Faculty Profiles - KOJIMA Hiroki

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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

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

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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

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

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

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

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

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

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

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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

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

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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

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

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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

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

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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

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

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

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

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

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

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

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

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

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

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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