研究者詳細 - 小島　寛樹

講演・口頭発表等 - 小島　寛樹

分割表示 795 件中 201 - 220 件目／全件表示 >>

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

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

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

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

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

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年12月5日電気学会誘電・絶縁材料技術委員会

Dynamic Breakdown Characteristics of Pancake Coil Model for Resistive Superconducting Fault Current Limiters 国際会議

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

2018 Applied Superconductivity Conference

Fabrication of Permittivity Graded Materials (ε-FGM) by Flexible Mixture Casting Method 国際会議

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年10月24日 IEEE DEIS

開催年月日： 2018年10月

記述言語：英語会議種別：ポスター発表

開催地：Cancun 国名：メキシコ合衆国

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

Combined Effect of Temperature and Humidity of Magnet-Wires on Partial Discharge Inception Voltage under Inverter-Surge Voltage 国際会議

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

2018 IEEE Conference on Electrical Insulation and Dielectric Phenomena 2018年10月24日 IEEE DEIS

開催年月日： 2018年10月

記述言語：英語会議種別：ポスター発表

開催地：Cancun 国名：メキシコ合衆国

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

Electric Field Grading by Functionally Graded Materials (FGM) for HVDC Gas Insulated Power Apparatus 国際共著国際会議

N. Hayakawa, R. Oishi, H. Kojima, K. Kato, N. Zebouchi

2018 IEEE Conference on Electrical Insulation and Dielectric Phenomena 2018年10月23日 IEEE DEIS

開催年月日： 2018年10月

記述言語：英語会議種別：口頭発表（一般）

開催地：Cancun 国名：メキシコ合衆国

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

Estimation of Partial Discharge Inception Voltage under Repetitive Inverter Surge Voltage by Volume-Time Theory 国際会議

N. Hayakawa, Y. Daicho, T. Kaji, H. Kojima

2018 IEEE Conference on Electrical Insulation and Dielectric Phenomena 2018年10月24日 IEEE DEIS

開催年月日： 2018年10月

記述言語：英語会議種別：ポスター発表

開催地：Cancun 国名：メキシコ合衆国

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

Effect of Initial Electrode Surface and Breakdown Charge on Spark Conditioning in Vacuum under Non-Uniform Electric Field 国際会議

H. Kojima, M. Noda, H. Fukuda, M. Sakaki, N. Hayakawa

28th International Symposium on Discharges and Electrical Insulation in Vacuum 2018年9月25日 Leibniz Institute for Plasma Science and Technology and University of Greifswald – Institute of Physics

開催年月日： 2018年9月

記述言語：英語会議種別：ポスター発表

開催地：Greifswald 国名：ドイツ連邦共和国

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

Mechanism behind Increasing Electrostatic Charging Tendency in Aged Mineral-Oil-Immersed Pressboards 国際会議

H. Morooka, A. Yamagishi, K. Kawamura, H. Kojima, N. Hayakawa

2018 International Conference on Condition Monitoring and Diagnosis 2018年9月25日 Curtin University

開催年月日： 2018年9月

記述言語：英語会議種別：口頭発表（一般）

開催地：Perth 国名：オーストラリア連邦

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

Thermal-degradation Mechanism of Mineral-oil-immersed Pressboards and Influence of Aging on Pressboard Properties 国際会議

H. Morooka, A. Yamagishi, K. Kawamura, H. Kojima, N. Hayakawa

2018 International Conference on Condition Monitoring and Diagnosis 2018年9月25日 Curtin University

開催年月日： 2018年9月

記述言語：英語会議種別：口頭発表（一般）

開催地：Perth 国名：オーストラリア連邦

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

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