nl10_5

    CiNii Research

  21. 学界情報:International Conference on High Voltage Engineering and Application 2010 (ICHVE2010) 報告 Invited

    小島寛樹

    電気学会論文誌B(電力・エネルギー部門誌)   Vol. 131 ( 4 ) page: 398 - 398   2011.4

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    Authorship:Lead author, Last author, Corresponding author   Language:Japanese   Publishing type:Meeting report   Publisher:一般社団法人 電気学会  

    DOI: 10.1541/ieejpes.131.398

    CiNii Research

  22. Current Limiting and Recovery Characteristics of 2 MVA Class Superconducting Fault Current Limiting Transformer (SFCLT) International journal

    H. Kojima, M. Kotari, T. Kito, N. Hayakawa, M. Hanai, H. Okubo

    IEEE/CSC & ESAS European Superconductivity News Forum   ( 15 ) page: 3LZ-05(ST220)   2011.1

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    Authorship:Lead author, Corresponding author   Language:English   Publishing type:Research paper, summary (international conference)  

  23. 超電導限流変圧器(SFCLT)の開発

    大久保仁,早川直樹,小島寛樹

    OHM   Vol. 97 ( 8 ) page: 2-3   2010.8

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    Authorship:Corresponding author   Language:Japanese   Publishing type:Article, review, commentary, editorial, etc. (trade magazine, newspaper, online media)   Publisher:オーム社  

  24. Development of 2MVA Class Superconducting Fault Current Limiting Transformer (SFCLT) with YBCO Coated Conductors International coauthorship International journal

    M. Kotari, K. Omura, H. Kojima, N. Hayakawa, F. Endo, M. Noe, H. Okubo

    IEEE/CSC & ESAS European Superconductivity News Forum   ( 11 ) page: ST141   2010.1

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    Language:English   Publishing type:Research paper, summary (international conference)  

  25. Partial Discharge Activities under AC/Impulse Superimposed Voltage in LN2/Polypropylene Laminated Paper Insulation System for HTS Cables International journal

    N. Hayakawa, R. Yamaguchi, Y. Ukai, H. Kojima, F. Endo, H. Okubo

    IEEE/CSC & ESAS European Superconductivity News Forum   ( 11 ) page: ST179   2010.1

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    Language:English   Publishing type:Research paper, summary (international conference)  

  26. 特集「国際会議報告」 第16回高電圧工学国際会議(ISH2009) C. HV Insulation Invited

    武田敏信,星野俊弘,伊藤隆史,小島寛樹

    放電研究   Vol. 52 ( 3 ) page: 10 - 13   2009.11

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    Language:Japanese   Publishing type:Meeting report   Publisher:放電学会  

  27. Current Limiting Characteristics of Parallel-connected Coated Conductors for High-Tc Superconducting Fault Current Limiting Transformer (HTc-SFCLT) International coauthorship International journal

    K. Omura, H. Kojima, N. Hayakawa, F. Endo, M. Noe, H. Okubo

    IEEE/CSC & ESAS European Superconductivity News Forum   ( 6 ) page: ST70   2008.10

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    Language:English   Publishing type:Research paper, summary (international conference)  

  28. 国際会議報告2:第15回高電圧工学国際会議 2.セッション報告 トピックス3 新高電圧技術、新材料、界面現象 Invited

    小島寛樹

    放電研究   Vol. 50 ( 3 ) page: 33 - 33   2007.11

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    Authorship:Lead author, Last author, Corresponding author   Language:Japanese   Publishing type:Meeting report   Publisher:放電学会  

  29. The Challenge to a New Research Field Invited

    H. Kojima

    Journal of the Institute of Electrostatics Japan   Vol. 28 ( 4 ) page: 232   2004.8

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    Authorship:Lead author, Last author, Corresponding author   Language:Japanese   Publishing type:Article, review, commentary, editorial, etc. (scientific journal)   Publisher:The Institute of Electrostatics Japan  

    CiNii Research

▼display all

Presentations 762

  1. 交流電圧印加による真空中固体絶縁物上の正帯電形成過程

    杉浦拓真,窪田愛斗,小島寛樹,道念大樹,山口信一,早川直樹

    令和6年電気学会全国大会  2024.3.16  電気学会

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    Event date: 2024.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:徳島大学 常三島キャンパス   Country:Japan  

  2. セルロースナノファイバー(CNF)成形板の部分放電および絶縁破壊電界の厚さ依存性

    木村啓韻,北直樹,小島寛樹,早川直樹,岩永拓実,山下優,岡本徹志,古田尚,奥村浩史,山中雄太

    令和6年電気学会全国大会  2024.3.14  電気学会

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    Event date: 2024.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:徳島大学 常三島キャンパス   Country:Japan  

  3. 超電導限流器が導入された多端子直流送電システムの限流協調

    西澤大将,小島寛樹,早川直樹

    令和6年電気学会全国大会  2024.3.16  電気学会

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    Event date: 2024.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:徳島大学 常三島キャンパス   Country:Japan  

  4. 電動推進航空機用モータ絶縁に適用する流動潤滑油の絶縁破壊特性

    中澤尚輝,野口真平,小島寛樹,有賀信雄,卯辰清志,渡邉瞬也,早川直樹

    令和6年電気学会全国大会  2024.3.16  電気学会

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    Event date: 2024.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:徳島大学 常三島キャンパス   Country:Japan  

  5. アルミ箔/油浸紙複合絶縁系における部分放電による油浸紙損傷と絶縁破壊

    林恭平,神野裕亮,永木雄也,小島寛樹,吉田昌展,早川直樹

    令和6年電気学会全国大会  2024.3.14  電気学会

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    Event date: 2024.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:徳島大学 常三島キャンパス   Country:Japan  

  6. 直流GIS/GIL用σ-FGM絶縁スペーサの乾燥空気中におけるフラッシオーバ特性

    杉本遼次,小島寛樹,早川直樹

    令和6年電気学会全国大会  2024.3.14  電気学会

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    Event date: 2024.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:徳島大学 常三島キャンパス   Country:Japan  

  7. 真空中インパルス絶縁破壊時における陽極表面からの金属粒子の飛散

    北直樹,上野楓真,小島寛樹,福田英昭,山村健太,早川直樹

    令和6年電気学会全国大会  2024.3.14  電気学会

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    Event date: 2024.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:徳島大学 常三島キャンパス   Country:Japan  

  8. 真空中高周波交流コンディショニングの絶縁耐力向上効果における電極材料依存性

    小名木良太,小島寛樹,飯塚伸介,小林将人,早川直樹

    令和6年電気学会全国大会  2024.3.14  電気学会

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    Event date: 2024.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:徳島大学 常三島キャンパス   Country:Japan  

  9. 油浸紙絶縁系のコンデンサ形計器用変圧器における部分放電進展・絶縁破壊メカニズム

    永木雄也,林恭平,神野裕亮,小島寛樹,吉田昌展,早川直樹

    電気学会誘電・絶縁材料/放電・プラズマ・パルスパワー/高電圧合同研究会  2024.1.20  電気学会誘電・絶縁材料/放電・プラズマ・パルスパワー/高電圧技術委員会

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    Event date: 2024.1

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:湯布郷館   Country:Japan  

  10. Fabrication and Flashover Characteristics of Permittivity and Conductivity Graded Materials (ε/σ-FGM) for DC-GIS Spacers International conference

    R. Sugimoto, T. Kato, H. Kojima, N. Hayakawa

    2023 International Symposium on Electrical Insulating Materials  2023.9.25  IEEJ Technical Committee on Dielectrics and Electrical Insulation

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    Event date: 2023.9

    Language:English   Presentation type:Oral presentation (general)  

    Venue:Matsue   Country:Japan  

    The progressive development of HVDC transmission system has urged us to develop a novel technique in supporting the performance of DC power apparatus. Functionally Graded Materials (FGM) are one of the techniques that allow us to control the electric field distribution within the DC insulation system. Our previous works have analytically revealed that FGM with spatial permittivity ε and conductivity σ distributions applied to a 320 kV DC-GIS spacer could reduce the maximum electric field under all DC operating conditions. In this paper, we fabricated a cone-type ε/σ-FGM spacer for DC-GIS and experimentally verified its flashover voltage improvement effect.

    DOI: 10.23919/ISEIM60444.2023.10329009

    Scopus

  11. 放電・プラズマ・パルスパワー分野における研究・技術開発の歩み今後の展望 Invited

    小島寛樹,佐々木徹,高橋克幸,稲田優貴,中川雄介,中野裕介

    令和5年電気学会基礎・材料・共通部門大会  2023.9.8  電気学会基礎・材料・共通部門

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    Event date: 2023.9

    Language:Japanese   Presentation type:Symposium, workshop panel (nominated)  

    Venue:愛知工業大学 自由ヶ丘キャンパス   Country:Japan  

  12. 回転機絶縁システムへの適用を目指したセルロースナノファイバー複合体の基礎特性

    岩永拓実,山下優,岡本徹志,小島寛樹,早川直樹,古田尚,奥村浩史,安食厚志,山中雄太,梅本貴弘

    令和5年電気学会基礎・材料・共通部門大会  2023.9.9  電気学会基礎・材料・共通部門

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    Event date: 2023.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:愛知工業大学 自由ヶ丘キャンパス   Country:Japan  

  13. 真空中沿面放電の初期進展過程における電子軌道追跡による過渡帯電・発光特性

    杉浦拓真,小島寛樹,早川直樹,中野裕介

    令和5年電気学会基礎・材料・共通部門大会  2023.9.7  電気学会基礎・材料・共通部門

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    Event date: 2023.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:愛知工業大学 自由ヶ丘キャンパス   Country:Japan  

  14. DC-GIS用ε/σ-FGMスペーサの作製および直流耐圧向上効果

    杉本遼次,加藤拓夢,小島寛樹,早川直樹

    令和5年電気学会電力・エネルギー部門大会  2023.9.6  電気学会電力・エネルギー部門

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    Event date: 2023.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:愛知工業大学 八草キャンパス   Country:Japan  

  15. 高融点陰極表面への低融点陽極材料の付着による真空中コンディショニング効果の抑制

    北直樹,小島寛樹,福田英昭,山村健太,早川直樹

    令和5年電気学会電力・エネルギー部門大会  2023.9.6  電気学会電力・エネルギー部門

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    Event date: 2023.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:愛知工業大学 八草キャンパス   Country:Japan  

  16. 真空中高周波交流コンディショニングにおける耐圧向上効果の周波数および印加電圧依存性

    小名木良太,小島寛樹,飯塚伸介,小林将人,早川直樹

    令和5年電気学会電力・エネルギー部門大会  2023.9.6  電気学会電力・エネルギー部門

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    Event date: 2023.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:愛知工業大学 八草キャンパス   Country:Japan  

  17. Temperature Rise in Conductivity Graded Materials (σ-FGM) Spacer for HVDC GIS/GIL International conference

    Rachmawati, H. Kojima, N. Hayakawa, H. Okubo

    23rd International Symposium on High Voltage Engineering  2023.8.29  The Department of Electronic and Electrical Engineering of the University of Strathclyde

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    Event date: 2023.8 - 2023.9

    Language:English   Presentation type:Oral presentation (general)  

    Venue:Glasgow   Country:United Kingdom  

  18. Flashover Voltage of Permittivity Graded Materials (ε-FGM) Spacer with Metallic Particles in SF6 Gas International conference

    N. Hayakawa, H. Kato, T. Kato, H. Kojima, S. Kamohara, Y. Hoshina

    23rd International Symposium on High Voltage Engineering  2023.8.29  The Department of Electronic and Electrical Engineering of the University of Strathclyde

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    Event date: 2023.8 - 2023.9

    Language:English   Presentation type:Poster presentation  

    Venue:Glasgow   Country:United Kingdom  

  19. Non-destructive Measurement of Permittivity Distribution in Permittivity Graded Materials (ε-FGM) by X-ray Computed Tomography International conference

    N. Hayakawa, T. Kato, H. Kojima, H. Yanase, K. Okamoto

    23rd International Symposium on High Voltage Engineering  2023.8.29  The Department of Electronic and Electrical Engineering of the University of Strathclyde

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    Event date: 2023.8 - 2023.9

    Language:English   Presentation type:Oral presentation (general)  

    Venue:Glasgow   Country:United Kingdom  

  20. 多端子直流送電システムの超電導限流器動作時における液体窒素の動的絶縁破壊電界の推定

    西澤大将,小島寛樹,早川直樹

    令和五年度電気・電子・情報関係学会東海支部連合大会  2023.8.28  電気学会東海支部,電子情報通信学会東海支部,情報処理学会東海支部,照明学会東海支部,映像情報メディア学会東海支部,日本音響学会東海支部,IEEE名古屋支部

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    Event date: 2023.8

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:豊橋技術科学大学   Country:Japan  

  21. 真空中コンディショニングにおけるギャップ長と最適放電電荷量の関係

    北直樹,小島寛樹,福田英昭,山村健太,早川直樹

    令和五年度電気・電子・情報関係学会東海支部連合大会  2023.8.29  電気学会東海支部,電子情報通信学会東海支部,情報処理学会東海支部,照明学会東海支部,映像情報メディア学会東海支部,日本音響学会東海支部,IEEE名古屋支部

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    Event date: 2023.8

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:豊橋技術科学大学   Country:Japan  

  22. 真空中高周波交流コンディショニングにおける多重絶縁破壊の時間間隔の印加電圧依存性

    小名木良太,小島寛樹,飯塚伸介,小林将人,早川直樹

    令和五年度電気・電子・情報関係学会東海支部連合大会  2023.8.29  電気学会東海支部,電子情報通信学会東海支部,情報処理学会東海支部,照明学会東海支部,映像情報メディア学会東海支部,日本音響学会東海支部,IEEE名古屋支部

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    Event date: 2023.8

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:豊橋技術科学大学   Country:Japan  

  23. 真空中沿面放電の初期進展過程における絶縁物表面への電界入射方向と2次電子なだれの関係

    杉浦拓真,小島寛樹,早川直樹

    令和五年度電気・電子・情報関係学会東海支部連合大会  2023.8.29  電気学会東海支部,電子情報通信学会東海支部,情報処理学会東海支部,照明学会東海支部,映像情報メディア学会東海支部,日本音響学会東海支部,IEEE名古屋支部

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    Event date: 2023.8

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:豊橋技術科学大学   Country:Japan  

  24. 電動推進航空機用モータ絶縁に適用する潤滑油の絶縁破壊特性の流量依存性

    中澤尚輝,小島寛樹,有賀信雄,卯辰清志,渡邉瞬也,早川直樹

    令和五年度電気・電子・情報関係学会東海支部連合大会  2023.8.29  電気学会東海支部,電子情報通信学会東海支部,情報処理学会東海支部,照明学会東海支部,映像情報メディア学会東海支部,日本音響学会東海支部,IEEE名古屋支部

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    Event date: 2023.8

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:豊橋技術科学大学   Country:Japan  

  25. ε/σ-FGM(誘電率/導電率傾斜機能材料)による直流GIS用絶縁スペーサのフラッシュオーバ電圧向上効果

    杉本遼次,小島寛樹,早川直樹

    令和五年度電気・電子・情報関係学会東海支部連合大会  2023.8.29  電気学会東海支部,電子情報通信学会東海支部,情報処理学会東海支部,照明学会東海支部,映像情報メディア学会東海支部,日本音響学会東海支部,IEEE名古屋支部

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    Event date: 2023.8

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:豊橋技術科学大学   Country:Japan  

  26. アルミ箔/油浸紙複合絶縁系における部分放電特性のアルミ箔電極ズレ幅依存性

    林恭平,永木雄也,小島寛樹,吉田昌展,早川直樹

    令和五年度電気・電子・情報関係学会東海支部連合大会  2023.8.29  電気学会東海支部,電子情報通信学会東海支部,情報処理学会東海支部,照明学会東海支部,映像情報メディア学会東海支部,日本音響学会東海支部,IEEE名古屋支部

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    Event date: 2023.8

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:豊橋技術科学大学   Country:Japan  

  27. Electrode Material Adhesion between Anode and Cathode in Spark Conditioning in Vacuum International conference

    N. Kita, H. Kojima, H. Fukuda, K. Yamamura, N. Hayakawa

    30th International Symposium on Discharge and Electrical Insulation in Vacuum  2023.6.26  Technical Committee of Electrical Dicharges, Plasma and Pulsed Power, IEEJ

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    Event date: 2023.6

    Language:English   Presentation type:Oral presentation (general)  

    Venue:Okinawa   Country:Japan  

    We discuss the electrode material adhesion between cathode and anode during spark conditioning process in vacuum, and its effect on dielectric strength in terms of breakdown (BD) charge. We focus on the conditioning effects under rod-plane electrodes with different combination of electrode materials. The material of the rod (cathode) is Cu and that of the plane (anode) is stainless steel (SUS), and their gap length is 1 mm. We observe the electrode surface before and after conditioning experiments. As a result, when BD charge is smaller than 2.0 mC, the anode material (SUS) is found on the cathode (Cu) surface and the dielectric strength becomes high. With increasing BD charge, the adhesion ratio of anode material on the cathode surface decreases, and the dielectric strength also tends to decrease. In the case where BD charge is larger than 2.0 mC, on the contrary, the cathode material (Cu) adheres to the anode (SUS) surface and the dielectric strength is low, which is consistent with the conditioning characteristics when both the cathode and anode are made of Cu. These results indicate that up to a certain BD charge, the anode material adheres to the cathode surface, and above this BD charge the cathode material adheres to the anode surface. When the cathode (Cu) surface is excessively melted, i.e., damaged, the cathode material Cu can adhere to the anode SUS surface. In other words, too large BD charge can not only fails to improve the dielectric strength due to the adhesion of the anode material SUS to the cathode Cu surface, but also causes a critical decrease in the dielectric strength, or deconditioning.

    DOI: 10.23919/ISDEIV55268.2023.10201112

    Scopus

  28. Multiple Breakdown Induced by Previous Breakdown in Higher Frequency AC Conditioning International conference

    R. Konagi, H. Kojima, S. Iitsuka, M. Kobayashi, N. Hayakawa

    30th International Symposium on Discharge and Electrical Insulation in Vacuum  2023.6.29  Technical Committee of Electrical Dicharges, Plasma and Pulsed Power, IEEJ

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    Event date: 2023.6

    Language:English   Presentation type:Poster presentation  

    Venue:Okinawa   Country:Japan  

    We have confirmed that the multiple breakdowns (BDs) occur in a half cycle of AC voltage application in the AC conditioning process in vacuum. In previous research, it has been experimentally confirmed that the higher frequency AC conditioning suppresses the multiple BDs and improves the conditioning effect. In this paper, we discuss how the multiple BDs are induced. By the BD light emission images during AC conditioning, we found that the multiple BDs occurred in close to the previous BD position. This suggests that the multiple BDs were induced by the previous BD. Two possible causes of the multiple BDs are investigated: (a) metal vapor generated by the previous BD and (b) metal particles generated by the previous BD. The diffusion time of metal vapor is much shorter than the time interval for the multiple BDs. Therefore, the multiple BDs may not be induced by metal vapor. On the other hand, for particles of 10 μm order in diameter, the time of collision to the counter electrode matches the time interval of the multiple BDs. Particles of the order of 10 μm in diameter were found on the electrode surface after AC conditioning. These results suggest that the multiple BDs were initiated by metal particles generated by the previous BD and do not contribute to protrusion melting, but damage the electrode surface. Therefore, the higher frequency AC conditioning to suppress the multiple or harmful BDs can be promising for AC conditioning process in vacuum.

    DOI: 10.23919/ISDEIV55268.2023.10201218

    Scopus

  29. Applicability of Lubricating Oil Insulation in Higher Power Density Motors for Electric Powered Aircraft International conference

    N. Hayakawa, H. Kamada, H. Kojima, N. Aruga, K. Utatsu, S. Watanabe

    22nd IEEE International Conference on Dielectric Liquids  2023.6.27  IEEE DEIS

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    Event date: 2023.6

    Language:English   Presentation type:Oral presentation (general)  

    Venue:Worcester   Country:United States  

    Higher power density motors for electric powered aircraft require higher voltage. The authors aim to apply a lubricating oil used for cooling motor windings to an insulating material to improve the dielectric strength of motors. In motor insulation, it is required to prevent the occurrence of partial discharge (PD) and understand the insulating characteristics of the lubricating oil. In this paper, we first measured and compared the breakdown voltage (BDV) of the lubricating oil and mineral oil in a fundamental sphere-sphere electrode system, and discussed the basic breakdown characteristics. The results suggest that the lubricating oil has superior dielectric characteristics to the mineral oil. Next, PD inception voltage (PDIV) of an arrow pair of enamel-coated rectangular wires in the lubricating oil was measured and compared with the estimated PDIV by electric field analysis. As a result, the measured PDIV was generally consistent with the estimated PDIV. Therefore, the lubricating oil insulation is expected to improve the dielectric strength in the motor windings for electric powered aircraft.

    DOI: 10.1109/ICDL59152.2023.10209296

    Scopus

  30. 多端子直流送電システムの線路故障時における超電導限流器の限流効果および過渡安定度向上効果

    村上雅紀,西澤大将,小島寛樹,早川直樹

    令和5年電気学会全国大会  2023.3.17  電気学会

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    Event date: 2023.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:名古屋大学 東山キャンパス   Country:Japan  

  31. 電子追跡シミュレーションによる真空中沿面放電の初期進展メカニズム

    杉浦拓真,小島寛樹,早川直樹

    令和5年電気学会全国大会  2023.3.16  電気学会

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    Event date: 2023.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:名古屋大学 東山キャンパス   Country:Japan  

  32. 電動推進航空機用モータにおける流動潤滑油の部分放電開始特性

    鎌田泰任,中澤尚輝,小島寛樹,有賀信雄,卯辰清志,渡邉瞬也,早川直樹

    令和5年電気学会全国大会  2023.3.15  電気学会

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    Event date: 2023.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:名古屋大学 東山キャンパス   Country:Japan  

  33. コンデンサ形計器用変圧器におけるアルミ箔/油浸紙複合絶縁系の部分放電特性

    林恭平,永木雄也,小島寛樹,吉田昌展,早川直樹

    令和5年電気学会全国大会  2023.3.15  電気学会

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    Event date: 2023.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:名古屋大学 東山キャンパス   Country:Japan  

  34. 真空中コンディショニングの放電電荷量依存性における電極初期表面状態の影響

    北直樹,小島寛樹,福田英昭,山村健太,早川直樹

    令和5年電気学会全国大会  2023.3.15  電気学会

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    Event date: 2023.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:名古屋大学 東山キャンパス   Country:Japan  

  35. 真空中交流コンディショニングにおける粒子起因による多重絶縁破壊

    小名木良太,小島寛樹,飯塚伸介,小林将人,早川直樹

    令和5年電気学会全国大会  2023.3.15  電気学会

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    Event date: 2023.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:名古屋大学 東山キャンパス   Country:Japan  

  36. 乾燥空気中におけるコーン型ε-FGMスペーサの絶縁破壊特性

    加藤拓夢,杉本遼次,小島寛樹,柳瀬博雅,岡本健次,早川直樹

    令和5年電気学会全国大会  2023.3.17  電気学会

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    Event date: 2023.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:名古屋大学 東山キャンパス   Country:Japan  

  37. コンデンサ形計器用変圧器の期待寿命評価方法および部分放電進展特性

    永木雄也,林恭平,小島寛樹,吉田昌展,早川直樹

    電気学会静止器研究会  2022.12.15  電気学会静止器技術委員会

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    Event date: 2022.12

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:Web   Country:Japan  

    Other Link: https://cir.nii.ac.jp/crid/1520858054386646272

  38. Application of TEV Sensors to PD Measurement for Capacitor Voltage Transformers International conference

    Y. Nagaki, H. Kojima, M. Yoshida, N. Hayakawa

    9th International Conference on Condition Monitoring and Diagnosis  2022.11.16  IEEJ Technical Committee on Dielectrics and Electrical Insulation

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    Event date: 2022.11

    Language:English   Presentation type:Oral presentation (general)  

    Venue:Kitakyushu   Country:Japan  

    This study aims to establish an insulation diagnosis method based on partial discharge (PD) measurement for capacitor voltage transformers (CVTs). Since aged CVTs over 50 years have been used in substations, an insulation diagnosis technique for CVTs is urgently required. Recently, transient earth voltage (TEV) sensors are used as PD detection sensors in transformers. Since the TEV sensors detect leakage electromagnetic waves and ground line currents, the PD signals in CVTs can also be detected by TEV sensors. However, the applicability of a TEV sensor to PD measurement in CVTs has not been verified. In this paper, the applicability of a TEV sensor for PD detection in the actual CVT (24-year-old) is discussed. As the experimental results, it was found that the TEV output has a good correlation with the PD charge over a wide range from 60 pC to 60,000 pC with the correlation coefficient as high as 0.99. Therefore, the TEV sensor is effective as a PD sensor for CVTs.

    DOI: 10.23919/CMD54214.2022.9991361

    Scopus

    Other Link: https://www.webofscience.com/api/gateway?GWVersion=2&SrcApp=iroffice_5964&SrcAuth=WosAPI&KeyUT=WOS:000937794300036&DestLinkType=FullRecord&DestApp=WOS_CPL

  39. Partial Discharge Characteristics of Aluminum Foil/Oil-impregnated Paper Insulation System for Insulation Diagnosis of Capacitor Voltage Transformers International conference

    K. Hayashi, S. Wakita, Y. Nagaki, H. Kojima, M. Yoshida, N. Hayakawa

    9th International Conference on Condition Monitoring and Diagnosis  2022.11.17  IEEJ Technical Committee on Dielectrics and Electrical Insulation

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    Event date: 2022.11

    Language:English   Presentation type:Poster presentation  

    Venue:Kitakyushu   Country:Japan  

    Capacitor voltage transformers (CVTs) composed of aluminum foil/oil-impregnated paper insulation system have been operated over 30 years in substations. For the condition monitoring and diagnosis of aged CVTs, partial discharge (PD) detection is expected. However, PD characteristics from PD inception and progress to breakdown (BD) have not yet been clarified. Thus, PD characteristics of a fundamental insulation model composed of aluminum foil/oil-impregnated paper insulation systems are discussed in this paper. Experimental results under a fixed applied voltage revealed that PD characteristics can be classified into 3 periods. In Period 1, PD signals were intermittently generated mainly around the peak phase of applied voltage. In Period 2, PD signals were continuously generated around zero crossing (void discharge) to peak phase. In Period 3, PD signals larger than 10,000 pC were generated. Together with the above electrical PD measurement, the optical measurement of PD light emission images, bubble behavior, and their time transmission were also carried out in order to discuss the mechanism of PD progress.

    DOI: 10.23919/CMD54214.2022.9991513

    Scopus

    Other Link: https://www.webofscience.com/api/gateway?GWVersion=2&SrcApp=iroffice_5964&SrcAuth=WosAPI&KeyUT=WOS:000937794300118&DestLinkType=FullRecord&DestApp=WOS_CPL

  40. Discharge Developing Time of Surface Flashover on Solid Dielectrics around Impulse Test Voltage of Vacuum Interrupters International conference

    R. Watarai, H. Kojima, T. Donen, S. Yamaguchi, N. Hayakawa

    9th International Conference on Condition Monitoring and Diagnosis  2022.11.15  IEEJ Technical Committee on Dielectrics and Electrical Insulation

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    Event date: 2022.11

    Language:English   Presentation type:Poster presentation  

    Venue:Kitakyushu   Country:Japan  

    We have found that the developing time Td of surface flashover on solid dielectrics (alumina) in vacuum is dominated by the propagation time of the conductive channel, which is proportional to the discharge path length and inversely proportional to the square of the discharge inception voltage Vd. Based on the experimental database on Td-Vd characteristics below 30 kV, we have proposed a non-optical diagnostic method for the discharge type and its path length of vacuum interrupters (VI). In this paper, we extend the Td-Vd characteristics up to 100 kV, which is close to the impulse test voltage of VI at 6.6 kV class. Experimental results for different experimental systems and electrode configurations have revealed that at low voltages (Vd < 30 kV), it is possible from the conventional Td-Vd characteristics to identify the flashover discharge path length regardless of the experimental system and electrode configuration. On the other hand, at high voltages (Vd > 40 kV), Td is longer than the expected value based on the conventional Td-Vd characteristics, which may be affected not only by the propagation time of the conductive channel but also by the propagation time of secondary electron avalanche and the developing time of gap discharge.

    DOI: 10.23919/CMD54214.2022.9991358

    Scopus

    Other Link: https://www.webofscience.com/api/gateway?GWVersion=2&SrcApp=iroffice_5964&SrcAuth=WosAPI&KeyUT=WOS:000937794300092&DestLinkType=FullRecord&DestApp=WOS_CPL

  41. 異種材料対向電極の真空中コンディショニングにおける放電電荷量と対向電極材料付着の推移

    北直樹,小島寛樹,福田英昭,山村健太,早川直樹

    令和4年電気学会基礎・材料・共通部門大会  2022.9.13  電気学会基礎・材料・共通部門

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    Event date: 2022.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:西之表市民会館   Country:Japan  

  42. 真空中固体絶縁物上の沿面放電における放電進展時間の電圧依存性

    渡會凌平,小島寛樹,道念大樹,山口信一,早川直樹

    令和4年電気学会基礎・材料・共通部門大会  2022.9.13  電気学会基礎・材料・共通部門

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    Event date: 2022.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:西之表市民会館   Country:Japan  

  43. コンデンサ形計器用変圧器のPD測定へのTEVセンサの適用

    永木雄也,小島寛樹,吉田昌展,早川直樹

    令和4年電気学会電力・エネルギー部門大会  2022.9.8  電気学会電力・エネルギー部門

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    Event date: 2022.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:福井大学 文京キャンパス   Country:Japan  

  44. 多端子直流送電システムの超電導限流器配置に関する考察

    村上雅紀,小島寛樹,早川直樹

    令和四年度電気・電子・情報関係学会東海支部連合大会  2022.8.30  電気学会東海支部,電子情報通信学会東海支部,情報処理学会東海支部,照明学会東海支部,映像情報メディア学会東海支部,日本音響学会東海支部,IEEE名古屋支部

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    Event date: 2022.8

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  45. Temperature Rise on Permittivity and Conductivity Graded Materials (ε/σ-FGM) Spacer for HVDC GIS/GIL Invited

    Rachmawati, H. Kojima, N. Hayakawa

    2022.8.30 

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    Event date: 2022.8

    Language:English   Presentation type:Oral presentation (general)  

    Country:Japan  

  46. ε-FGMスペーサ沿面上に金属異物が付着した場合におけるSF6ガス中フラッシオーバ電圧

    加藤英明,加藤拓夢,小島寛樹,蒲原聖也,保科好一,早川直樹

    令和四年度電気・電子・情報関係学会東海支部連合大会  2022.8.30  電気学会東海支部,電子情報通信学会東海支部,情報処理学会東海支部,照明学会東海支部,映像情報メディア学会東海支部,日本音響学会東海支部,IEEE名古屋支部

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    Event date: 2022.8

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  47. 245kV級GIS用ε-FGMスペーサにおけるフラッシオーバ起点

    加藤拓夢,小島寛樹,加藤克巳,大久保仁,足立和郎,岡本健次,早川直樹

    令和四年度電気・電子・情報関係学会東海支部連合大会  2022.8.30  電気学会東海支部,電子情報通信学会東海支部,情報処理学会東海支部,照明学会東海支部,映像情報メディア学会東海支部,日本音響学会東海支部,IEEE名古屋支部

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    Event date: 2022.8

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  48. 陰極Cu-陽極SUS電極系の真空中コンディショニングによる絶縁耐圧向上効果

    北直樹,小島寛樹,福田英昭,山村健太,早川直樹

    令和四年度電気・電子・情報関係学会東海支部連合大会  2022.8.30  電気学会東海支部,電子情報通信学会東海支部,情報処理学会東海支部,照明学会東海支部,映像情報メディア学会東海支部,日本音響学会東海支部,IEEE名古屋支部

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    Event date: 2022.8

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  49. コンデンサ形計器用変圧器におけるアルミ箔/油浸紙複合絶縁系の部分放電進展特性

    林恭平,脇田周太,永木雄也,小島寛樹,吉田昌展,早川直樹

    令和四年度電気・電子・情報関係学会東海支部連合大会  2022.8.30  電気学会東海支部,電子情報通信学会東海支部,情報処理学会東海支部,照明学会東海支部,映像情報メディア学会東海支部,日本音響学会東海支部,IEEE名古屋支部

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    Event date: 2022.8

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  50. 真空中固体絶縁物上の沿面放電開始に及ぼす帯電分布形状の影響

    杉浦拓真,小島寛樹,早川直樹

    令和四年度電気・電子・情報関係学会東海支部連合大会  2022.8.29  電気学会東海支部,電子情報通信学会東海支部,情報処理学会東海支部,照明学会東海支部,映像情報メディア学会東海支部,日本音響学会東海支部,IEEE名古屋支部

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    Event date: 2022.8

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  51. モンテカルロ法による真空中絶縁破壊後の金属蒸気拡散の推定

    小名木良太,小島寛樹,飯塚伸介,小林将人,早川直樹

    令和四年度電気・電子・情報関係学会東海支部連合大会  2022.8.29  電気学会東海支部,電子情報通信学会東海支部,情報処理学会東海支部,照明学会東海支部,映像情報メディア学会東海支部,日本音響学会東海支部,IEEE名古屋支部

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    Event date: 2022.8

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  52. 電動推進航空機用モータにおける流動潤滑油の絶縁破壊特性

    鎌田泰任,小島寛樹,有賀信雄,卯辰清志,渡邉瞬也,早川直樹

    令和四年度電気・電子・情報関係学会東海支部連合大会  2022.8.30  電気学会東海支部,電子情報通信学会東海支部,情報処理学会東海支部,照明学会東海支部,映像情報メディア学会東海支部,日本音響学会東海支部,IEEE名古屋支部

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    Event date: 2022.8

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  53. 大規模再生可能エネルギー導入とGIS Invited

    小島寛樹

    電気学会電力・エネルギーフォーラム「ガス絶縁開閉装置に要求されるIT化融合技術と再生可能エネルギー対応技術の動向」  2022.6.29  電気学会電力・エネルギー部門開閉保護技術委員会

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    Event date: 2022.6

    Language:Japanese   Presentation type:Public lecture, seminar, tutorial, course, or other speech  

    Venue:電気学会   Country:Japan  

  54. Partial Discharge Progress and Breakdown Characteristics of Aluminum Foil/Oil-impregnated Paper Insulation System International conference

    N. Hayakawa, S. Wakita, Y. Nagaki, M. Yoshida, H. Kojima

    21st IEEE International Conference on Dielectric Liquids  2022.6.2  IEEE DEIS

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    Event date: 2022.5 - 2022.6

    Language:English   Presentation type:Poster presentation  

    Venue:Seville   Country:Spain  

    Static capacitors (SC) and capacitor voltage transformers (CVT) operated over 30 years in substations are composed of aluminum foil/oil-impregnated paper insulation system. For the condition monitoring and diagnosis of aged SCs and CVTs, partial discharge (PD) measurement is expected. However, PD characteristics from PD inception and progress to breakdown (BD) are not yet clarified. Thus, in this paper, we carried out electrical and optical investigation of PD progress and BD characteristics of a fundamental insulation model composed of aluminum foil/oil-impregnated paper insulation system. As a result, we clarified that PD progress can be classified into 3 periods. In the Period 1, PD signals less than 500 pC were intermittently generated around the peak phase of applied AC voltage and dot-like PD light emission was observed at the edge of aluminum foil. In the Period 2, PD signals larger than 500 pC were continuously generated around zero crossing (void discharge) to peak phase and PD light emission was observed on the peripheries of the aluminum foil. In the Period 3, PD signals larger than 10,000 pC were generated with the extended PD light emission and bubbles, leading to BD through the oil-impregnated papers.

    DOI: 10.1109/ICDL49583.2022.9830964

    Scopus

  55. Expected Lifetime Evaluation of Oil-impregnated Paper Capacitors International conference

    M. Yoshida, Y. Nagaki, H. Kojima, N. Hayakawa

    21st IEEE International Conference on Dielectric Liquids  2022.6.2  IEEE DEIS

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    Event date: 2022.5 - 2022.6

    Language:English   Presentation type:Poster presentation  

    Venue:Seville   Country:Spain  

    This paper describes the concept of a method for evaluating the insulation lifetime for oil-impregnated paper capacitors in capacitor voltage transformers (CVTs), based on the short-term breakdown characteristics and partial discharge inception characteristics of aged oil-impregnated paper capacitors. In addition, the time margin (lead time) from the inception of partial discharge to breakdown at the operating electric field of CVT is evaluated.

    DOI: 10.1109/ICDL49583.2022.9830938

    Scopus

  56. 多端子直流送電システムにおける超電導限流器の限流効果および過渡安定度向上効果

    村上雅紀,小島寛樹,早川直樹

    令和4年電気学会全国大会  2022.3.22  電気学会

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    Event date: 2022.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  57. 不平等電界下におけるCO2/N2混合ガス中絶縁破壊メカニズムの混合比依存性

    尾﨑脩平,小島寛樹,早川直樹

    令和4年電気学会全国大会  2022.3.23  電気学会

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    Event date: 2022.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  58. 電動推進航空機用モータの高出力密度化に向けた潤滑油中コイルモデルの部分放電開始特性

    鎌田泰任,脇田周太,小島寛樹,有賀信雄,卯辰清志,渡邉瞬也,早川直樹

    令和4年電気学会全国大会  2022.3.21  電気学会

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    Event date: 2022.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  59. 油浸紙コンデンサの期待寿命評価の検討

    永木雄也,小島寛樹,吉田昌展,早川直樹

    令和4年電気学会全国大会  2022.3.21  電気学会

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    Event date: 2022.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  60. アルミ箔/油浸紙複合絶縁系における絶縁破壊に至る部分放電特性の推移

    脇田周太,林恭平,永木雄也,小島寛樹,吉田昌展,早川直樹

    令和4年電気学会全国大会  2022.3.21  電気学会

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    Event date: 2022.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  61. 放電開始条件を考慮したFGM絶縁スペーサの誘電率分布逆求解計算

    加藤克巳,小島寛樹,早川直樹,増井秀好,柳瀬博雅,岡本健次,大久保仁

    令和4年電気学会全国大会  2022.3.23  電気学会

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    Event date: 2022.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  62. 実器サイズGIS用ε-FGMスペーサにおける絶縁破壊特性の理論的検討

    加藤拓夢,小島寛樹,加藤克巳,大久保仁,足立和郎,岡本健次,早川直樹

    令和4年電気学会全国大会  2022.3.23  電気学会

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    Event date: 2022.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  63. Discharge Inception Voltage Improvement by Application of Permittivity and Conductivity Graded Materials (ε/σ-FGM) to HVDC GIS Spacer

    Rachmawati, H. Kojima, K. Kato, N. Hayakawa

    The 2022 Annual Meeting of the Institute of Electrical Engineers of Japan  2022.3.23  Institute of Electrical Engineers of Japan

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    Event date: 2022.3

    Language:English   Presentation type:Oral presentation (general)  

    Venue:online   Country:Japan  

  64. 真空中コンディショニング飽和時の絶縁耐力に及ぼす放電電荷量と対向電極材料付着の影響

    北直樹,小島寛樹,福田英昭,山村健太,早川直樹

    令和4年電気学会全国大会  2022.3.21  電気学会

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    Event date: 2022.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  65. 真空中高周波交流コンディショニングにおける多重絶縁破壊に関する考察

    小名木良太,小島寛樹,飯塚伸介,小林将人,早川直樹

    令和4年電気学会全国大会  2022.3.21  電気学会

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    Event date: 2022.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  66. 異種材料が対向する電極の真空中コンディショニングにおける絶縁耐力と材料付着の放電電荷量依存性

    北直樹,小島寛樹,福田英昭,山村健太,早川直樹

    電気学会誘電・絶縁材料/放電・プラズマ・パルスパワー/高電圧合同研究会  2022.1.21  電気学会誘電・絶縁材料/放電・プラズマ・パルスパワー/高電圧技術委員会

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    Event date: 2022.1

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:北九州国際会議場   Country:Japan  

    CiNii Research

  67. CO2/N2混合ガス中におけるチャネル加熱絶縁破壊電圧

    尾﨑脩平,小島寛樹,早川直樹

    令和3年(2021年)放電学会年次大会  2021.12.3  放電学会

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    Event date: 2021.12

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  68. 真空中固体絶縁物上における帯電分布形状が沿面放電電圧に与える影響

    渡會凌平,小島寛樹,早川直樹

    令和3年(2021年)放電学会年次大会  2021.12.3  放電学会

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    Event date: 2021.12

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  69. Flashover Voltage Estimation of Cone-type GIS Spacer with Permittivity Graded Materials (ε-FGM) by Volume-Time Theory in Consideration with Conductor Surface Roughness in SF6 Gas Invited International conference

    N. Hayakawa, Y. Miyazaki, H. Kojima, K. Kato, H. Okubo, K. Adachi, K. Okamoto

    22nd International Symposium on High Voltage Engineering  2021.11.23  Xi'an Jiaotong University, State Key Laboratory of Electrical Insulation and Power Equipment, China Electrotechnical Society, Engineering Dielectrics Technical Committee, China Society for Electrical Engineering, Chinese National Committee of CIGRE, High Voltage Technical Committee and The International Council on Large Electric Systems

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    Event date: 2021.11

    Language:English   Presentation type:Oral presentation (invited, special)  

    Venue:Xi'an   Country:China  

    Toward the compact gas insulated switchgears (GIS) and transmission lines (GIL), we have been investigating a novel electric field grading technique around the GIS spacer by “functionally graded materials (FGM)” with spatial distribution of permittivity (ε-FGM). We have already designed and fabricated the cone-type ε-FGM spacer samples with the relative permittivity distribution between 10 and 4 for 245 kV class GIS and obtained the higher flashover voltage (FOV) than that of the spacer samples with uniform permittivity. In this paper, in order to verify the estimated FOV of the ε-FGM spacer samples, we estimated the theoretical discharge inception voltage (TDIV50) by the analytical approach with the extended Volume-Time theory in consideration with the conductor surface roughness. The estimated TDIV50 of the ε-FGM spacer sample was verified to be consistent with the measured FOV and higher by 28 % in SF6 gas at 0.6 MPa-abs than that of the conventional spacer sample.

    DOI: 10.1049/icp.2022.0260

    Scopus

  70. Inverse Analysis of Optimum Permittivity Distribution for FGM Spacer in Consideration with Multiple Objective Functions in Gaseous Insulation System International conference

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

    22nd International Symposium on High Voltage Engineering  2021.11.24  Xi'an Jiaotong University, State Key Laboratory of Electrical Insulation and Power Equipment, China Electrotechnical Society, Engineering Dielectrics Technical Committee, China Society for Electrical Engineering, Chinese National Committee of CIGRE, High Voltage Technical Committee and The International Council on Large Electric Systems

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    Event date: 2021.11

    Language:English   Presentation type:Poster presentation  

    Venue:Xi'an   Country:China  

    For relaxation of electric field (E-field) stress around solid insulation spacer in HV-GIS (Gas Insulated Switchgears), we have proved the effectiveness of an application of functionally graded materials (FGM) with spatial distribution of permittivity (ε-FGM). For this purpose, we have proposed a technique for inverse analysis of the permittivity distribution in an ε-FGM spacer. The technique can provide us optimum permittivity distribution with the maximum E-field stress relaxation with less computation time. In this paper, we developed the new technique of the inverse analysis under the consideration of multiple objective functions on the insulation performances. In our study, we focus on three kinds of functions: (a) dielectric strength in SF6 gas gap, (b) dielectric strength on the spacer surface, and (c) dielectric strength on the embedded electrode/epoxy spacer interface. Under the consideration of three objective functions, the optimum permittivity distribution in ε-FGM spacer are modified full-automatically. Through the application results to GIS spacer, we obtain the inverse analysis of optimum permittivity distribution by only 11 times of iterations. As a result, we obtained 25% improvement of insulation performance around ε-FGM spacer compared with the conventional spacer with uniform permittivity distribution.

    DOI: 10.1049/icp.2022.0245

    Scopus

  71. Time Transition of Gas Conductivity and Charge Behavior in SF6-Epoxy Composite Insulation System Under DC Partial Discharge International conference

    R. Nakane, H. Kojima, N. Hayakawa

    22nd International Symposium on High Voltage Engineering  2021.11.24  Xi'an Jiaotong University, State Key Laboratory of Electrical Insulation and Power Equipment, China Electrotechnical Society, Engineering Dielectrics Technical Committee, China Society for Electrical Engineering, Chinese National Committee of CIGRE, High Voltage Technical Committee and The International Council on Large Electric Systems

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    Event date: 2021.11

    Language:English   Presentation type:Poster presentation  

    Venue:Xi'an   Country:China  

    The charge accumulation at the interface between gas medium and solids in DC gas insulated switchgear (DC-GIS) and DC gas insulated line (DC-GIL) is crucial in their electrical insulation design and operation. In this paper, the charging process on solid insulator surface under DC partial discharge (DC-PD) in SF6 gas is reported. A needle-epoxy plane electrode system is installed in SF6 gas at atmospheric pressure. The measured surface potential distribution on epoxy plate is compared with the simulation considering charge behavior in SF6 gas such as ion generation due to DC-PD, drift and diffusion. As a result, we quantitatively clarify the charge accumulation process under DC-PD as the main source of charge carrier in terms of the activated conductivity distribution in SF6 gas. The charging process under DC-PD is attributed to the time transition of activated conductivity distribution in SF6 gas gap, which is approximately 1010 times higher than that in non-activated conductivity space. This means that the activated conductivity distribution in SF6 gas is the crucial parameter that determines the charging process for DC-GIS/GIL under DC-PD occurrence.

    DOI: 10.1049/icp.2022.0474

    Scopus

  72. Application of SiC-filled Permittivity and Conductivity Graded Material (ε/σ-FGM) in HVDC GIS Spacer International coauthorship International conference

    Rachmawati, H. Kojima, K. Kato, N. Zebouchi, N. Hayakawa

    22nd International Symposium on High Voltage Engineering  2021.11.24  Xi'an Jiaotong University, State Key Laboratory of Electrical Insulation and Power Equipment, China Electrotechnical Society, Engineering Dielectrics Technical Committee, China Society for Electrical Engineering, Chinese National Committee of CIGRE, High Voltage Technical Committee and The International Council on Large Electric Systems

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    Event date: 2021.11

    Language:English   Presentation type:Oral presentation (general)  

    Venue:Xi'an   Country:China  

    The size reduction of HVDC GIS is needed for reduction of SF6 gas use. The challenge concerning the insulating material in HVDC GIS is to reduce the high electric field strength in gas around the solid insulators (spacers). Our previous works have shown the effectiveness of the functionally graded material (FGM) with graded permittivity (ε) and conductivity (σ) in controlling the high electric field strength under various DC operating conditions. However, ε/σ distributions were independent of each other. For practical implementation of FGM to HVDC GIS, the flexible mixture casting (FMC) method so far allows us to create a material whose ε/σ distributions are interdependent. In this paper, based on the measured dependence between ε and σ in SiC-filled epoxy composites, the electric field relaxation effect is evaluated under three different ε/σ distributions (U-type, grading-to-higher conductivity (GHC)-type and grading-to-lower conductivity (GLC)-type) applied to a 320 kV HVDC GIS spacer model. The results show that GLC-type ε/σ-FGM has effectively and constantly reduced the maximum electric field strength under the time-varying voltage application from DC-on to DC-steady state and against temperature differences between the high voltage and ground sides up to 70 K.

    DOI: 10.1049/icp.2022.0264

    Scopus

  73. Discrimination of Discharge Pattern in Cut Model of Vacuum Interrupter International conference

    H. Kojima, T. Donen, T. Kimura, K. Kokura, N. Hayakawa

    29th International Symposium on Discharges and Electrical Insulation in Vacuum  2021.9.28  Consorzio RFX

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    Event date: 2021.9

    Language:English   Presentation type:Oral presentation (general)  

    Venue:Padova   Country:Italy  

    Electrical insulation of a vacuum interrupter (VI) is a composite system composed of vacuum, metal, and solid insulator. Detection of weak points in insulation is important for insulation design of VI. However, solid insulators of VI are mostly made of opaque ceramics, and it is very difficult to directly visually observe discharge sites and patterns inside VI. Previously, we have proposed a discrimination method of discharge patterns in VI by extracting features of applied voltage, discharge current, and shield potential change. In this study, we aim to verify that our proposing method can be applied to an actual structure of VI. We prepared a cut model of VI, whose shield electrode and alumina ceramic insulators have been partly cut for observing the discharge site. In this VI cut model, we simulated the weak points in insulation by additional needle electrodes. We applied a negative standard lightning impulse voltage between contact electrodes, and measured the applied voltage, the shield potential, and the anode current. In various settings, we almost succeeded to discriminate the initiation pattern of discharge, even in the case of complex discharge pattern with gap and/or surface discharge. In this verification, we found the new discharge pattern, in which the first gap discharge induced another gap discharge due to the diffusion of particles from the first discharge. However, by modifying the discrimination method based on the above physical mechanism of new discharge pattern, we got the prospects that the method can be applied to actual VI structure.

    DOI: 10.1109/ISDEIV46977.2021.9586961

    Scopus

  74. Anode Material Adhesion to Cathode during Spark Conditioning Process in Vacuum International conference

    N. Kita, H. Kojima, H. Fukuda, M. Sakaki, N. Hayakawa

    29th International Symposium on Discharges and Electrical Insulation in Vacuum  2021.9.27  Consorzio RFX

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    Event date: 2021.9

    Language:English   Presentation type:Poster presentation  

    Venue:Padova   Country:Italy  

    Spark conditioning is an effective method to improve electrical insulation strength of vacuum circuit breakers. In the conditioning process, defects on cathode surface are removed by repetitive breakdowns (BDs). However, we have elucidated that at the same time, micro-protrusions can be generated on the cathode surface by the adhesion of melted particles of anode material. In this paper, we discuss the relationship between the anode material adhesion to cathode and the conditioning saturation from an experimental approach. We set rod-plane electrodes made of Cu and stainless steel (SUS) in a vacuum chamber. We conduct spark conditioning by repetitive impulse voltages for several pairs of Cu and SUS electrodes. To one pair, the voltage is applied until the conditioning saturation. To the others, the smaller number of voltages before conditioning saturation is applied. After that, we observe the surface of rod cathodes with a digital microscope. As a result, we observe protrusion-like adhesion of the anode material to the cathode surface after conditioning saturation. On the other hand, we confirm coat-like adhesion of the anode material to the cathode surface before conditioning saturation. From these results, it is considered that coat-like adhesion mainly occur up to the saturation voltage, and then protrusion-like adhesion occur due to BD at the saturation voltage level. In other words, the generation of micro-protrusions can be a dominant factor of conditioning saturation process in vacuum.

    DOI: 10.1109/ISDEIV46977.2021.9586907

    Scopus

  75. Dielectric Strength Improvement by Higher Frequency AC Conditioning International conference

    R. Konagi, H. Kojima, S. Iitsuka, M. Kobayashi, N. Hayakawa

    29th International Symposium on Discharges and Electrical Insulation in Vacuum  2021.9.28  Consorzio RFX

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    Event date: 2021.9

    Language:English   Presentation type:Oral presentation (general)  

    Venue:Padova   Country:Italy  

    We discuss the effects of AC conditioning with higher frequency on the dielectric strength in vacuum. We have confirmed that multiple breakdowns occur in a half cycle of AC voltage application in the AC conditioning process. It is considered that the multiple breakdowns are triggered by metal vapor due to the previous breakdown in the same half cycle. Such breakdowns can not be attributed to a micro protrusion on the electrode surface. Therefore, multiple breakdowns are considered not effective, but harmful for conditioning. In this paper, we carried out the AC conditioning with the higher frequency than the commercial power frequency in the sphere-plane electrode system. We experimentally confirmed that the conditioning effect is improved by increasing the frequency of AC conditioning in the sphere-plane electrode system, where multiple or harmful breakdowns were suppressed during AC conditioning. These results suggest the feasibility of higher frequency AC conditioning for the dielectric strength improvement in vacuum.

    DOI: 10.1109/ISDEIV46977.2021.9586929

    Scopus

  76. アルミ箔/油浸紙複合絶縁系における部分放電開始・進展・絶縁破壊特性

    脇田周太,永木雄也,小島寛樹,吉田昌展,早川直樹

    第52回電気電子絶縁材料システムシンポジウム  2021.9.14  電気学会誘電・絶縁材料技術委員会

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    Event date: 2021.9

    Language:Japanese   Presentation type:Poster presentation  

    Venue:オンライン   Country:Japan  

  77. Theoretical Investigation on Discharge Inception Voltage Improvement of SiC-filled Permittivity and Conductivity Graded Material (ε/σ-FGM) for HVDC GIS International coauthorship

    Rachmawati, H. Kojima, K. Kato, N. Zebouchi, N. Hayakawa

    52nd Symposium on Electrical and Electronic Insulating Materials and Applications in Systems  2021.9.14  IEEJ Technical Committee on Dielectrics and Electrical Insulation

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    Event date: 2021.9

    Language:English   Presentation type:Poster presentation  

    Venue:WEB   Country:Japan  

  78. 電動推進航空機用モータにおける潤滑油絶縁の適用可能性

    鎌田泰任,脇田周太,小島寛樹,有賀信雄,卯辰清志,渡邉瞬也,早川直樹

    第52回電気電子絶縁材料システムシンポジウム  2021.9.14  電気学会誘電・絶縁材料技術委員会

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    Event date: 2021.9

    Language:Japanese   Presentation type:Poster presentation  

    Venue:オンライン   Country:Japan  

  79. X線CTを用いた誘電率傾斜機能材料(ε-FGM)の誘電率分布測定

    加藤拓夢,小島寛樹,柳瀬博雅,岡本健次,早川直樹

    令和三年度電気・電子・情報関係学会東海支部連合大会  2021.9.8  電気学会東海支部,電子情報通信学会東海支部,情報処理学会東海支部,照明学会東海支部,映像情報メディア学会東海支部,日本音響学会東海支部,IEEE名古屋支部

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    Event date: 2021.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:愛知工業大学(オンライン開催)   Country:Japan  

  80. アルミ箔/油浸紙複合絶縁系における部分放電発光の電圧依存性

    脇田周太,永木雄也,小島寛樹,吉田昌展,早川直樹

    令和三年度電気・電子・情報関係学会東海支部連合大会  2021.9.7  電気学会東海支部,電子情報通信学会東海支部,情報処理学会東海支部,照明学会東海支部,映像情報メディア学会東海支部,日本音響学会東海支部,IEEE名古屋支部

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    Event date: 2021.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:愛知工業大学(オンライン開催)   Country:Japan  

  81. 電動推進航空機用モータに向けた潤滑油の絶縁破壊基礎特性

    鎌田泰任,脇田周太,小島寛樹,有賀信雄,卯辰清志,渡邉瞬也,早川直樹

    令和三年度電気・電子・情報関係学会東海支部連合大会  2021.9.7  電気学会東海支部,電子情報通信学会東海支部,情報処理学会東海支部,照明学会東海支部,映像情報メディア学会東海支部,日本音響学会東海支部,IEEE名古屋支部

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    Event date: 2021.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:愛知工業大学(オンライン開催)   Country:Japan  

  82. CO2/N2混合ガス中におけるチャネル加熱絶縁破壊発生電圧

    尾﨑脩平,小島寛樹,早川直樹

    令和三年度電気・電子・情報関係学会東海支部連合大会  2021.9.7  電気学会東海支部,電子情報通信学会東海支部,情報処理学会東海支部,照明学会東海支部,映像情報メディア学会東海支部,日本音響学会東海支部,IEEE名古屋支部

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    Event date: 2021.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:愛知工業大学(オンライン開催)   Country:Japan  

  83. 真空中固体絶縁物上における帯電分布形状が沿面放電電圧に与える影響

    渡會凌平,小島寛樹,早川直樹

    令和三年度電気・電子・情報関係学会東海支部連合大会  2021.9.7  電気学会東海支部,電子情報通信学会東海支部,情報処理学会東海支部,照明学会東海支部,映像情報メディア学会東海支部,日本音響学会東海支部,IEEE名古屋支部

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    Event date: 2021.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:愛知工業大学(オンライン開催)   Country:Japan  

  84. Discharge Inception Voltage Calculation of HVDC GIS with Graded Permittivity and Conductivity (ε/σ-FGM) Spacer

    Rachmawati, H. Kojima, K. Kato, N. Hayakawa

    2021 Tokai-Section Joint Conference on Electrical, Electronics, Information, and Related Engineering  2021.9.8 

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    Event date: 2021.9

    Language:English   Presentation type:Oral presentation (general)  

    Venue:Aichi Institute of Technology (Online)   Country:Japan  

  85. 真空中高周波交流コンディショニングにおける放電の電子温度

    小名木良太,小島寛樹,飯塚伸介,小林将人,早川直樹

    令和三年度電気・電子・情報関係学会東海支部連合大会  2021.9.7  電気学会東海支部,電子情報通信学会東海支部,情報処理学会東海支部,照明学会東海支部,映像情報メディア学会東海支部,日本音響学会東海支部,IEEE名古屋支部

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    Event date: 2021.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:愛知工業大学(オンライン開催)   Country:Japan  

  86. 真空中におけるコンディショニングと放電電荷量の相関

    北直樹,小島寛樹,福田英昭,榊正幸,早川直樹

    令和三年度電気・電子・情報関係学会東海支部連合大会  2021.9.7  電気学会東海支部,電子情報通信学会東海支部,情報処理学会東海支部,照明学会東海支部,映像情報メディア学会東海支部,日本音響学会東海支部,IEEE名古屋支部

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    Event date: 2021.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:愛知工業大学(オンライン開催)   Country:Japan  

  87. 真空中高周波交流コンディショニングによる耐圧向上効果 ~放電発光スペクトルからみた考察~

    小名木良太,小島寛樹,飯塚伸介,小林将人,早川直樹

    令和3年電気学会基礎・材料・共通部門大会  2021.9.3  電気学会基礎・材料・共通部門

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    Event date: 2021.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  88. 誘電率傾斜機能材料(ε-FGM)における誘電率分布の非破壊測定

    加藤拓夢,小島寛樹,柳瀬博雅,岡本健次,早川直樹

    令和3年電気学会基礎・材料・共通部門大会  2021.9.3  電気学会基礎・材料・共通部門

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    Event date: 2021.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  89. 真空中におけるコンディショニング過程で生成する微小突起サイズ

    北直樹,小島寛樹,福田英昭,榊正幸,早川直樹

    令和3年電気学会電力・エネルギー部門大会  2021.8.26  電気学会電力・エネルギー部門

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    Event date: 2021.8

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  90. 繰り返しサージ電圧下のエナメル線の部分放電開始電圧における湿度および気圧依存性

    林亮平,小島寛樹,早川直樹

    令和3年電気学会全国大会  2021.3.11  電気学会

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    Event date: 2021.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  91. 真空中コンディショニングの飽和過程における対向電極材料の付着

    北直樹,小島寛樹,福田英昭,榊正幸,早川直樹

    令和3年電気学会全国大会  2021.3.10  電気学会

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    Event date: 2021.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  92. 真空中高周波交流コンディショニングにおける多重絶縁破壊の抑制による耐圧向上効果

    小名木良太,小島寛樹,飯塚伸介,小林将人,早川直樹

    令和3年電気学会全国大会  2021.3.10  電気学会

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    Event date: 2021.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  93. Electric Field Grading on HVDC GIS Spacer by SiC-filled Permittivity and Conductivity Graded Material (ε/σ-FGM)

    Rachmawati, H. Kojima, K. Kato, N. Hayakawa

    The 2021 Annual Meeting of the Institute of Electrical Engineers of Japan  2021.3.11  IEEJ

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    Event date: 2021.3

    Language:English   Presentation type:Oral presentation (general)  

    Venue:online   Country:Japan  

  94. SF6ガス中FGM絶縁スペーサの最適絶縁性能を目指した誘電率分布逆求解技術

    加藤克巳,小島寛樹,早川直樹,増井秀好,柳瀬博雅,岡本健次,大久保仁

    令和3年電気学会全国大会  2021.3.11  電気学会

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    Event date: 2021.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  95. 超電導パンケーキコイルの対地絶縁モデルにおける液体窒素の動的絶縁破壊特性

    森優次,村上雅紀,小島寛樹,早川直樹

    令和3年電気学会全国大会  2021.3.11  電気学会

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    Event date: 2021.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  96. アルミ箔/油浸紙複合絶縁系における部分放電および絶縁破壊特性

    脇田周太,小島寛樹,吉田昌展,早川直樹

    令和3年電気学会全国大会  2021.3.9 

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    Event date: 2021.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  97. SF6ガス/エポキシ複合絶縁系の直流部分放電下におけるガス中導電率分布の時間推移

    中根龍一,小島寛樹,早川直樹

    令和3年電気学会全国大会  2021.3.11 

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    Event date: 2021.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  98. Diagnosis of Discharge Pattern in Vacuum Interrupter by Shield Potential Measurement International conference

    H. Kojima, T. Donen, T. Kimura, N. Hayakawa

    8th International Conference on Condition Monitoring and Diagnosis  2020.10.28  Department of Electrical Engineering, Faculty of Engineering, King Mongkut's Institute of Technology Ladkrabang

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    Event date: 2020.10

    Language:English   Presentation type:Oral presentation (general)  

    Venue:King Mongkut's Institute of Technology Ladkrabang   Country:Thailand  

    In vacuum discharge, we found that the discharge developing time depends only upon the discharge path length in the case of gap discharge, whereas it is in inverse proportion to the square of the discharge inception voltage in the case of surface flashover. Based on the database for fundamental electrode configuration, we have proposed a diagnosing method of discharge pattern in vacuum interrupter (VI). In this paper, we applied the diagnosing method to an actual VI model and verified the effectiveness of the method. We measured the applied voltage and the shield potential with voltage dividers and the discharge current with high-frequency current transformer. We also captured the still image of discharge by a digital camera to verify the discharge path in the VI model with an observation aperture. By changing the electrode configuration in the VI model, we observed the various discharge patterns, e.g. the gap discharge between contacts, the surface flashover on the solid insulator through the shield, and the combination of them. Experimental results revealed that we succeeded in diagnosing the discharge pattern with the validity higher than 90%.

    DOI: 10.1109/CMD48350.2020.9287205

    Scopus

    Other Link: https://www.webofscience.com/wos/woscc/full-record/WOS:000941411400043

  99. Pressure Dependence of Quench-induced Dynamic Breakdown Characteristics of HTS Pancake Coil Model for Resistive SFCL International conference

    N. Hayakawa, Y. Mori, H. Kojima

    Applied Superconductivity Conference 2020  2020.11.4 

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    Event date: 2020.10 - 2020.11

    Language:English   Presentation type:Oral presentation (general)  

    Venue:virtual conference   Country:United States  

  100. Dielectric Characteristics of Liquid Nitrogen / Synthetic Paper Composite Insulation System for Extra High Voltage HTS Cable International conference

    N. Hayakawa, K. Yamakami, T. Masuda, H. Kojima

    Applied Superconductivity Conference 2020  2020.11.3 

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    Event date: 2020.10 - 2020.11

    Language:English   Presentation type:Poster presentation  

    Venue:virtual conference   Country:United States  

  101. Time Transition of Conductivity Distribution in Air by DC Partial Discharge for Air-solid Composite Insulation Systems International conference

    R. Nakane, H. Kojima, J. Suehiro, H. Okubo, N. Hayakawa

    IEEE Conference on Electrical Insulation and Dielectric Phenomena 2020  2020.10.20  IEEE DEIS

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    Event date: 2020.10

    Language:English   Presentation type:Poster presentation  

    Venue:virtual conference   Country:United States  

    Toward the development of HVDC power apparatus, we investigate the charging process on solid insulator in terms of the time transition of conductivity distribution in air for air-solid composite insulation system from DC-on to DC steady-state. By using needle-air-PMMA-plane electrode configuration, we measure the time evolution of surface potential on PMMA due to partial discharge at the needle tip under negative DC voltage. We compare the measured surface potential distribution with the simulation result considering the charge behavior in air. Especially, a novel simulation model considering the charge supply due to DC partial discharge is built. As a result, in air-solid composite insulation system under negative DC application, the time transition of conductivity distribution in air corresponding to the charge accumulation is evaluated quantitatively.

    DOI: 10.1109/CEIDP49254.2020.9437492

    Scopus

  102. 電力機器内部アーク発生時の高温ガスによる周囲への熱的影響解析

    神足将司,岩田幹正,田所兼,田中慎一,小島寛樹,早川直樹

    電気学会放電・プラズマ・パルスパワー/静止器/開閉保護合同研究会  2020.9.28  電気学会放電・プラズマ・パルスパワー/静止器/開閉保護技術委員会

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    Event date: 2020.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

    CiNii Research

  103. Breakdown Characteristics of Cone-type ε-FGM Spacer for Gas Insulated Switchgears International conference

    Y. Miyazaki, A. Izu, Z. Liang, H. Kojima, H. Masui, H. Mitsudome, H. Yanase, K. Okamoto, K. Watanabe, K. Kato, N. Hayakawa

    9th International Symposium on Electrical Insulating Materials  2020.9.14  IEEJ Technical Committee on Dielectrics and Electrical Insulation

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    Event date: 2020.9

    Language:English  

    Venue:virtual web conference   Country:Japan  

    For the downsizing of gas insulated switchgears (GIS), a novel electric field grading technique is highly expected. In order to meet this demand, we have been investigating the electric field control and relaxation technique by "functionally graded materials" with the spatial distribution of permittivity (e-FGM). In this paper, we fabricated the 1/4-sized cone-type e-FGM spacer for 245 kV-class GIS and verified its breakdown voltage improvement effect by both experiment and simulation.

    Scopus

    Other Link: https://www.webofscience.com/wos/woscc/full-record/WOS:000789406400130

  104. Conductivity Distribution in Air by Charging Process on Solid Dielectrics under DC Voltage International conference

    R. Nakane, H. Kojima, N. Hayakawa, H. Okubo

    9th International Symposium on Electrical Insulating Materials  2020.9.14  IEEJ Technical Committee on Dielectrics and Electrical Insulation

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    Event date: 2020.9

    Language:English  

    Venue:virtual web conference   Country:Japan  

    The enhancement of DC electrical insulation performance is required for the reliable HVDC power equipment and bulk power transmission in recent years. In this paper, we measure the charging process on PMMA in air under DC steady-state and investigate the space distribution of the conductivity in air by using needle-air-PMMA-plane electrode configuration. In order to sfmulate the space distribution of the conductivity in air under DC steady-state, the charge transport equations in air considering the generation, recombination and motion of positive and negative ions are solved. We calculate the space distribution of the conductivity in air activated by partial discharge. As a result, it is quantitatively estimated that highly conductive area in air with approximately 106 times higher conductivity than the other area is formed along the electric line of force from the needle electrode tip as the source of charge carrier.

    Scopus

  105. Carbonization Phenomena Dependence on Pressure between Insulation Sheets by Steeper Inverter Surge at Inverter Fed Motor International conference

    Y. Yoshitake, H. Kojima, Y. Kasai, S. Maruyama, H. Kojima, N, Hayakawa

    9th International Symposium on Electrical Insulating Materials  2020.9.14  IEEJ Technical Committee on Dielectrics and Electrical Insulation

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    Event date: 2020.9

    Language:English  

    Venue:virtual web conference   Country:Japan  

    Recently, "carbonization phenomena on the insulation sheets" were newly detected as the unique precursor phenomena to the burning of the insulation of inverter-fed motors due to leakage current through the insulation system. We have previously studied the generation condition for the high dV/dt resulting in an inverter surge. In this study, we built an experimental setup based on an elemental model to simulate a steep surge voltages in the inverter and constructed the stator insulation inside the motor core to control the pressure between the insulation sheets. This paper reports the carbonization characteristics and the insulation design to prevent the carbonization caused by steep inverter surges.

    Scopus

  106. Electric Field Grading by Permittivity and Conductivity Graded Materials (ε/σ-FGM) for HVDC Gas Insulated Power Apparatus International coauthorship International conference

    Rachmawati, A. Izu, R. Nakane, H. Kojima, K. Kato, N. Zebouchi, N. Hayakawa

    9th International Symposium on Electrical Insulating Materials  2020.9.14  IEEJ Technical Committee on Dielectrics and Electrical Insulation

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    Event date: 2020.9

    Language:English  

    Venue:virtual web conference   Country:Japan  

    The progressive development of HVDC transmission system has urged us to develop a novel technique in supporting the performance of DC power apparatus. Functionally Graded Materials (FGM) are one of the techniques that allows us to control the electric field within the DC insulation system. Our previous work has reported that FGM with spatial conductivity distribution applied to a 320 kV DC-GIS spacer could reduce the maximum electric field under DC steady state condition. This paper investigates the applicability of the combination of spatial permittivity and conductivity graded materials (e/s-FGM) in DC power apparatus. ? / S - F G M are revealed to be more effective in suppressing maximum electric field as well as more uniformly distributed electric field against the increase of temperature distribution under polarity reversal, DC-on, and impulse superimposed on DC condition.

    Scopus

    Other Link: https://www.webofscience.com/wos/woscc/full-record/WOS:000789406400101

  107. 真空中コンディショニング過程で生成される微小突起サイズ

    北直樹,近藤史規,小島寛樹,福田英昭,榊正幸,早川直樹

    令和2年電気学会電力・エネルギー部門大会  2020.9.11 

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    Event date: 2020.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  108. 超電導限流器の動的絶縁破壊特性における体積効果

    森優次,小島寛樹,早川直樹

    令和2年電気学会電力・エネルギー部門大会  2020.9.11 

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    Event date: 2020.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  109. 実機サイズGISスペーサへのε-FGM(誘電率傾斜機能材料)の適用

    宮崎勇作,小島寛樹,早川直樹,加藤克巳,匹田政幸,大久保仁,渡辺桂司,岡本健次,足立和郎

    令和2年電気学会電力・エネルギー部門大会  2020.9.10 

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    Event date: 2020.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  110. ツイストペアの誘電損失によるエナメル皮膜温度上昇

    林亮平,梶武文,小島寛樹,早川直樹

    令和2年度電気・電子・情報関係学会東海支部連合大会 

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    Event date: 2020.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  111. Electric Field Grading by Permittivity and Conductivity Graded Material (ε/σ-FGM) at Polarity Reversal for HVDC GIS

    Rachmawati, H. Kojima, K. Kato, N. Hayakawa

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    Event date: 2020.9

    Language:English   Presentation type:Oral presentation (general)  

    Country:Japan  

  112. 超電導パンケーキコイルモデルにおける液体窒素の動的絶縁破壊電界の体積効果および熱流束依存性

    森優次,小島寛樹,早川直樹

    令和2年度電気・電子・情報関係学会東海支部連合大会 

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    Event date: 2020.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  113. 導電率傾斜機能材料(σ-FGM)のコーン型GISスペーサへの適用効果

    梁照源,宮崎勇作,小島寛樹,加藤克巳,増井秀好,満留博,柳瀬博雅,岡本健次,早川直樹

    令和2年度電気・電子・情報関係学会東海支部連合大会 

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    Event date: 2020.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  114. 可変配合注型法によるε-FGM(誘電率傾斜機能材料)を適用した実器サイズGISスペーサの誘電率分布測定

    宮崎勇作,小島寛樹,早川直樹,今井隆浩,染谷竜太,保科好一

    令和2年度電気・電子・情報関係学会東海支部連合大会 

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    Event date: 2020.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  115. 油浸紙絶縁における部分放電検出センサの感度比較

    脇田周太,小島寛樹,吉田昌展,早川直樹

    令和2年度電気・電子・情報関係学会東海支部連合大会 

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    Event date: 2020.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  116. 真空中高周波交流コンディショニングによる耐圧向上効果

    小名木良太,小島寛樹,飯塚伸介,小林将人,早川直樹

    令和2年度電気・電子・情報関係学会東海支部連合大会 

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    Event date: 2020.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  117. 真空中コンディショニング過程における陰極への陽極材料の付着が飽和電圧に与える影響

    北直樹,小島寛樹,福田英昭,榊正幸,早川直樹

    令和2年度電気・電子・情報関係学会東海支部連合大会 

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    Event date: 2020.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  118. 直流部分放電下の空気/固体複合絶縁系における空気中導電率分布の推移過程

    中根龍一,小島寛樹,大久保仁,早川直樹

    令和2年度電気・電子・情報関係学会東海支部連合大会 

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    Event date: 2020.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  119. 誘電率傾斜機能材料(ε-FGM)を用いたGISスペーサモデルの作製とSF6ガス中絶縁破壊電圧の理論的推定 Invited

    宮路仁崇,小島寛樹,加藤克巳,早川直樹

    令和2年電気学会基礎・材料・共通部門大会 

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    Event date: 2020.9

    Language:Japanese   Presentation type:Oral presentation (invited, special)  

    Venue:オンライン   Country:Japan  

  120. 空気/固体複合絶縁系の直流印加時における空気中導電率の時間推移

    中根龍一,小島寛樹,大久保仁,早川直樹

    令和2年電気学会基礎・材料・共通部門大会 

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    Event date: 2020.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  121. 真空中沿面放電における初期帯電迂回条件

    西田歩成,小名木良太,小島寛樹,飯塚伸介,小林将人,早川直樹

    令和2年電気学会全国大会 

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    Event date: 2020.3

    Language:Japanese  

    Venue:東京電機大学 東京千住キャンパス   Country:Japan  

  122. 真空中コンディショニング過程における対向電極材料の付着

    北直樹,近藤史規,小島寛樹,福田英昭,榊正幸,早川直樹

    令和2年電気学会全国大会 

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    Event date: 2020.3

    Language:Japanese  

    Venue:東京電機大学 東京千住キャンパス   Country:Japan  

  123. 真空中コンディショニングにおける陽極めっきの損耗

    近藤史規,北直樹,小島寛樹,鈴木飛鳥,小橋眞,福田英昭,榊正幸,早川直樹

    令和2年電気学会全国大会 

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    Event date: 2020.3

    Language:Japanese  

    Venue:東京電機大学 東京千住キャンパス   Country:Japan  

  124. ガス絶縁開閉装置向けコーン型ε-FGM(誘電率傾斜機能材料)スペーサの絶縁破壊特性

    宮崎勇作,伊豆淳宏,梁照源,小島寛樹,満留博,柳瀬博雅,岡本健次,渡辺桂司,加藤克巳,早川直樹

    令和2年電気学会全国大会 

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    Event date: 2020.3

    Language:Japanese  

    Venue:東京電機大学 東京千住キャンパス   Country:Japan  

  125. 導電率の温度・電界依存性を考慮した傾斜機能材料の直流ガス絶縁電力機器への適用効果

    伊豆淳宏,Rachmawati,中根龍一,小島寛樹,加藤克巳,早川直樹

    令和2年電気学会全国大会 

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    Event date: 2020.3

    Language:Japanese  

    Venue:東京電機大学 東京千住キャンパス   Country:Japan  

  126. 超高圧超電導ケーブルに向けた低誘電損失合成紙の電気絶縁特性

    山上浩輝,脇田周太,小島寛樹,増田孝人,早川直樹

    令和2年電気学会全国大会 

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    Event date: 2020.3

    Language:Japanese  

    Venue:東京電機大学 東京千住キャンパス   Country:Japan  

  127. 超電導パンケーキコイルモデルにおける液体窒素の動的絶縁破壊特性の圧力依存性

    森優次,山上浩輝,小島寛樹,早川直樹

    令和2年電気学会全国大会 

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    Event date: 2020.3

    Language:Japanese  

    Venue:東京電機大学 東京千住キャンパス   Country:Japan  

  128. 可変配合注型法による誘電率傾斜絶縁スペーサの樹脂分布可視化

    染谷竜太,保科好一,今井隆浩,小島寛樹,早川直樹

    令和2年電気学会全国大会 

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    Event date: 2020.3

    Language:Japanese  

    Venue:東京電機大学 東京千住キャンパス   Country:Japan  

  129. ツイストペアサンプルの部分放電開始電圧におけるエナメル皮膜の温度上昇

    林亮平,梶武文,小島寛樹,早川直樹

    令和2年電気学会全国大会 

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    Event date: 2020.3

    Language:Japanese  

    Venue:東京電機大学 東京千住キャンパス   Country:Japan  

  130. 空気中チャネル加熱絶縁破壊における電流増加および高導電率領域進展過程

    浅野竜大,小島寛樹,早川直樹

    令和2年電気学会全国大会 

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    Event date: 2020.3

    Language:Japanese  

    Venue:東京電機大学 東京千住キャンパス   Country:Japan  

  131. 空気/固体複合絶縁系の直流定常状態における空気中導電率の空間分布

    中根龍一,小島寛樹,早川直樹,大久保仁

    令和2年電気学会全国大会 

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    Event date: 2020.3

    Language:Japanese  

    Venue:東京電機大学 東京千住キャンパス   Country:Japan  

  132. 真空中交流部分放電による帯電形成時における固体絶縁物上の二次電子放出係数の時間推移

    大木駿士朗,小島寛樹,竪山智博,浅利直紀,佐々木良輔,早川直樹

    令和2年電気学会全国大会 

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    Event date: 2020.3

    Language:Japanese  

    Venue:東京電機大学 東京千住キャンパス   Country:Japan  

  133. 空気中チャネル加熱絶縁破壊における温度・電流上昇過程

    浅野竜大,小島寛樹,早川直樹

    電気学会誘電・絶縁材料/放電・プラズマ・パルスパワー/高電圧合同研究会  2020.1.24  電気学会誘電・絶縁材料/放電・プラズマ・パルスパワー/高電圧技術委員会

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    Event date: 2020.1

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:三菱電機健康保険組合 湯布郷館   Country:Japan  

    CiNii Research

  134. 超高圧超電導ケーブルに向けた液体窒素/合成紙複合絶縁系における部分放電開始特性

    山上浩輝,小島寛樹,増田孝人,早川直樹

    電気学会誘電・絶縁材料/放電・プラズマ・パルスパワー/高電圧合同研究会  2020.1.25  電気学会誘電・絶縁材料/放電・プラズマ・パルスパワー/高電圧技術委員会

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    Event date: 2020.1

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:三菱電機健康保険組合 湯布郷館   Country:Japan  

    CiNii Research

  135. 真空インタラプタ開口モデルによる複合的な放電経路に対する診断手法の検証

    小島寛樹,道念大樹,木村俊則,小倉健太郎,早川直樹

    電気学会放電・プラズマ・パルスパワー/開閉保護/高電圧合同研究会  2019.12.6  電気学会放電・プラズマ・パルスパワー/開閉保護/高電圧技術委員会

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    Event date: 2019.12

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:伊勢市観光文化会館(シンフォニアテクノロジー響ホール伊勢)   Country:Japan  

    CiNii Research

  136. Analysis of the Characteristics of Pressure Rise and Exhausted Hot Gas due to Internal Arc Faults in SF6-Insulated Power Equipment International conference

    M. Kotari, T. Tadokoro, S. Tanaka, M. Iwata, H. Kojima, N. Hayakawa

    2019 5th International Conference on Electric Power Equipment - Switching Technology  2019.10.15  Nagoya University

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    Event date: 2019.10

    Language:English   Presentation type:Oral presentation (general)  

    Venue:Kitakyushu   Country:Japan  

    From an environmental perspective, when performing internal arc tests on SF6-insulated power equipment, SF6 may be replaced with air in accordance with the International Electrotechnical Commission standard. To develop an alternative method for internal arc testing in SF6-insulated power equipment, a specific procedure must be proposed to replace SF6 with air and select appropriate test parameters. Therefore, we have systematically obtained the experimental and analytical data of air and SF6 arcs to calculate the pressure rise in electric power equipment and the thermal effect of hot gas on the surroundings. The modeling of SF6-air and air-air flows is implemented using computational fluid dynamics to analyze the characteristics of pressure rise and exhausted hot gas due to internal arc faults in SF6-insulated power equipment.

    DOI: 10.1109/ICEPE-ST.2019.8928689

    Scopus

  137. Suppression of Conditioning Effect in Vacuum by Micro-protrusions from Anode International conference

    F. Kondo, H. Kojima, H. Fukuda, M. Sakaki, N. Hayakawa

    2019 5th International Conference on Electric Power Equipment - Switching Technology  2019.10.14  Nagoya University

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    Event date: 2019.10

    Language:English   Presentation type:Oral presentation (general)  

    Venue:Kitakyushu   Country:Japan  

    Spark conditioning is an effective method to improve electrical insulation strength of vacuum circuit breakers. We discuss the spark conditioning process in consideration of the generation of micro-protrusions on cathode surface by breakdown. We conducted the spark conditioning on three pairs of rod-plane electrodes made of OFHC Cu. For one pair, the voltages were applied until conditioning saturation, namely 600 times voltage applications. For the others, a smaller number of voltage applications (100 times and 300 times) before conditioning saturation were given. After these conditioning experiments, we observed the surface of rod cathodes with a microscope. After the conditioning by about 600 times voltage applications, many micro-protrusions appeared on the cathode surface. Some of them had a diameter larger than 20 m. They would be caused by adhesion of metallic particles from anode and remained through the conditioning process. On the other hand, few micro-protrusions were found on the cathodes with 100 and 300 times voltage applications. This means that the micro-protrusions were generated at the last period of the conditioning process. In other words, the generation of micro-protrusions can be a dominant factor of suppression and saturation of conditioning effect.

    DOI: 10.1109/ICEPE-ST.2019.8928772

    Scopus

  138. 誘電率/導電率傾斜機能材料を用いた直流ガス絶縁電力機器のインパルス重畳時における電界制御効果

    伊豆淳宏,中根龍一,小島寛樹,加藤克巳,早川直樹

    第50回電気電子絶縁材料システムシンポジウム 

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    Event date: 2019.9

    Language:Japanese   Presentation type:Poster presentation  

    Venue:名古屋大学工学部IB電子情報館   Country:Japan  

  139. インバータサージ高峻度化により発生するカーボン遊離現象の検討

    吉武勇一郎,小島啓明,笠井友樹,丸山正一,小島寛樹,早川直樹

    第50回電気電子絶縁材料システムシンポジウム 

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    Event date: 2019.9

    Language:Japanese   Presentation type:Poster presentation  

    Venue:名古屋大学工学部IB電子情報館   Country:Japan  

  140. 誘電率傾斜機能材料(ε-FGM)を用いたコーン型絶縁スペーサの絶縁破壊特性

    宮崎勇作,伊豆淳宏,小島寛樹,満留博,柳瀬博雅,岡本健次,渡辺桂司,加藤克巳,早川直樹

    第50回電気電子絶縁材料システムシンポジウム 

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    Event date: 2019.9

    Language:Japanese   Presentation type:Poster presentation  

    Venue:名古屋大学工学部IB電子情報館   Country:Japan  

  141. IEEE 14母線モデルにおける複数の超電導限流器の限流協調

    森優次,小島寛樹,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 

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    Event date: 2019.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:大同大学   Country:Japan  

  142. 直流電界下の空気/固体複合絶縁系における空気中導電率の空間分布

    中根龍一,小島寛樹,早川直樹,大久保仁

    令和元年度電気・電子・情報関係学会東海支部連合大会 

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    Event date: 2019.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:大同大学   Country:Japan  

  143. エナメル皮膜の誘電損失を考慮した部分放電開始電圧の繰り返し周波数依存性

    林亮平,梶武文,小島寛樹,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 

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    Event date: 2019.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:大同大学   Country:Japan  

  144. 加圧空気中1次/2次ストリーマの絶縁破壊抑制/促進作用

    浅野竜大,小島寛樹,米須大吾,額賀淳,六戸敏昭,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 

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    Event date: 2019.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:大同大学   Country:Japan  

  145. 真空中交流部分放電による固体絶縁物上の帯電進展特性の推移

    大木駿士朗,小島寛樹,竪山智博,浅利直紀,佐々木良輔,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 

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    Event date: 2019.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:大同大学   Country:Japan  

  146. 真空中初期帯電存在時における陰極先端電界と沿面放電進展経路

    西田歩成,小島寛樹,飯塚伸介,小林将人,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 

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    Event date: 2019.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:大同大学   Country:Japan  

  147. 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 

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    Event date: 2019.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:大同大学   Country:Japan  

  148. 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 

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    Event date: 2019.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:大同大学   Country:Japan  

  149. 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 

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    Event date: 2019.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:大同大学   Country:Japan  

  150. 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 

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    Event date: 2019.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:大同大学   Country:Japan  

  151. 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 

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    Event date: 2019.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:広島工業大学 五日市キャンパス   Country:Japan  

  152. 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 

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    Event date: 2019.9

    Language:English   Presentation type:Oral presentation (general)  

    Venue:Glasgow   Country:United Kingdom  

  153. 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 

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    Event date: 2019.9

    Language:English   Presentation type:Poster presentation  

    Venue:Glasgow   Country:United Kingdom  

  154. 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 

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    Event date: 2019.8

    Language:English   Presentation type:Oral presentation (general)  

    Venue:Budapest   Country:Hungary  

  155. 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

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    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

    Other Link: https://www.webofscience.com/wos/woscc/full-record/WOS:000613001200041

  156. 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

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    Event date: 2019.5

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:まちなかキャンパス長岡   Country:Japan  

    CiNii Research

  157. 空気中不平等電界下における2次ストリーマ発生条件

    浅野竜大,小島寛樹,米須大吾,額賀淳,六戸敏昭,早川直樹

    平成31年電気学会全国大会 

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    Event date: 2019.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:北海道科学大学   Country:Japan  

  158. 共通基盤技術としての高電圧絶縁技術の将来展望

    小島寛樹,五島久司,大久保仁

    平成31年電気学会全国大会 

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    Event date: 2019.3

    Language:Japanese   Presentation type:Symposium, workshop panel (nominated)  

    Venue:北海道科学大学   Country:Japan  

  159. 高電圧絶縁技術 -9つの核心技術から紐解く歴史と将来展望-

    五島久司,小島寛樹,大久保仁

    平成31年電気学会全国大会 

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    Event date: 2019.3

    Language:Japanese   Presentation type:Symposium, workshop panel (nominated)  

    Venue:北海道科学大学   Country:Japan  

  160. SF6ガス中におけるストリーマ/リーダ放電の放射電磁波特性

    余増強,小島寛樹,早川直樹

    平成31年電気学会全国大会 

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    Event date: 2019.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:北海道科学大学   Country:Japan  

  161. 真空中スパークコンディショニングにおける微小突起の生成および溶融可能性

    近藤史規,小島寛樹,福田英昭,榊正幸,早川直樹

    平成31年電気学会全国大会 

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    Event date: 2019.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:北海道科学大学   Country:Japan  

  162. 真空インタラプタ開口モデルにおける放電パターン診断の検証

    小島寛樹,道念大樹,木村俊則,小倉健太郎,早川直樹

    平成31年電気学会全国大会 

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    Event date: 2019.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:北海道科学大学   Country:Japan  

  163. 誘電率傾斜絶縁スペーサにおける流動解析により求めた樹脂分布の妥当性検証

    今井隆浩,竹内美和,保科好一,小島寛樹,早川直樹

    平成31年電気学会全国大会 

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    Event date: 2019.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:北海道科学大学   Country:Japan  

  164. FGM絶縁スペーサの誘電率分布逆求解に関する基礎検討

    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

    平成31年電気学会全国大会 

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    Event date: 2019.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:北海道科学大学   Country:Japan  

  165. 可変配合注型法によるコーン型FGM絶縁スペーサの作製

    落合健太,伊豆淳宏,鳥前勇作,小島寛樹,加藤克巳,渡辺桂司,満留博,柳瀬博雅,岡本健次,早川直樹

    平成31年電気学会全国大会 

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    Event date: 2019.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:北海道科学大学   Country:Japan  

  166. 直流ガス絶縁電力機器の極性反転時における傾斜機能材料の電界制御効果

    伊豆淳宏,小島寛樹,加藤克巳,早川直樹

    平成31年電気学会全国大会 

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    Event date: 2019.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:北海道科学大学   Country:Japan  

  167. 超高圧超電導ケーブルの低誘電損失化に向けたTyvek®の電気絶縁特性の積層方法依存性

    山上浩輝,民部昌孝,小島寛樹,早川直樹

    平成31年電気学会全国大会 

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    Event date: 2019.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:北海道科学大学   Country:Japan  

  168. 超電導パンケーキコイルモデルのクエンチ時における液体窒素の動的絶縁破壊特性

    民部昌孝,森優次,小島寛樹,礒嶋茂樹,桑田稔,早川直樹

    平成31年電気学会全国大会 

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    Event date: 2019.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:北海道科学大学   Country:Japan  

  169. ツイストペアの部分放電開始電圧における温度および繰り返し周波数依存性

    大長勇輝,林亮平,梶武文,小島寛樹,早川直樹

    平成31年電気学会全国大会 

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    Event date: 2019.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:北海道科学大学   Country:Japan  

  170. 真空/正帯電固体絶縁物上における交流沿面放電進展特性

    大木駿士朗,小島寛樹,浅利直紀,竪山智博,佐々木良輔,早川直樹

    平成31年電気学会全国大会 

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    Event date: 2019.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:北海道科学大学   Country:Japan  

  171. 真空中沿面放電経路の初期帯電分布依存性

    西田歩成,小島寛樹,飯塚伸介,田中荘,早川直樹

    平成31年電気学会全国大会 

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    Event date: 2019.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:北海道科学大学   Country:Japan  

  172. ガス絶縁開閉装置の絶縁診断高度化に向けた部分放電の電磁波放射メカニズムの解明

    小島寛樹

    パワーアカデミー研究助成 2019年成果報告会 

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    Event date: 2019.3

    Language:Japanese   Presentation type:Public lecture, seminar, tutorial, course, or other speech  

    Venue:北海道科学大学 A棟308   Country:Japan  

  173. 樹脂充填方法が絶縁スペーサの誘電率傾斜に与える影響 -有限体積法に基づく流体解析を用いた樹脂分布の推定-

    今井隆浩,保科好一,小島寛樹,早川直樹

    電気学会誘電・絶縁材料研究会  2018.12.5  電気学会誘電・絶縁材料技術委員会

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    Event date: 2018.12

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:名古屋駅前イノベーションハブ   Country:Japan  

    CiNii Research

  174. Dynamic Breakdown Characteristics of Pancake Coil Model for Resistive Superconducting Fault Current Limiters International conference

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

    2018 Applied Superconductivity Conference 

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    Event date: 2018.10 - 2018.11

    Language:English   Presentation type:Poster presentation  

    Venue:Seattle   Country:United States  

  175. Fabrication of Permittivity Graded Materials (ε-FGM) by Flexible Mixture Casting Method International conference

    K. Ochiai, A. Izu, R. Oishi, H. Kojima, H. Mitsudome, H. Yanase, K. Okamoto, K. Kato, N. Hayakawa

    2018 IEEE Conference on Electrical Insulation and Dielectric Phenomena  2018.10.24  IEEE DEIS

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    Event date: 2018.10

    Language:English   Presentation type:Poster presentation  

    Venue:Cancun   Country:Mexico  

    For the downsizing of gas insulated power apparatus, we have proposed the electric field grading technique by 'functionally graded materials' with spatial distribution of permittivity (\varepsilon -FGM). In this paper, we fabricated post-type and truncated cone-type \varepsilon -FGM by a novel and practical technique 'flexible mixture casting method' (FMC method). We confirmed that \varepsilon -FGM by FMC method has the discharge inception voltage improvement effect by both experiment and simulation.

    DOI: 10.1109/CEIDP.2018.8544770

    Scopus

  176. Combined Effect of Temperature and Humidity of Magnet-Wires on Partial Discharge Inception Voltage under Inverter-Surge Voltage International conference

    T. Kaji, H. Asai, H. Kojima, N. Hayakawa

    2018 IEEE Conference on Electrical Insulation and Dielectric Phenomena  2018.10.24  IEEE DEIS

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    Event date: 2018.10

    Language:English   Presentation type:Poster presentation  

    Venue:Cancun   Country:Mexico  

    We investigated the combined effect of temperature and humidity on partial discharge inception voltage (PDIV) of magnet wires under repetitive surge-wave voltages. As the results, the PDIV increased as the temperature increased under uncontrolled humidity, which is peculiar under surge-wave voltage. On the other hand, the PDIV decreased lineally as the temperature increased under controlled humidity. From these results, we found that the PDIV increase under uncontrolled humidity was attributed to the effect of the relative humidity decrease corresponding to the temperature increase. Furthermore, the PDIV was also influenced by the moisture amount in insulation film. Under uncontrolled humidity, the PDIV during the temperature increase was lower than that during the temperature decrease with the hysteresis. We found two reasons for the PDIV hysteresis. One reason is the humidity increase in the air gap due to moisture evaporation from the film. Another reason is the electron emission from the film with the lower first ionization energy. Based on the above reasons, the generation probability of initial electrons during the temperature increase is higher than that during the temperature decrease, which decreases PDIV.

    DOI: 10.1109/CEIDP.2018.8544745

    Scopus

  177. Electric Field Grading by Functionally Graded Materials (FGM) for HVDC Gas Insulated Power Apparatus International coauthorship International conference

    N. Hayakawa, R. Oishi, H. Kojima, K. Kato, N. Zebouchi

    2018 IEEE Conference on Electrical Insulation and Dielectric Phenomena  2018.10.23  IEEE DEIS

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    Event date: 2018.10

    Language:English   Presentation type:Oral presentation (general)  

    Venue:Cancun   Country:Mexico  

    Functionally graded materials (FGM) have been investigated as innovative field grading and control techniques for gas insulated power apparatus such as gas insulated switchgears (GIS) and gas insulated transmission lines (GIL). We have so far verified that FGM with the spatial permittivity distribution can control the electric field distribution around GIS spacers under AC and impulse voltage stresses. In this paper, we proposed the new application of FGM for HVDC power apparatus (DC-FGM) and investigated the technical feasibility of the electric field control by DC-FGM. The calculation results revealed that DC-FGM with the spatial conductivity distribution in the spacer bulk can control the electric field distribution around the spacer in consideration of the temperature distribution under DC voltage stress.

    DOI: 10.1109/CEIDP.2018.8544834

    Scopus

  178. Estimation of Partial Discharge Inception Voltage under Repetitive Inverter Surge Voltage by Volume-Time Theory International conference

    N. Hayakawa, Y. Daicho, T. Kaji, H. Kojima

    2018 IEEE Conference on Electrical Insulation and Dielectric Phenomena  2018.10.24  IEEE DEIS

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    Event date: 2018.10

    Language:English   Presentation type:Poster presentation  

    Venue:Cancun   Country:Mexico  

    We measured the repetition frequency dependence of partial discharge inception voltage (PDIV) of twisted-pair test samples with different specifications under repetitive surge voltages with different waveforms. We also extended the PDIV estimation method with Volume-Time theory under single shot of surge voltage to that under repetitive surge voltage, in consideration of the effect of the repetition frequency on the initial electrons generation probability. The estimated and measured PDIV agreed well under repetitive surge voltage.

    DOI: 10.1109/CEIDP.2018.8544814

    Scopus

  179. Effect of Initial Electrode Surface and Breakdown Charge on Spark Conditioning in Vacuum under Non-Uniform Electric Field International conference

    H. Kojima, M. Noda, H. Fukuda, M. Sakaki, N. Hayakawa

    28th International Symposium on Discharges and Electrical Insulation in Vacuum  2018.9.25  Leibniz Institute for Plasma Science and Technology and University of Greifswald – Institute of Physics

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    Event date: 2018.9

    Language:English   Presentation type:Poster presentation  

    Venue:Greifswald   Country:Germany  

    We discuss the effect of initial cathode surface and breakdown (BD) charge on spark conditioning in a rod-plane electrode system, especially with suppressed BD charge. In the case of Cu rod cathode vs. stainless steel plane anode with a large BD charge, the saturated 50% BD field strength at the cathode tip was independent of the initial cathode surface condition, because the large BD charge led to sufficiently large melting of the cathode surface. However, in the case with suppressed BD charge not enough to remove the large weak points, the saturated BD field strength depended on the initial cathode surface condition. On the other hand, in the case of stainless steel rod cathode vs. stainless steel plane anode, the saturated BD field strength was independent of the initial cathode surface condition. In this case, the anode heating would mainly initiate BD. Since the melting of anode was the starting point of BD, the saturated BD field strength would not depend on the initial cathode surface condition regardless of BD charge.

    DOI: 10.1109/DEIV.2018.8537140

    Scopus

  180. Mechanism behind Increasing Electrostatic Charging Tendency in Aged Mineral-Oil-Immersed Pressboards International conference

    H. Morooka, A. Yamagishi, K. Kawamura, H. Kojima, N. Hayakawa

    2018 International Conference on Condition Monitoring and Diagnosis   2018.9.25  Curtin University

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    Event date: 2018.9

    Language:English   Presentation type:Oral presentation (general)  

    Venue:Perth   Country:Australia  

    The surface chemical properties of aged pressboards (PBs) were evaluated to investigate the mechanism behind the increasing tendency of electrostatic charges for diagnosing power transformers. The PBs were taken from several aged transformers, and their surface elemental composition and chemical structures were measured by X-ray photoelectron spectroscopy. The PBs properties were measured after being washed by an organic solvent to remove impregnated mineral oil. Carbon (C) and oxygen (O) atoms were mostly observed on virgin PBs surfaces; these are the atoms that compose cellulose polymer, the main component of kraft pulp. In contrast, sulfur (S) and calcium (Ca) atoms were observed on the surfaces of aged PBs in addition to the C and O atoms. Moreover, the surface densities of the Ca atoms had a good correlation with those of the S atoms. While we detected no S atoms inside the aged PBs, we observed almost the same amount of Ca atoms as in the virgin PBs. Mineral oils mainly consist of hydrocarbons, with very small amounts of components such as sulfur compounds derived from crude oil. Heat stress degrades these sulfur compounds. On the other hand, PBs made of kraft pulp contain a very small amount of metal ions, such as Ca ions. We conclude that S atoms observed on aged PB surfaces are a part of the aged sulfur compounds adsorbed from the mineral oil. The adsorption of aged sulfur compounds induced the migration of Ca ions from the inside of the PBs to the surface, which caused the surface density of the Ca ions to increase. This suggests that the accumulation of Ca ions along with the sulfur compounds led to the increasing tendency of electrostatic charges in aged PBs.

    DOI: 10.1109/CMD.2018.8535704

    Scopus

  181. Thermal-Degradation Mechanism of Mineral-Oil-Immersed Pressboards and Influence of Aging on Pressboard Properties International conference

    H. Morooka, A. Yamagishi, K. Kawamura, H. Kojima, N. Hayakawa

    2018 International Conference on Condition Monitoring and Diagnosis  2018.9.25  Curtin University

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    Event date: 2018.9

    Language:English   Presentation type:Oral presentation (general)  

    Venue:Perth   Country:Australia  

    The effects of thermal degradation and aging on the properties of mineral-oil-immersed pressboards (PBs) were studied from the viewpoint of diagnosis of power transformers. Specifically, thickness, degree of polymerization (DP), and compressive properties of oil-immersed PBs after heat-accelerated degradation in sealed containers were evaluated. The degree of crystallization (Cr) of oil-immersed PBs was then evaluated by X-ray diffraction (XRD). The evaluation results revealed that after thermal aging, DP decreased. Moreover, thickness, compressive elasticity modulus, and hysteresis loss ratio slightly decreased. Conversely, Cr slightly increased. DP of kraft paper is known to decrease after aging. Simultaneously, several compounds with low molecular weight, such as CO, CO2, and furfurals, are generated, and the tensile strength of kraft paper decreases. It is therefore assumed here that the thickness of PBs decreases very little as they generate low-molecular-weight decomposition compounds and that the decrease in DP causes a slight decrease in the compressive elasticity modulus, E. However, an increase in Cr causes a slight increase in E. As a result, the overall decrease in E is slight.

    DOI: 10.1109/CMD.2018.8535770

    Scopus

  182. 超電導限流器の絶縁設計における液体窒素の動的絶縁破壊特性

    民部昌孝,山上浩輝,小島寛樹,礒嶋茂樹,桑田稔,早川直樹

    平成30年電気学会電力・エネルギー部門大会 

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    Event date: 2018.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:徳島大学 常三島キャンパス   Country:Japan  

  183. 直流ガス絶縁電力機器への傾斜機能材料の適用可能性

    伊豆淳宏,大石涼太,小島寛樹,加藤克巳,早川直樹

    平成30年電気学会電力・エネルギー部門大会 

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    Event date: 2018.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:徳島大学 常三島キャンパス   Country:Japan  

  184. 可変配合注型法による誘電率傾斜機能材料の作製および放電開始電圧向上効果

    落合健太,伊豆淳宏,小島寛樹,満留博,柳瀬博雅,岡本健次,加藤克巳,早川直樹

    平成30年電気学会電力・エネルギー部門大会 

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    Event date: 2018.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:徳島大学 常三島キャンパス   Country:Japan  

  185. 誘電率傾斜絶縁スペーサ作製における樹脂充填挙動の流動解析を用いた可視化

    今井隆浩,岡本徹志,保科好一,落合健太,小島寛樹,早川直樹

    第49回電気電子絶縁材料システムシンポジウム 

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    Event date: 2018.9

    Language:Japanese   Presentation type:Poster presentation  

    Venue:愛媛大学 メディアセンター   Country:Japan  

  186. 加圧空気中の絶縁破壊経路に及ぼす1次ストリーマチャネルの影響

    浅野竜大,杉野一樹,小島寛樹,米須大吾,小林金也,六戸敏昭,早川直樹

    平成30年電気学会基礎・材料・共通部門大会 

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    Event date: 2018.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:イーグレひめじ   Country:Japan  

  187. Volume-Time理論による繰り返しサージ電圧下の部分放電開始電圧の推定

    大長勇輝,梶武文,小島寛樹,早川直樹

    平成30年電気学会基礎・材料・共通部門大会 

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    Event date: 2018.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:イーグレひめじ   Country:Japan  

  188. 空気中チャネル加熱絶縁破壊発生電圧の閾値の推定

    浅野竜大,小島寛樹,米須大吾,小林金也,六戸敏昭,早川直樹

    平成30年度電気・電子・情報関係学会東海支部連合大会 

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    Event date: 2018.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:名城大学   Country:Japan  

  189. 真空中スパークコンディショニング過程における溶融可能な微小突起の大きさの推定

    近藤史規,野田昌嗣,小島寛樹,福田英昭,榊正幸,早川直樹

    平成30年度電気・電子・情報関係学会東海支部連合大会 

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    Event date: 2018.9

    Language:Japanese  

    Venue:名城大学   Country:Japan  

  190. 高電圧超電導ケーブルにおける低誘電損失合成紙Tyvek®の電気絶縁特性

    山上浩輝,民部昌孝,小島寛樹,早川直樹

    平成30年度電気・電子・情報関係学会東海支部連合大会 

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    Event date: 2018.9

    Language:Japanese  

    Venue:名城大学   Country:Japan  

  191. 可変配合注型法による誘電率傾斜機能材料(ε-FGM)の作製における誘電率分布の制御性向上

    落合健太,小島寛樹,保科好一,今井隆浩,岡本徹志,早川直樹

    平成30年度電気・電子・情報関係学会東海支部連合大会 

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    Event date: 2018.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:名城大学   Country:Japan  

  192. 誘電率傾斜機能材料(ε-FGM)の電界緩和効果の絶縁スペーサ形状依存性

    伊豆淳宏,小島寛樹,満留博,柳瀬博雅,岡本健次,加藤克巳,早川直樹

    平成30年度電気・電子・情報関係学会東海支部連合大会 

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    Event date: 2018.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:名城大学   Country:Japan  

  193. 液体窒素中におけるGFRPの沿面放電特性

    民部昌孝,山上浩輝,小島寛樹,早川直樹

    平成30年度電気・電子・情報関係学会東海支部連合大会 

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    Event date: 2018.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:名城大学   Country:Japan  

  194. 乾燥空気中における部分放電形態と放射電磁波強度との相関

    余増強,小島寛樹,早川直樹

    平成30年度電気・電子・情報関係学会東海支部連合大会 

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    Event date: 2018.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:名城大学   Country:Japan  

  195. 真空中交流沿面フラッシオーバ電圧に及ぼす沿面上電界分布の影響

    大木駿士朗,小島寛樹,浅利直紀,塩入哲,佐々木良輔,早川直樹

    平成30年度電気・電子・情報関係学会東海支部連合大会 

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    Event date: 2018.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:名城大学   Country:Japan  

  196. 真空中陽極加熱絶縁破壊領域におけるコンディショニングと電極初期表面状態の関係

    野田昌嗣,大木駿士朗,小島寛樹,福田英昭,榊正幸,早川直樹

    平成30年電気学会全国大会 

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    Event date: 2018.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:九州大学 伊都キャンパス   Country:Japan  

  197. 真空中沿面放電進展過程に対する放電経路上の初期帯電分布の影響

    生田和也,小島寛樹,飯塚伸介,田中荘,早川直樹

    平成30年電気学会全国大会 

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    Event date: 2018.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:九州大学 伊都キャンパス   Country:Japan  

  198. 電界特異性を回避した絶縁スペーサにおける誘電率傾斜機能材料の電界緩和効果

    加藤克巳,満留博,柳瀬博雅,岡本健次,小島寛樹,早川直樹

    平成30年電気学会全国大会 

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    Event date: 2018.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:九州大学 伊都キャンパス   Country:Japan  

  199. 導電率傾斜機能材料(σ-FGM)による沿面放電電圧向上効果

    大石涼太,伊豆淳宏,小島寛樹,加藤克巳,早川直樹

    平成30年電気学会全国大会 

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    Event date: 2018.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:九州大学 伊都キャンパス   Country:Japan  

  200. 可変配合注型法によるポスト型誘電率傾斜機能材料の作製

    落合健太,大石涼太,小島寛樹,満留博,柳瀬博雅,岡本健次,加藤克巳,早川直樹

    平成30年電気学会全国大会 

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    Event date: 2018.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:九州大学 伊都キャンパス   Country:Japan  

  201. 抵抗型超電導限流器を模擬したパンケーキコイルモデルの動的絶縁破壊特性

    民部昌孝,山上浩輝,小島寛樹,磯嶋茂樹,桑田稔,早川直樹

    平成30年電気学会全国大会 

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    Event date: 2018.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:九州大学 伊都キャンパス   Country:Japan  

  202. インバータサージ電圧下における巻線の部分放電開始電圧に及ぼす気圧および湿度の複合的影響

    梶武文,浅井洋光,小島寛樹,早川直樹

    平成30年電気学会全国大会 

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    Event date: 2018.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:九州大学 伊都キャンパス   Country:Japan  

  203. 空気中チャネル加熱絶縁破壊における高導電率チャネルの軸方向進展

    杉野一樹,浅野竜大,小島寛樹,米須大吾,小林金也,六戸敏昭,早川直樹

    平成30年電気学会全国大会 

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    Event date: 2018.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:九州大学 伊都キャンパス   Country:Japan  

  204. インバータサージ電圧下における巻線の部分放電開始電圧に及ぼす温度および湿度の複合的影響

    梶武文,浅井洋光,小島寛樹,早川直樹

    電気学会放電/誘電・絶縁材料/高電圧合同研究会  2018.1.26  電気学会放電/誘電・絶縁材料/高電圧技術委員会

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    Event date: 2018.1

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:屋久島環境文化研修センター   Country:Japan  

    CiNii Research

  205. Electric Field Relaxation Effect of Functionally Graded Materials (FGM) with Conductive Multilayer Coating International conference

    R. Oishi, H. Kojima, N. Hayakawa, K. Kato

    2017 IEEE Conference on Electrical Insulation and Dielectric Phenomena  2017.10.23  IEEE DEIS

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    Event date: 2017.10

    Language:English   Presentation type:Oral presentation (general)  

    Venue:Fort Worth   Country:United States  

    For the insulation design of gas insulated power apparatus, the electric field grading and control are indispensable. We have proposed the application of σ-FGM (Functionally Graded Materials with spatial distribution of conductivity σ) to solid insulators as a novel technique of the electric field grading and control. In this paper, we fabricated the conductive multilayer coating for σ-FGM and investigated the electric field relaxation effect of σ-FGM on a GIS spacer surface. The fabrication results revealed that we could obtain the conductive 3-layer coating by using the dip coating method. The calculation results revealed the technical feasibility of electric field relaxation by σ-FGM with the conductive multilayer coating.

    DOI: 10.1109/CEIDP.2017.8257494

    Scopus

  206. Surface Flashover Mechanism and Its Application to Diagnosis in Vacuum Interrupter Invited International conference

    H. Kojima

    4th International Conference on Electric Power Equipment - Switching Technology  2017.10.24  State Key Laboratory of Electrical Insulation and Power Equipment, Xi’an Jiaotong University

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    Event date: 2017.10

    Language:English   Presentation type:Oral presentation (invited, special)  

    Venue:Xi'an   Country:China  

    The application of vacuum interrupters and vacuum circuit breakers for higher voltage level is strongly expected. In electrical insulation in vacuum, surface flashover on solid insulator is one of the main problems for the higher voltage vacuum interrupters. In this paper, through the review of our recent researches, we discuss on the initiation and development mechanisms of flashover in the configuration with electric field distribution almost perpendicular to the dielectrics surface. Usually, the flashover was begun by exclusive electron emission at the cathode; however, the large charging on the dielectric surface before the flashover allowed the flashover initiated by secondary electron emission avalanche to occur. The development characteristics of surface flashover agreed with the electron-stimulated outgassing mechanism. The flashover development characteristics were applied to the discharge diagnosis in vacuum, and the effectiveness of our proposed discharge discrimination method was verified.

    DOI: 10.1109/ICEPE-ST.2017.8188902

    Scopus

  207. 空気中チャネル加熱絶縁破壊に至る投入エネルギー密度

    杉野一樹,小島寛樹,大嶽敦,小林金也,六戸敏明,早川直樹

    平成29年電気学会基礎・材料・共通部門大会 

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    Event date: 2017.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:室蘭工業大学   Country:Japan  

  208. 真空中固体絶縁物上の帯電存在時における2次電子なだれ起点の沿面放電メカニズム

    生田和也,小島寛樹,飯塚伸介,土屋賢治,早川直樹

    平成29年電気学会基礎・材料・共通部門大会 

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    Event date: 2017.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:室蘭工業大学   Country:Japan  

  209. 真空中インパルス絶縁破壊における陽極注入エネルギーの推定

    野田昌嗣,小島寛樹,長谷川光佑,榊正幸,早川直樹

    平成29年電気学会基礎・材料・共通部門大会 

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    Event date: 2017.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:室蘭工業大学   Country:Japan  

  210. Volume Effect of Dynamic Breakdown Strength in LN2 for Insulation Design of Resistive Superconducting Fault Current Limiters International conference

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

    13th European Conference on Applied Superconductivity 

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    Event date: 2017.9

    Language:English   Presentation type:Poster presentation  

    Venue:Geneva   Country:Switzerland  

  211. Fault Current Limitation Coordination in Electric Power Grid with Superconducting Fault Current Limiters International conference

    N. Hayakawa, Y. Maeno, H. Kojima

    13th European Conference on Applied Superconductivity 

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    Event date: 2017.9

    Language:English   Presentation type:Poster presentation  

    Venue:Geneva   Country:Switzerland  

  212. 抵抗回路モデルによる空気中チャネル加熱絶縁破壊過程

    杉野一樹,小島寛樹,大嶽敦,小林金也,六戸敏昭,早川直樹

    平成29年度電気・電子・情報関係学会東海支部連合大会 

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    Event date: 2017.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:名古屋大学   Country:Japan  

  213. 真空中のコンディショニングにおける電極初期表面状態と放電電荷量の相関

    野田昌嗣,小島寛樹,福田英昭,榊正幸,早川直樹

    平成29年度電気・電子・情報関係学会東海支部連合大会 

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    Event date: 2017.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:名古屋大学   Country:Japan  

  214. 誘電率/導電率傾斜機能材料(ε/σ-FGM)による放電開始電圧向上の複合効果

    大石涼太,小島寛樹,加藤克巳,早川直樹

    平成29年度電気・電子・情報関係学会東海支部連合大会 

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    Event date: 2017.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:名古屋大学   Country:Japan  

  215. 可変配合注型法による誘電率傾斜機能材料(ε-FGM)の作製に向けたコンポジットの選定および混合評価

    落合健太,大石涼太,小島寛樹,加藤克巳,早川直樹

    平成29年度電気・電子・情報関係学会東海支部連合大会 

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    Event date: 2017.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:名古屋大学   Country:Japan  

  216. 高電圧超電導ケーブルに向けた低誘電損失材料における部分放電開始電界の圧力依存性

    民部昌孝,小島寛樹,早川直樹

    平成29年度電気・電子・情報関係学会東海支部連合大会 

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    Event date: 2017.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:名古屋大学   Country:Japan  

  217. 真空中固体絶縁物上の帯電分布による沿面放電開始メカニズムへの影響

    生田和也,小島寛樹,飯塚伸介,田中荘,早川直樹

    平成29年度電気・電子・情報関係学会東海支部連合大会 

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    Event date: 2017.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:名古屋大学   Country:Japan  

  218. 真空中交流部分放電における固体絶縁物上の2次電子放出係数と電荷挙動

    加藤丞,小島寛樹,早川直樹

    平成29年度電気・電子・情報関係学会東海支部連合大会 

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    Event date: 2017.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:名古屋大学   Country:Japan  

  219. 電力系統の過渡安定度を考慮した超電導限流器の限流協調

    早川直樹,前野有哉,小島寛樹

    平成29年電気学会電力・エネルギー部門大会 

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    Event date: 2017.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:明治大学 中野キャンパス   Country:Japan  

  220. 変圧器向け油含浸プレスボードの熱劣化後の圧縮特性評価

    師岡寿至,宮原秀幸,山岸明,三瓶宏幸,早川直樹,小島寛樹

    平成29年電気学会電力・エネルギー部門大会 

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    Event date: 2017.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:明治大学 中野キャンパス   Country:Japan  

  221. 真空インタラプタ内放電パターン診断における放電前シールド電位の影響

    小島寛樹,道念大樹,木村俊則,小倉健太郎,早川直樹

    平成29年電気学会電力・エネルギー部門大会 

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    Event date: 2017.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:明治大学 中野キャンパス   Country:Japan  

  222. 真空中放電電荷量を制御したコンディショニング過程における電極表面損傷の修復可能性

    野田昌嗣,小島寛樹,長谷川光佑,榊正幸,早川直樹

    平成29年電気学会電力・エネルギー部門大会 

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    Event date: 2017.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:明治大学 中野キャンパス   Country:Japan  

  223. 導電率傾斜機能材料(σ-FGM)を適用したGISスペーサの放電開始電圧の理論的推定

    大石涼太,小島寛樹,加藤克巳,早川直樹

    平成29年電気学会電力・エネルギー部門大会 

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    Event date: 2017.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:明治大学 中野キャンパス   Country:Japan  

  224. A Novel Fabrication Technique of Permittivity Graded Materials by Flexible Mixture Casting Method for GIS Spacers International conference

    N. Hayakawa, Y. Miyaji, K. Ochiai, H. Kojima, K. Kato

    20th International Symposium on High Voltage Engineering 

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    Event date: 2017.8 - 2017.9

    Language:English   Presentation type:Oral presentation (general)  

    Venue:Buenos Aires   Country:Argentina  

  225. Criteria for Channel Heating Breakdown under Non-Uniform Electric Field in Air International conference

    H. Kojima, K. Sugino, A. Ohtake, K. Kobayashi, T. Kato, T. Rokunohe

    20th International Symposium on High Voltage Engineering 

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    Event date: 2017.8 - 2017.9

    Language:English   Presentation type:Poster presentation  

    Venue:Buenos Aires   Country:Argentina  

  226. Controlling Breakdown Charge for Conditioning Procedure in Vacuum under Non-uniform Electric Field International conference

    H. Kojima, M. Noda, K. Hasegawa, M. Sakaki, N. Hayakawa

    20th International Symposium on High Voltage Engineering 

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    Event date: 2017.8 - 2017.9

    Language:English   Presentation type:Oral presentation (general)  

    Venue:Buenos Aires   Country:Argentina  

  227. 超電導限流器の開発動向と技術課題

    早川直樹,小島寛樹

    電気学会金属・セラミックス/超電導機器合同研究会  2017.7.21  電気学会金属・セラミックス/超電導機器技術委員会

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    Event date: 2017.7

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:福島工業高等専門学校   Country:Japan  

    CiNii Research

  228. 放電チャネル進展時の電流-電磁波相関に基づく電磁波放射源に関する検討

    加藤拓,杉野一樹,小島寛樹,早川直樹

    平成29年電気学会全国大会 

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    Event date: 2017.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:富山大学 五福キャンパス   Country:Japan  

  229. 真空中交流沿面フラッシオーバに及ぼす帯電極性・分布の影響

    川口王嗣,加藤丞,小島寛樹,浅利直紀,塩入哲,早川直樹

    平成29年電気学会全国大会 

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    Event date: 2017.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:富山大学 五福キャンパス   Country:Japan  

  230. 真空中固体絶縁物上の初期帯電電位分布が沿面放電メカニズムに及ぼす影響

    生田和也,小島寛樹,飯塚伸介,土屋賢治,早川直樹

    平成29年電気学会全国大会 

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    Event date: 2017.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:富山大学 五福キャンパス   Country:Japan  

  231. 空気中チャネル加熱絶縁破壊に至るエネルギーに関する考察

    杉野一樹,小島寛樹,大嶽敦,小林金也,加藤達朗,六戸敏昭,早川直樹

    平成29年電気学会全国大会 

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    Event date: 2017.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:富山大学 五福キャンパス   Country:Japan  

  232. 超電導限流器を含む電力システムの限流協調

    前野有哉,小島寛樹,早川直樹

    平成29年電気学会全国大会 

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    Event date: 2017.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:富山大学 五福キャンパス   Country:Japan  

  233. 超電導限流器の絶縁設計における液体窒素の動的絶縁破壊電界の体積効果

    石田一樹,民部昌孝,小島寛樹,礒嶋茂樹,桑田稔,早川直樹

    平成29年電気学会全国大会 

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    Event date: 2017.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:富山大学 五福キャンパス   Country:Japan  

  234. 可変配合注型法による誘電率傾斜機能材料を適用したGISスペーサの絶縁破壊電圧の推定

    宮路仁崇,大石涼太,落合健太,小島寛樹,加藤克巳,早川直樹

    平成29年電気学会全国大会 

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    Event date: 2017.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:富山大学 五福キャンパス   Country:Japan  

  235. 導電性多層コーティングによる導電率傾斜機能材料(σ-FGM)の作製・評価

    大石涼太,宮路仁崇,小島寛樹,加藤克巳,早川直樹

    平成29年電気学会全国大会 

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    Event date: 2017.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:富山大学 五福キャンパス   Country:Japan  

  236. 真空中コンディショニング過程における放電電荷量制御の効果

    野田昌嗣,小島寛樹,長谷川光佑,榊正幸,早川直樹

    平成29年電気学会全国大会 

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    Event date: 2017.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:富山大学 五福キャンパス   Country:Japan  

  237. 誘電率傾斜機能材料(ε-FGM)を用いたGISスペーサモデルの作製とSF6ガス中絶縁破壊電圧の理論的推定

    宮路仁崇,小島寛樹,加藤克巳,早川直樹

    電気学会放電/誘電・絶縁材料/高電圧合同研究会 

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    Event date: 2017.1

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:長崎大学大学院工学研究科   Country:Japan  

  238. Fabrication and Evaluation of Permittivity Graded Materials with SrTiO3 Particles and Localized Conductive Layer International conference

    Y. Miyaji, H. Kojima, K. Kato, N. Hayakawa

    2016 IEEE Conference on Electrical Insulation and Dielectric Phenomena  2016.10.18  IEEE Dielectrics and Electrical Insulation Society

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    Event date: 2016.10

    Language:English   Presentation type:Poster presentation  

    Venue:Toronto   Country:Canada  

    For the relaxation of electric field distribution around the solid insulator in power apparatus, the application of functionally graded materials (FGM) with spatial distribution of permittivity (ϵ) and conductivity (σ) is proposed. In this paper, ϵ-FGM with SrTiO3/SiO2 particles and localized conductive layers for σ-FGM are fabricated and evaluated. The fabrication results suggested that the coaxial disk-type ϵ-FGM with SrTiO3/SiO2 particles can reduce the electric field better than ϵ-FGM with TiO2/SiO2 particles. The fundamental fabrication techniques of the solid insulator with the localized conductive layers are also discussed toward σ-FGM.

    DOI: 10.1109/CEIDP.2016.7785622

    Scopus

    Other Link: https://www.webofscience.com/wos/woscc/full-record/WOS:000391639700129

  239. Electric Field Reduction by Functionally Graded Materials (FGM) with Permittivity and Conductivity Distribution International conference

    N. Hayakawa, Y. Miyaji, H. Kojima, K. Kato

    2016 IEEE Conference on Electrical Insulation and Dielectric Phenomena  2016.10.18  IEEE Dielectrics and Electrical Insulation Society

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    Event date: 2016.10

    Language:English   Presentation type:Poster presentation  

    Venue:Toronto   Country:Canada  

    Functionally graded materials (FGM) have been developed for the electric field control around the solid insulator in power apparatus. In particular, FGM with spatial distribution of permittivity (ϵ-FGM) and/or conductivity (σ-FGM) are expected to contribute to the electric field reduction leading to the size reduction of gas insulated switchgears (GIS), etc. In this paper, the electric field reduction effect of ϵ-FGM, σ-FGM and their combined ϵ/σ-FGM for a GIS spacer is investigated. Simulation results revealed the technical feasibility of electric field reduction by combined ϵ/σ-FGM for different frequencies.

    DOI: 10.1109/CEIDP.2016.7785621

    Scopus

    Other Link: https://www.webofscience.com/wos/woscc/full-record/WOS:000391639700128

  240. Discharge Pattern Discrimination for Composite Insulation System in Vacuum Interrupter International conference

    F. Kong, H. Kojima, T. Kimura, M. Tsukima, N. Hayakawa

    27th International Symposium on Discharges and Electrical Insulation in Vacuum  2016.9.22  Xi’an Jiaotong University

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    Event date: 2016.9

    Language:English   Presentation type:Oral presentation (general)  

    Venue:Suzhou   Country:China  

    DOI: 10.1109/DEIV.2016.7763963

    Other Link: https://www.webofscience.com/wos/woscc/full-record/WOS:000392206800030

  241. Optimum Breakdown Charge for Spark Conditioning in Vacuum under Non-uniform Electric Field International conference

    H. Kojima, T. Takahashi, M. Noda, K. Hasegawa, M. Sakaki, N. Hayakawa

    27th International Symposium on Discharges and Electrical Insulation in Vacuum  2016.9.19  Xi’an Jiaotong University

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    Event date: 2016.9

    Language:English   Presentation type:Oral presentation (general)  

    Venue:Suzhou   Country:China  

    Spark conditioning is one of the effective measures to improve the dielectric strength in vacuum. In this paper, we obtained the breakdown (BD) charge dependence for spark conditioning in vacuum under various non-uniform electric field and anode materials, and discussed the BD mechanism in terms of BD based on anode heating or cathode heating. Experimental results revealed that, in the case of BD based on anode heating, the longer the gap distance was, the larger the BD charge to obtain maximum dielectric strength was. On the other hand, in the case of BD based on cathode heating, the BD charge for maximum dielectric strength was smaller than that in the case of BD based on anode heating. From these results, we can estimate the optimal BD charge for the spark conditioning in vacuum.

    DOI: 10.1109/DEIV.2016.7748662

    Scopus

    Other Link: https://www.webofscience.com/wos/woscc/full-record/WOS:000402729100002

  242. UHF法における部分放電電流波形と電磁波強度との相関

    加藤拓,小島寛樹,早川直樹

    平成28年度電気・電子・情報関係学会東海支部連合大会 

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    Event date: 2016.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:豊田工業高等専門学校   Country:Japan  

  243. 超電導限流器が導入された電力システムにおける過渡安定度を考慮した限流協調

    前野有哉,小島寛樹,早川直樹

    平成28年度電気・電子・情報関係学会東海支部連合大会 

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    Event date: 2016.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:豊田工業高等専門学校   Country:Japan  

  244. 真空中コンディショニングおける陽極損耗と放電電荷量の相関

    野田昌嗣,小島寛樹,長谷川光佑,榊正幸,早川直樹

    平成28年度電気・電子・情報関係学会東海支部連合大会 

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    Event date: 2016.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:豊田工業高等専門学校   Country:Japan  

  245. 真空中交流電圧下の帯電形成による部分放電開始電圧とフラッシオーバ電圧の相関

    川口王嗣,小島寛樹,浅利直紀,塩入哲,早川直樹

    平成28年度電気・電子・情報関係学会東海支部連合大会 

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    Event date: 2016.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:豊田工業高等専門学校   Country:Japan  

  246. 直流極性反転時における真空中固体絶縁物上の電荷挙動

    生田和也,小島寛樹,早川直樹

    平成28年度電気・電子・情報関係学会東海支部連合大会 

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    Event date: 2016.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:豊田工業高等専門学校   Country:Japan  

  247. CO2ガス中におけるチャネル加熱絶縁破壊メカニズム

    杉野一樹,小島寛樹,早川直樹

    平成28年度電気・電子・情報関係学会東海支部連合大会 

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    Event date: 2016.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:豊田工業高等専門学校   Country:Japan  

  248. 液体窒素の動的絶縁破壊特性におけるギャップ長依存性

    石田一樹,小島寛樹,礒嶋茂樹,桑田稔,早川直樹

    平成28年度電気・電子・情報関係学会東海支部連合大会 

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    Event date: 2016.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:豊田工業高等専門学校   Country:Japan  

  249. 可変配合注型法による傾斜機能材料(FGM)の誘電率分布と電界緩和効果

    宮路仁崇,小島寛樹,加藤克巳,早川直樹

    平成28年度電気・電子・情報関係学会東海支部連合大会 

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    Event date: 2016.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:豊田工業高等専門学校   Country:Japan  

  250. 雷インパルス印加時における導電率傾斜機能材料(σ-FGM)の電界緩和効果

    大石涼太,宮路仁崇,小島寛樹,加藤克巳,早川直樹

    平成28年度電気・電子・情報関係学会東海支部連合大会 

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    Event date: 2016.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:豊田工業高等専門学校   Country:Japan  

  251. 高電圧超電導ケーブルの低誘電損失化に向けたポーラス紙の電気絶縁特性

    石田一樹,小島寛樹,早川直樹

    平成28年電気学会電力・エネルギー部門大会 

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    Event date: 2016.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:九州工業大学 戸畑キャンパス   Country:Japan  

  252. 真空インタラプタにおけるシールド電位の非接触測定を用いた放電パターン推定

    小島寛樹,孔飛,木村俊則,月間満,早川直樹

    平成28年電気学会電力・エネルギー部門大会 

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    Event date: 2016.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:九州工業大学 戸畑キャンパス   Country:Japan  

  253. SrTiO3/SiO2を用いた同軸ディスク型誘電率傾斜機能材料の作製およびGISスペーサの電界緩和効果

    宮路仁崇,大石涼太,小島寛樹,加藤克巳,早川直樹

    平成28年電気学会電力・エネルギー部門大会 

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    Event date: 2016.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:九州工業大学 戸畑キャンパス   Country:Japan  

  254. 放射電磁波によるノイズ環境下のGIS内部部分放電識別

    早川直樹,汲田将之,小島寛樹,吉田昌展

    平成28年電気学会電力・エネルギー部門大会 

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    Event date: 2016.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:九州工業大学 戸畑キャンパス   Country:Japan  

  255. 導電性多層コーティングによる導電率傾斜機能材料(σ-FGM)の電界緩和効果

    大石涼太,宮路仁崇,小島寛樹,加藤克巳,早川直樹

    平成28年電気学会基礎・材料・共通部門大会 

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    Event date: 2016.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:九州工業大学 戸畑キャンパス   Country:Japan  

  256. 空気中1次ストリーマ残留空間の電界が2次ストリーマ進展に及ぼす影響

    杉野一樹,小島寛樹,大嶽敦,小林金也,加藤達朗,六戸敏昭,早川直樹

    平成28年電気学会基礎・材料・共通部門大会 

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    Event date: 2016.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:九州工業大学 戸畑キャンパス   Country:Japan  

  257. SrTiO3を用いた可変配合注型法による誘電率傾斜機能材料(ε-FGM)の電界緩和効果

    宮路仁崇,大石涼太,小島寛樹,加藤克巳,早川直樹

    平成28年電気学会基礎・材料・共通部門大会 

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    Event date: 2016.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:九州工業大学 戸畑キャンパス   Country:Japan  

  258. Breakdown Characteristics and Mechanisms of Liquid Nitrogen under Transient Thermal Stress for Superconducting Fault Current Limiters International conference

    N. Hayakawa, T. Matsuoka, H. Kojima, S. Isojima, M. Kuwata

    2016 Applied Superconductivity Conference 

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    Event date: 2016.9

    Language:English   Presentation type:Poster presentation  

    Country:United States  

  259. Electrical Insulation Characteristics and Mechanisms of Low Dielectric Loss Materials for High-Voltage HTS Cables International conference

    N. Hayakawa, K. Ishida, T. Matsuoka, H. Kojima

    2016 Applied Superconductivity Conference 

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    Event date: 2016.9

    Language:English   Presentation type:Oral presentation (general)  

    Country:United States  

  260. 絶縁性液体適用機器の放電現象、劣化現象、診断技術

    森繁和,小迫雅裕,小島寛樹,福地哲生,栗原二三夫,小林広和,宮島極

    平成28年電気学会全国大会 

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    Event date: 2016.3

    Language:Japanese   Presentation type:Symposium, workshop panel (nominated)  

    Venue:東北大学 川内北キャンパス   Country:Japan  

  261. 液体窒素の動的絶縁破壊特性を考慮した超電導限流器の絶縁設計に関する考察

    松岡達矢,石田一樹,小島寛樹,礒嶋茂樹,桑田稔,早川直樹

    平成28年電気学会全国大会 

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    Event date: 2016.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:東北大学 川内北キャンパス   Country:Japan  

  262. 高電圧超電導ケーブルに向けた低誘電損失材料の部分放電開始特性

    石田一樹,松岡達矢,小島寛樹,早川直樹

    平成28年電気学会全国大会 

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    Event date: 2016.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:東北大学 川内北キャンパス   Country:Japan  

  263. 可変配合注型法を用いた誘電率傾斜機能材料(FGM)によるGISスペーサの電界緩和効果

    宮路仁崇,栗本宗明,小島寛樹,加藤克巳,早川直樹

    平成28年電気学会全国大会 

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    Event date: 2016.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:東北大学 川内北キャンパス   Country:Japan  

  264. 初期帯電を考慮した真空中沿面放電開始メカニズム

    伊吹憲哉,生田和也,小島寛樹,飯塚伸介,土屋賢治,早川直樹

    平成28年電気学会全国大会 

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    Event date: 2016.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:東北大学 川内北キャンパス   Country:Japan  

  265. TiO2/PTFEを用いた誘電率傾斜機能材料(FGM)による電力機器の電界緩和効果

    張逸凡,宮路仁崇,栗本宗明,小島寛樹,加藤克巳,早川直樹

    平成28年電気学会全国大会 

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    Event date: 2016.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:東北大学 川内北キャンパス   Country:Japan  

  266. 真空中における陰極めっきによる絶縁性能向上

    高橋達也,小島寛樹,長谷川光佑,榊正幸,早川直樹

    平成28年電気学会全国大会 

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    Event date: 2016.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:東北大学 川内北キャンパス   Country:Japan  

  267. 真空中スパークコンディショニングにおける最低破壊電圧の向上手法

    高橋達也,野田正嗣,小島寛樹,長谷川光佑,榊正幸,早川直樹

    平成28年電気学会全国大会 

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    Event date: 2016.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:東北大学 川内北キャンパス   Country:Japan  

  268. 真空インタラプタ内の放電パターンの識別手法に関する考察

    孔飛,小島寛樹,木村俊則,月間満,早川直樹

    平成28年電気学会全国大会 

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    Event date: 2016.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:東北大学 川内北キャンパス   Country:Japan  

  269. SrTiO3を用いた誘電率傾斜機能材料および局部導電性コーティングの作製・評価

    宮路仁崇,栗本宗明,小島寛樹,加藤克巳,早川直樹

    電気学会放電/誘電・絶縁材料/高電圧合同研究会 

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    Event date: 2016.1

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:宮崎公立大学 交流センター内 多目的ホール   Country:Japan  

  270. ナノ粒子添加絶縁油の電気絶縁特性

    近藤貴文,小島寛樹,花井正広,早川直樹

    電気学会静止器研究会  2015.12.11  電気学会静止器技術委員会

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    Event date: 2015.12

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:電気学会 会議室   Country:Japan  

    CiNii Research

  271. 真空中におけるスパークコンディショニングの最適放電電荷量

    高橋達也,小島寛樹,長谷川光佑,榊正幸,早川直樹

    電気学会放電/開閉保護/高電圧合同研究会  2015.11.4  電気学会放電/開閉保護/高電圧技術委員会

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    Event date: 2015.11

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:姫路市商工会議所   Country:Japan  

    CiNii Research

  272. Fluctuation and Change of Partial Discharge Inception Voltage under High Humidity for Rectangular Wire Motors International conference

    T. Wakimoto, H. Kojima, N. Hayakawa

    2015 IEEE Conference on Electrical Insulation and Dielectric Phenomena  2015.10.19  IEEE Dielectrics and Electrical Insulation Society

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    Event date: 2015.10

    Language:English   Presentation type:Oral presentation (general)  

    Venue:Ann Arbor   Country:United States  

    This paper aims to clarify the mechanism of fluctuation and change characteristics in the partial discharge inception voltage (PDIV) between motor coils constructed from rectangular wires under high humidity environments. To achieve this, the PDIV at 50Hz after pre-discharge between the coil wires were measured at 90% RH for a motor stator and test pieces, both of which were composed of rectangular wires. Electric field analyses were performed for several contact patterns between the rectangular wires for different values of surface conductivity. As the results, we clarified that the PDIV fluctuation and change in rectangular wire motors under high humidity can be caused by a superposition of the various PDIV characteristics for each contact pattern between the coil wires in the motor.

    DOI: 10.1109/CEIDP.2015.7351997

    Scopus

    Other Link: https://www.webofscience.com/wos/woscc/full-record/WOS:000370070700014

  273. 真空中の複合電極系における放電進展特性

    孔飛,中野裕介,小島寛樹,木村俊則,月間満,早川直樹

    平成27年度電気・電子・情報関係学会東海支部連合大会 

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    Event date: 2015.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:名古屋工業大学   Country:Japan  

  274. SiO2ナノ粒子添加アルキルベンゼンの交流絶縁破壊電圧におけるナノ粒子濃度依存性

    近藤貴文,小島寛樹,花井正広,早川直樹

    平成27年度電気・電子・情報関係学会東海支部連合大会 

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    Event date: 2015.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:名古屋工業大学   Country:Japan  

  275. 誘電率/導電率傾斜機能材料(ε/σ-FGM)による電界制御の複合効果

    宮路仁崇,栗本宗明,小島寛樹,加藤克巳,早川直樹

    平成27年度電気・電子・情報関係学会東海支部連合大会 

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    Event date: 2015.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:名古屋工業大学   Country:Japan  

  276. 真空中不平等電界下におけるコンディショニング飽和後の絶縁破壊機構のギャップ長依存性

    高橋達也,小島寛樹,長谷川光佑,榊正幸,早川直樹

    平成27年度電気・電子・情報関係学会東海支部連合大会 

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    Event date: 2015.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:名古屋工業大学   Country:Japan  

  277. 液体窒素の動的絶縁破壊特性における電極直径および圧力依存性

    松岡達矢,石田一樹,小島寛樹,礒嶋茂樹,桑田稔,早川直樹

    平成27年度電気・電子・情報関係学会東海支部連合大会 

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    Event date: 2015.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:名古屋工業大学   Country:Japan  

  278. 直流/インパルス重畳電圧下における真空中沿面放電特性

    伊吹憲哉,中野裕介,小島寛樹,飯塚伸介,土屋賢治,早川直樹

    平成27年度電気・電子・情報関係学会東海支部連合大会 

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    Event date: 2015.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:名古屋工業大学   Country:Japan  

  279. 局部導電性コーティングによるGISスペーサの電界緩和効果

    宮路仁崇,小島寛樹,加藤克巳,早川直樹

    平成27年電気学会基礎・材料・共通部門大会 

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    Event date: 2015.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:金沢大学 角間キャンパス 自然科学本館   Country:Japan  

  280. ナノ粒子添加絶縁油の交流絶縁破壊電圧の油中水分量依存性

    近藤貴文,小島寛樹,花井正広,早川直樹

    平成27年電気学会基礎・材料・共通部門大会 

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    Event date: 2015.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:金沢大学 角間キャンパス 自然科学本館   Country:Japan  

  281. 真空中不平等電界下におけるスパークコンディショニング特性の陽極材料およびギャップ長依存性

    高橋達也,小島寛樹,長谷川光佑,斉藤仁,榊正幸,早川直樹

    平成27年電気学会基礎・材料・共通部門大会 

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    Event date: 2015.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:金沢大学 角間キャンパス 自然科学本館   Country:Japan  

  282. 真空中の浮遊電極を介する沿面放電特性

    孔飛,中野裕介,小島寛樹,木村俊則,月間満,早川直樹

    平成27年電気学会基礎・材料・共通部門大会 

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    Event date: 2015.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:金沢大学 角間キャンパス 自然科学本館   Country:Japan  

  283. Pressure Dependence and Size Effect of Dynamic Breakdown Characteristics of LN2 under Transient Electrical/Thermal Combined Stress International conference

    N. Hayakawa, T. Matsuoka, K. Ishida, H. Kojima, S. Isojima, M. Kuwata

    12th European Conference on Applied Superconductivity 

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    Event date: 2015.9

    Language:English   Presentation type:Poster presentation  

    Country:France  

  284. 誘電率/導電率複合傾斜機能材料(ε/σ-FGM)によるGISスペーサの電界緩和効果

    宮路仁崇,石黒純也,栗本宗明,小島寛樹,加藤克巳,早川直樹

    平成27年電気学会電力・エネルギー部門大会 

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    Event date: 2015.8

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:名城大学 天白キャンパス   Country:Japan  

  285. 高電圧超電導ケーブルに向けた低誘電損失材料の電気絶縁特性

    石田一樹,松岡達矢,小島寛樹,早川直樹

    平成27年電気学会電力・エネルギー部門大会 

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    Event date: 2015.8

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:名城大学 天白キャンパス   Country:Japan  

  286. Kerr Electro-optic Field Measurement and Electrical Insulation Techniques in HVDC Oil-Pressboard Composite Insulation Systems International conference

    H. Okubo, H. Kojima, N. Hayakawa, S. Jaufer, C. Krause

    19th International Symposium on High Voltage Engineering 

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    Event date: 2015.8

    Language:English   Presentation type:Oral presentation (general)  

    Country:Czech Republic  

  287. Breakdown Mechanism Based on Secondary Streamer Propagation and Channel Heating under Non-uniform Electric Field in Air International conference

    H. Kojima, T. Kitamura, S. Goto, K. Kobayashi, T. Kato, T. Rokunohe, N. Hayakawa

    19th International Symposium on High Voltage Engineering 

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    Event date: 2015.8

    Language:English   Presentation type:Poster presentation  

    Country:Czech Republic  

  288. Reduction of Measurement Fluctuation of Partial Discharge Inception Voltage for Inverter-fed Rectangular Wire Motors International conference

    T. Wakimoto, H. Kojima, N. Hayakawa

    19th International Symposium on High Voltage Engineering 

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    Event date: 2015.8

    Language:English   Presentation type:Oral presentation (general)  

    Country:Czech Republic  

  289. Asset Management for Power Apparatus with Intelligent Grid Management System (IGMS) International conference

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

    19th International Symposium on High Voltage Engineering 

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    Event date: 2015.8

    Language:English   Presentation type:Oral presentation (general)  

    Country:Czech Republic  

  290. Breakdown and Flashover Characteristics for Discharge via Floating Electrode and Solid Insulator in Vacuum International conference

    F. Kong, Y. Nakano, H. Kojima, T. Kimura, M. Tsukima, N. Hayakawa

    19th International Symposium on High Voltage Engineering 

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    Event date: 2015.8

    Language:English   Presentation type:Oral presentation (general)  

    Country:Czech Republic  

  291. Impulse Surface Flashover Development with Transient Charging on Solid Insulators in Vacuum through Streak Image Observation International conference

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

    19th International Symposium on High Voltage Engineering 

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    Event date: 2015.8

    Language:English   Presentation type:Oral presentation (general)  

    Country:Czech Republic  

  292. Breakdown Charge Dependence for Saturation of Spark Conditioning under Non-uniform Electric Field in Vacuum International conference

    T. Takahashi, H. Kojima, K. Hasegawa, H. Saito, M. Sakaki, N. Hayakawa

    19th International Symposium on High Voltage Engineering 

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    Event date: 2015.8

    Language:English   Presentation type:Oral presentation (general)  

    Country:Czech Republic  

  293. 電力系統最適運用システム(IGMS)を用いた電力機器のアセットマネジメント

    深谷皇紀,小島寛樹,花井正広,早川直樹

    平成27年電気学会全国大会 

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    Event date: 2015.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:東京都市大学 世田谷キャンパス   Country:Japan  

  294. スパイラルアンテナによるGIS外部漏出電磁波測定

    汲田将之,小島寛樹,吉田昌展,早川直樹

    平成27年電気学会全国大会 

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    Event date: 2015.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:東京都市大学 世田谷キャンパス   Country:Japan  

  295. 真空中不平等電界下におけるスパークコンディショニング効果の陽極材料依存性

    高橋達也,小島寛樹,長谷川光佑,斉藤仁,榊正幸,早川直樹

    平成27年電気学会全国大会 

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    Event date: 2015.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:東京都市大学 世田谷キャンパス   Country:Japan  

  296. SrTiO3/BNを用いた誘電率傾斜機能材料によるGISスペーサの電界緩和効果

    張逸凡,石黒純也,栗本宗明,小島寛樹,加藤克巳,早川直樹

    平成27年電気学会全国大会 

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    Event date: 2015.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:東京都市大学 世田谷キャンパス   Country:Japan  

  297. 液体窒素の動的絶縁破壊特性における圧力依存性

    松岡達矢,石田一樹,小島寛樹,礒嶋茂樹,桑田稔,早川直樹

    平成27年電気学会全国大会 

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    Event date: 2015.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:東京都市大学 世田谷キャンパス   Country:Japan  

  298. 超純水における絶縁破壊電界の温度・流量および圧力依存性

    佐藤広治,近藤貴文,小島寛樹,花井正広,早川直樹

    平成27年電気学会全国大会 

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    Event date: 2015.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:東京都市大学 世田谷キャンパス   Country:Japan  

  299. ナノ粒子添加絶縁油の交流絶縁破壊特性におけるギャップ長依存性

    近藤貴文,佐藤広治,小島寛樹,花井正広,早川直樹

    平成27年電気学会全国大会 

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    Event date: 2015.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:東京都市大学 世田谷キャンパス   Country:Japan  

  300. N2/O2混合ガス中における1次ストリーマ進展特性

    北村卓也,後藤成彦,小島寛樹,小林金也,加藤達朗,六戸敏昭,早川直樹

    平成27年電気学会全国大会 

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    Event date: 2015.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:東京都市大学 世田谷キャンパス   Country:Japan  

  301. CO2/N2混合ガス中1次ストリーマ進展過程

    後藤成彦,北村卓也,小島寛樹,早川直樹

    平成27年電気学会全国大会 

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    Event date: 2015.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:東京都市大学 世田谷キャンパス   Country:Japan  

  302. 真空中交流部分放電における帯電形成へのアルミナ絶縁物欠陥の影響

    仲田祐希,小島寛樹,早川直樹,浅利直紀,塩入哲,松尾和宏

    平成27年電気学会全国大会 

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    Event date: 2015.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:東京都市大学 世田谷キャンパス   Country:Japan  

  303. 真空中沿面フラッシオーバ進展過程における過渡帯電分布と2次電子なだれの時間推移

    中野裕介,小島寛樹,土屋賢治,早川直樹

    平成27年電気学会全国大会 

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    Event date: 2015.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:東京都市大学 世田谷キャンパス   Country:Japan  

  304. 真空中沿面フラッシオーバ進展過程における導電チャネル形成時間

    孔飛,中野裕介,小島寛樹,木村俊則,月間満,早川直樹

    平成27年電気学会全国大会 

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    Event date: 2015.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:東京都市大学 世田谷キャンパス   Country:Japan  

  305. 平角線モータにおける部分放電開始電圧のばらつき低減方法

    脇本亨,小島寛樹,早川直樹

    電気学会誘電・絶縁材料/電線・ケ-ブル合同研究会  2015.3.13  電気学会誘電・絶縁材料/電線・ケ-ブル技術委員会

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    Event date: 2015.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:中央電気倶楽部   Country:Japan  

    CiNii Research

  306. 真空中沿面フラッシオーバ進展過程における絶縁物上過渡帯電存在時の実効的2次電子放出係数

    中野裕介,小島寛樹,土屋賢治,早川直樹

    電気学会放電/誘電・絶縁材料/高電圧合同研究会  2015.1.30  電気学会放電/誘電・絶縁材料/高電圧技術委員会

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    Event date: 2015.1

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:九州大学 伊都キャンパス   Country:Japan  

    CiNii Research

  307. 真空中不平等電界下におけるスパークコンディショニングの放電電荷量依存性

    高橋達也,小島寛樹,長谷川光佑,斉藤仁,榊正幸,早川直樹

    電気学会放電/誘電・絶縁材料/高電圧合同研究会  2015.1.30  電気学会放電/誘電・絶縁材料/高電圧技術委員会

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    Event date: 2015.1

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:九州大学 伊都キャンパス   Country:Japan  

    CiNii Research

  308. Influence of Space Charge by Primary and Secondary Streamers on Breakdown Mechanism under Non-uniform Electric Field in Air International conference

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

    2014 IEEE Conference on Electrical Insulation and Dielectric Phenomena  2014.10.20  IEEE Dielectrics and Electrical Insulation Society

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    Event date: 2014.10

    Language:English   Presentation type:Poster presentation  

    Venue:Des Moines   Country:United States  

    We have clarified that the primary and secondary streamers have a significant impact on breakdown mechanism in air. In this paper, we focused on the highly-conductive channel progress breakdown, and considered the initiation condition of highly-conductive channel from the viewpoint of the secondary streamer initiation. We revealed that the highly-conductive channel initiation voltage in the case with the grounded electrode covered by a dielectric barrier was higher than that without the barrier. We suggested that the electric field relaxation effect of the residual positive space charges formed by the primary streamer is greater than that by the secondary streamer. The highly-conductive channel is initiated from the region where the electric field relaxation is weak.

    DOI: 10.1109/CEIDP.2014.6995797

    Scopus

    Other Link: https://www.webofscience.com/wos/woscc/full-record/WOS:000352763100026

  309. Electric Field Control in Coaxial Disk-Type Solid Insulator by Functionally Graded Materials (FGM) International conference

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

    2014 IEEE Conference on Electrical Insulation and Dielectric Phenomena  2014.10.22  IEEE Dielectrics and Electrical Insulation Society

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    Event date: 2014.10

    Language:English   Presentation type:Oral presentation (general)  

    Venue:Des Moines   Country:United States  

    We have been investigating functionally graded materials (FGM) with the purpose of controlling and relaxing electric field in solid insulator of electric power apparatus. FGM is characterized by the spatial distribution of dielectric permittivity in a solid insulator, and can control the surrounding electric field distribution in power apparatus such as gas insulated switchgears (GIS) and epoxy mold transformers. In this paper, we fabricated a coaxial disk-type GLP (grading to lower permittivity)-FGM for the GIS spacer. Experimental results revealed that we could fabricate GLP-FGM with relative permittivity distribution from 8.2 to 5.3 in the coaxial disk-type spacer. According to the numerical analysis, the maximum electric field at the HV-electrode/spacer interface was reduced by 12 % for the coaxial disk-type GLP-FGM than that of the conventional spacer with uniform permittivity.

    DOI: 10.1109/CEIDP.2014.6995799

    Scopus

    Other Link: https://www.webofscience.com/wos/woscc/full-record/WOS:000352763100129

  310. Conditioning Development in Vacuum Based on Breakdown Probability Distribution International conference

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

    2014 International Symposium on Discharges and Electrical Insulation in Vacuum  2014.9.29  Bhabha Atomic Research Center and Indian Vacuum Society

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    Event date: 2014.9 - 2014.10

    Language:English   Presentation type:Oral presentation (general)  

    Venue:Mumbai   Country:India  

    Spark conditioning is important for the enhancement of insulation strength in vacuum. In order to enhance the insulation performance of vacuum circuit breakers, we have to clarify the conditioning effect and improve a conditioning procedure. In this paper, we discuss the conditioning process of Cu and stainless steel rod electrodes based on breakdown (BD) probability distribution. We applied a negative impulse voltage to a rod-plane electrode configuration. We adopted two procedures for the voltage application, i.e. up-down and 3 times methods. For the Cu rod with the up-down method, BD voltage increased by the conditioning effect, however, the minimum BD voltage did not increase or even decreased due to the damage by BD. A moderate conditioning procedure, e.g. 3 times method, could increase the minimum BD voltage as well as the stabilization of insulation strength. The Weibull analysis of the development of a BD probability distribution has enabled us to evaluate the damaging effect. Based on these results, we can discuss a suitable conditioning procedure.

    DOI: 10.1109/DEIV.2014.6961607

    Scopus

    Other Link: https://www.webofscience.com/wos/woscc/full-record/WOS:000369858100005

  311. Influence of Heat Treatment in Atmosphere for Surface Flashover Characteristics on Alumina in Vacuum International conference

    N. Asari, T. Shioiri, J. Sato, K. Matsuo, H. Kojima, N. Hayakawa

    2014 International Symposium on Discharges and Electrical Insulation in Vacuum  2014.9.30  Bhabha Atomic Research Center and Indian Vacuum Society

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    Event date: 2014.9 - 2014.10

    Language:English   Presentation type:Poster presentation  

    Venue:Mumbai   Country:India  

    Alumina Ceramics are widely used for vacuum insulation in devices such as vacuum interrupters. In development and design of vacuum interrupters, it is very important to improve the flashover characteristics on alumina ceramic surfaces in a vacuum. Thus, it is necessary to clarify the flashover mechanism on alumina ceramics in a vacuum. From past research, it is well-known that these characteristics are influenced by the insulation material, its surface condition, surface charging of the insulator and so on.(1) This paper presents the results of measurements of surface flashover characteristics and the cathode luminescence (C.L.) spectra after heat treatment in the atmosphere. These results are compared with those without heat treatment in the atmosphere. It is thus found that oxygen defects on an alumina ceramic surface decreases and the flashover voltage is improved by heat treatment in the atmosphere.

    DOI: 10.1109/DEIV.2014.6961626

    Scopus

    Other Link: https://www.webofscience.com/wos/woscc/full-record/WOS:000369858100024

  312. Transient Charging for Impulse Surface Flashover Development in Vacuum International conference

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

    2014 International Symposium on Discharges and Electrical Insulation in Vacuum  2014.9.29  Bhabha Atomic Research Center and Indian Vacuum Society

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    Event date: 2014.9 - 2014.10

    Language:English   Presentation type:Oral presentation (general)  

    Venue:Mumbai   Country:India  

    Surface discharge on solid insulator in vacuum is one of the significant issues in the development of vacuum circuit breakers and vacuum interrupters. By measuring induced current in electrostatic probes behind alumina dielectrics due to explosive electron emission (EEE) at surface flashover inception, we studied transiently formed charge characteristics on the alumina dielectrics in the development process of surface flashover. From experimental results, we found that EEE affects the flashover development through two effects of the transient charge: one is the suppression of the EEE current by the relaxation of the electric field below the cathode, the other is promotion of the secondary electron emission avalanche. In the latter effects, because of negative charge on the alumina dielectrics below the cathode, the secondary electron can fly longer along the alumina surface. As a result, the current channel on the alumina dielectrics is formed more easily.

    DOI: 10.1109/DEIV.2014.6961618

    Scopus

    Other Link: https://www.webofscience.com/wos/woscc/full-record/WOS:000369858100016

  313. Planning Maintenance Strategy for Power Apparatus and T&D System with Intelligent Grid Management System (IGMS) International conference

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

    International Conference on Condition Monitoring and Diagnosis 2014 

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    Event date: 2014.9

    Language:English   Presentation type:Oral presentation (general)  

    Country:Korea, Republic of  

  314. 誘電率傾斜機能材料(FGM)によるGISスペーサの電界制御・緩和効果

    石黒純也,栗本宗明,小島寛樹,加藤克巳,早川直樹

    平成26年電気学会電力・エネルギー部門大会 

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    Event date: 2014.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:同志社大学 京田辺キャンパス   Country:Japan  

  315. 電力系統最適運用システム(IGMS)による電力機器の保守戦略とコスト削減効果

    深谷皇紀,小島寛樹,花井正広,大久保仁,早川