Papers - SAKODA Tatsuya
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Sakoda T., Okraku-Yirenkyi Y., Sung Y., Otsubo M., Honda C.
Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers 40 ( 11 ) 6600 - 6606 2001.11
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers
In this research, both the prebreakdown phenomena and the transient processes from the prebreakdown phenomena to the glow discharge in low-pressure Ar gas, Ar/N 2 and Ar/O 2 mixtures were investigated by electrical and optical methods. The prebreakdown phenomenon in the Ar/N 2 mixture was similar to that of Ar gas, and a pulseless component has been observed. The prebreakdown phenomenon in the Ar/O 2 mixture differed from those in the Ar gas and Ar/N 2 mixture, and formed a pulse discharge. Thus, the prebreakdown phenomenon in the Ar gas has been changed to pulse discharge by mixing a small amount of O 2 gas which played an important role in the formation of pulse discharge.
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Y. O. Yirenkyi, Y. M. Sung, M. Otsubo, C. Honda, T. Sakoda
Journal of Vacuum Science & Technology A 19 ( 5 ) 2590 - 2595 2001.9
Language：Japanese Publishing type：Research paper (scientific journal)
DOI： 10.1116/1.1397467
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Diagnostics of transformer oil by elastic waves
Sakoda T., Nieda H., Ando K.
Electrical Engineering in Japan (English translation of Denki Gakkai Ronbunshi) 135 ( 1 ) 1 - 7 2001.4
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Electrical Engineering in Japan (English translation of Denki Gakkai Ronbunshi)
In the diagnostics of oil-immersed transformers, a chemical analysis of generated gases in the oil is generally performed, evaluating the kinds of gases and their quantities. This method, however, involves numerous procedures and is difficult to use in the field to diagnose the deterioration of oil. Considering the current state of the advanced information society, no deterioration in power apparatus should be permitted and the diagnosis of deterioration must be performed reliably while the equipment is energized. Therefore, we attempted to diagnose insulation oil based on analyses of elastic waves produced by a pulse discharge in the oil. This technique uses the behavior of elastic waves in liquid, in which an incident wave causes a high-frequency oscillation component with increasing gas content. In this investigation, elastic waves were detected on the outside surface of an oil tank at gas concentrations of 0 to 10%. The detected waves were analyzed by the fast Fourier transform. It was found that frequency spectra of 400 to 1000 kHz were increasingly evident when the gas concentration in oil was higher than ∼5%. This indicates that our new technique is useful for the diagnostics of oil-immersed transformers using the oscillation behavior of elastic waves produced by bubbles in oil. © 2001 Scripta Technica.
DOI： 10.1002/1520-6416(20010415)135:1<1::AID-EEJ1>3.0.CO;2-L
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Characteristics of Elastic waves Caused by Corona Discharges in an Oil Immersed Pole Transformer
T. Sakoda, H. Nieda, K. Ando
IEEE on Dielectrics and Electrical Insulation 8 ( 2 ) 276 - 283 2001.4
Language：Japanese Publishing type：Research paper (scientific journal)
DOI： 10.1109/94.919956
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Electric field calculation in composite dielectrics by first-order triangular surface charge method
Sakoda T., Nieda H., Ando K.
Electrical Engineering in Japan (English translation of Denki Gakkai Ronbunshi) 135 ( 1 ) 8 - 14 2001.4
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Electrical Engineering in Japan (English translation of Denki Gakkai Ronbunshi)
This paper proposes a technique for calculating electric fields in composite dielectrics by the first-order triangular surface charge method. The proposed technique utilizes two kinds of triangular elements, namely, conforming and nonconforming elements: these are elements whose charge density is continuous and discontinuous between the neighboring elements, respectively. We basically apply nonconforming elements at the edges of a polyhedral shape where the normal component of electric field cannot be fixed. We have computed the electric field for a spherical or a rectangular solid dielectric in the presence of a uniform field. Comparison shows that the proposed first-order method works better than the zeroth-order one, and that, in particular, the combined use of conforming and nonconforming elements produces the highest accuracy. © 2001 Scripta Technica.
DOI： 10.1002/1520-6416(20010415)135:1<8::AID-EEJ2>3.0.CO;2-Y
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FUKANO T., HORIGUCHI T., OTSUBO M., SUNG Y.M., SAKODA T., NIEDA H.
The Journal of the Institute of Electrical Installation Engineers of Japan 20 ( 10 ) 828 - 834 2000.10
Language：Japanese Publishing type：Research paper (scientific journal)
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Studies on the optimum condition for the formation of a neutral loop discharge plasma
Y. M. Sung, K. Uchino, K.. Muraoka, T. Sakoda
Journal of Vacuum Science & Technology A 18 ( 5 ) 2149 - 2152 2000.9
Language：Japanese Publishing type：Research paper (scientific journal)
DOI： 10.1116/1.1286391
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Analysis of acoustic emissions caused by the partial discharge in the insulation oil
Sakoda T., Arita T., Nieda H., Ando K.
IEEE International Conference on Conduction and Breakdown in Dielectric Liquids, ICDL 483 - 486 1999.12
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：IEEE International Conference on Conduction and Breakdown in Dielectric Liquids, ICDL
In order to diagnose the deterioration of insulation and evaluate its location in oil-filled pole transformer, measurements of elastic waves brought by corona discharges in oil were performed based on an acoustic emission (AE) technique. The detected signals in these measurements were analyzed by means of a fast Fourier transform (FFT) and their properties were discussed theoretically. It was found that the AE signals due to the Lamb waves of symmetrical mode caused in a thin steel tank could be easily recognized by the FFT analyses of initial stages of the detected AE signals. This suggests that the accuracy on location of the AE sources in the transformer would be improved. Also, it was shown that a low pass filter was effective to improve the accuracy of location.
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Acoustic emissions caused by the corona discharge in an oil-tank
Sakoda T., Arita T., Nieda H., Otsubo M., Honda C., Ando K.
IEE Conference Publication 5 ( 467 ) 1999.12
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：IEE Conference Publication
Measurements of sonic and ultrasonic waves brought by corona discharges were performed based on an acoustic emission (AE) technique, to diagnose the deterioration of insulation and its location in an oil - filled pole transformer. The detected signals in these measurements were analyzed by means of a fast Fourier transform (FFT) and their properties were discussed. It was found that the AE signals due to the Lamb waves caused in a thin steel tank can be easily recognized by the FFT analyses of initial stages of the detected AE signals. This indicates that the accuracy on location of the AE sources in the transformer can be improved. Also, it was shown that a low pass filter was effective to improve the accuracy of location.
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Studies of Elastic Waves Caused by Corona Discharges in Oil
T. Sakoda, T. Arita, H. Nieda, K. Ando, M. Otsubo, C. Honda
IEEE on Dielectrics and Electrical Insulation 6 ( 6 ) 825 - 830 1999.12
Language：Japanese Publishing type：Research paper (scientific journal)
DOI： 10.1109/94.822022
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Sakoda T., Miyao T., Uchino K., Muraoka K.
Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers 36 ( 11 ) 6981 - 6985 1997.11
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers
In order to understand plasma formation processes in a neutral loop discharge, measurements of population densities of excited levels of helium atoms were performed using laser induced fluorescence (LIF) spectroscopy. At the same time, profiles of electron density n e and electron temperature T e were measured using Thomson scattering. The results of these measurements were analyzed using a collisional-radiative model of helium atoms in the plasma. It was found that population densities of excited levels of the helium atoms were consistent with the values of n e and T e . This indicates that it is not necessary to consider an existence of a high energy electron component which may be supposed to theoretically exist in addition to the Maxwellian energy distribution function for the bulk of electrons at the measured temperature T e . Also, it was shown that the energy deposition to electrons in the vicinity of the neutral loop plays a essential role in the formation of the neutral loop discharge plasma.
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Electron temperature and density profiles in a neutral loop discharge plasma
Sakoda T., Iwamiya H., Uchino K., Muraoka K., Itoh M., Uchida T.
Japanese Journal of Applied Physics, Part 2: Letters 36 ( 1 PART A/B ) 1997.1
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics, Part 2: Letters
Thomson scattering measurements of electron temperature and density in a neutral loop discharge (NLD) plasma were performed in order to reveal electron behavior around the neutral loop. The method yielded unambiguous and reliable results, enabling quantitative analyses of particle balance to be made. The results showed that the electron temperature had a peak on the neutral loop and, in contrast, the electron density had a peak at a position radially inward from the neutral loop. We suggest that charged particles are produced by electron impact ionization of argon atoms on the neutral loop and then flow radially inward. The effect of the magnetic field strength on the NLD plasma formation is also discussed.
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Sakoda Tatsuya, Otsubo Masahisa, Honda Chikahisa, NIEDA Hiroshi
電気学会論文誌. A, 基礎・材料・共通部門誌 = The transactions of the Institute of Electrical Engineers of Japan. A, A publication of Fundamentals and Materials Society 116 ( 11 ) 953 - 958 1996.11
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：電気学会