Faculty Profiles - KOJIMA Hiroki

Presentations -

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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

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

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

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

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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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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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