研究者詳細 - 小島　寛樹

論文 - 小島　寛樹

分割表示 116 件中 81 - 100 件目／全件表示 >>

Partial Discharge Activity in Electrical Insulation for High Temperature Superconducting (HTS) Cables 査読有り国際誌

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

IEEE Transactions on Dielectrics and Electrical Insulation 15 巻 ( 3 ) 頁： 647 - 654 2008年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：IEEE

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.

DOI： 10.1109/TDEI.2008.4543100

Quench-Induced Partial Discharge Characteristics of HTS Cables 査読有り国際誌

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

Journal of Physics: Conference Series 97 巻 ( 1 ) 頁： 012053 2008年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：IOP Publishing

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.

DOI： 10.1088/1742-6596/97/1/012053

Self-recovery Characteristics of High-Tc Superconducting Fault Current Limiting Transformer (HTc-SFCLT) with 2G Coated Conductors 査読有り国際共著国際誌

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

Journal of Physics: Conference Series 97 巻 ( 1 ) 頁： 012154 2008年3月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：IOP Publishing

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.

DOI： 10.1088/1742-6596/97/1/012154

Breakdown Characteristics of N₂O Gas Mixtures for Quasi-uniform Electric Field under Lightning Impulse Voltage 査読有り国際誌

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

IEEE Transactions on Dielectrics and Electrical Insulation 14 巻 ( 6 ) 頁： 1492 - 1497 2007年12月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：IEEE

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.

DOI： 10.1109/TDEI.2007.4401233

Electrical Insulation Characteristics of HTS Cables under Quench-Induced Thermal Stress Condition 査読有り国際誌

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

IEEE Transactions on Applied Superconductivity 17 巻 ( 2 ) 頁： 1660 - 1663 2007年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：IEEE

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.

DOI： 10.1109/TASC.2007.899968

Thermal Runaway Characteristics of Bi2212 Coil for Conduction-cooled SMES 査読有り国際誌

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

IEEE Transactions on Applied Superconductivity 17 巻 ( 2 ) 頁： 1959 - 1962 2007年6月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：IEEE

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. © 2007 IEEE.

DOI： 10.1109/TASC.2007.898492

High-Tc Superconducting Fault Current Limiting Transformer (HTc-SFCLT) with 2G Coated Conductors 査読有り国際共著国際誌

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

IEEE Transactions on Applied Superconductivity 17 巻 ( 2 ) 頁： 1768 - 1771 2007年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：IEEE

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.

DOI： 10.1109/TASC.2007.897813

N₂O混合ガスの絶縁特性におけるシナジズム効果査読有り

早川直樹，木下修，小島寛樹，遠藤奎将，吉田昌展，小川達也，大久保仁

電気学会論文誌Ｂ（電力・エネルギー部門誌） 126 巻 ( 11 ) 頁： 1164 - 1170 2006年11月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：一般社団法人電気学会

This paper discusses partial discharge (PD) and breakdown (BD) characteristics of N 2O gas and N 2O gas mixtures as SF 6 substitutes as a function of gas pressure and N 2O 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 2O30%/CO 270% and N 2O30%/CO 250%/O 220% gas mixtures under quasi-uniform electric field. Furthermore, corona stabilization effect in N 2O30%/CO 270% gas mixtures under non-uniform electric field was discussed and suggested to be activated due to the combination of electronegative N 2O and CO 2 gases.

DOI： 10.1541/ieejpes.126.1164

Simulation of Electrical and Thermal Behavior of High Temperature Superconducting Fault Current Limiting Transformer (HTc-SFCLT) 査読有り国際共著国際誌

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

Journal of Physics: Conference Series 43 巻頁： 950 - 953 2006年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：IOP Publishing

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.

DOI： 10.1088/1742-6596/43/1/232

Electrical and Thermal Characteristics of Bi2212/Ag HTS Coils for Conduction-cooled SMES 査読有り国際誌

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

Journal of Physics: Conference Series 43 巻頁： 813 - 816 2006年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：IOP Publishing

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.

DOI： 10.1088/1742-6596/43/1/198

Impulse and AC Partial Discharge Inception and Breakdown Characteristics of LN₂/Polypropylene Laminated Paper Composite Insulation System 査読有り国際誌

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

IEEE Transactions on Dielectrics and Electrical Insulation 13 巻 ( 3 ) 頁： 664 - 669 2006年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：IEEE

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.

DOI： 10.1109/TDEI.2006.1657982

Temperature Dependence of Critical Current at 4.2 K-55 K of Conduction-cooled Bi2212/Ag Wires for SMES 査読有り国際誌

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

IEEE Transactions on Applied Superconductivity 15 巻 ( 2 ) 頁： 2550 - 2553 2005年6月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：IEEE

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.

DOI： 10.1109/TASC.2005.847646

Dielectric Characteristics of HTS Cables Based on Partial Discharge Measurement 査読有り国際誌

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

IEEE Transactions on Applied Superconductivity 15 巻 ( 2 ) 頁： 1802 - 1805 2005年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：IEEE

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.

DOI： 10.1109/TASC.2005.849292

Recovery Characteristics after Current Limitation of High Temperature Superconducting Fault Current Limiting Transformer (HTc-SFCLT) 査読有り国際共著国際誌

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

IEEE Transactions on Applied Superconductivity 15 巻 ( 2 ) 頁： 1859 - 1862 2005年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：IEEE

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.

DOI： 10.1109/TASC.2005.849314

Formation of Deep Potential Well and its Structural Transition in Small Tokamak Device 国際誌

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

Europhysics Conference Abstracts 28G 巻頁： P-5.075 2004年7月

小型トカマク放電の高機能化に関する研究査読有り

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年3月

Formation and Dynamics of Very Deep Negative Potential Well in the Small Tokamak Device CSTN-IV 査読有り国際誌

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

Czechoslovak Journal of Physics 53 巻 ( 10 ) 頁： 895 - 902 2003年10月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Springer Nature

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.

DOI： 10.1023/A:1026392406717

Spatiotemporal Behavior of Hydrogen Recycling due to the Rotating Magnetic Field 査読有り国際誌

H. Kojima, S. Takamura

Japanese Journal of Applied Physics 42 巻 ( 9A ) 頁： 5797 - 5798 2003年9月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：The Japan Society of Applied Physics

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.

DOI： 10.1143/JJAP.42.5797

Structural Dynamics of Deep Negative Potential Well Formation in Small Tokamak Device CSTN-IV 国際誌

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

Europhysics Conference Abstracts 27A 巻頁： P-2.130 2003年9月

Effects of Rotating Helical Magnetic Field on Inhomogeneities of Hydrogen Recycling in a Tokamak Discharge. 査読有り国際誌

H. Kojima, S. Takamura

Japanese Journal of Applied Physics 41 巻 ( 11A ) 頁： 6557 - 6562 2002年11月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：The Japan Society of Applied Physics

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.

DOI： 10.1143/JJAP.41.6557

　前のページ - 次のページ　

1
2
3
4
5
6