Papers - SAKODA Tatsuya
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Influence of Electric Field and Fillers on Electrical Tree Development in Epoxy Resin Reviewed
Kawaguchi Teppei, Sakoda Tatsuya, Nishimura Takeshi
IEEJ Transactions on Fundamentals and Materials 143 ( 2 ) 46 - 53 2023.2
Authorship：Corresponding author Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Institute of Electrical Engineers of Japan
We investigate the influence of electric field in a void of epoxy resin with fillers on development of electrical trees. Not only observations of pits and electrical trees but also measurements of temporal variations of the number of partial discharges (PDs) and the PD magnitude were carried out. It was found that PDs with several hundred pC can be measurement by a CT sensor until the obvious formation of an electric tree is achieved in the case of epoxy resin without fillers. Additionally, when electric field of the tip of a pit is the almost same as the withstand electric field of the epoxy resin, electrical tree and breakdown occur in a very short time. The development of electrical tree is disturbed by fillers in epoxy resin, and the required time for breakdown is much longer than that of epoxy resin without fillers.
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Influence of impulse corona discharge on discharge time lag of a surge arrester with a spark gap Reviewed
Sakoda T., Kubo K., Mizutani M., Chiba T., Kasuga Y., Fukano T.
Journal of Electrostatics 121 2023.1
Authorship：Lead author Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Electrostatics
ZnO surge arrester with a spark gap is used for reducing electrical failures in power distribution systems of Japan. The high responsiveness, the low residual voltage, and the stable operating voltage are required for the arresters. However, the discharge time lag generally occurs in a spark gap. In this study, measurements of V-t characteristics and observations of optical emissions from impulse corona discharges generated at a newly designed small step edge on an inclined plane of each electrode were carried out. The small step edge made the discharge time lag and the standard deviation small. Based on the results, we indicated that the impulse corona discharge improves the discharge time lag of the sparkover.
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Short-time Evaluation Technique of Degradation Degree by Surface Discharge Reviewed
Khaing M.T., Yoshimura K., Sakoda T., Goto S., Anjiki T., Chiba T., Kasuga Y.
IET Conference Proceedings 2023 ( 46 ) 992 - 996 2023
Publishing type：Research paper (scientific journal) Publisher：IET Conference Proceedings
Silicone rubber (SiR) is being adopted as the housing material for insulators. However, the hydrophobic property and the recovery characteristic might be degraded under multiple stress. As one of the degradation diagnosis techniques for the long-term reliability evaluation of SiR, we have proposed a continuous salt fog test in which 20 - times salt fog aging tests by applying ac voltage for 3 h were repeatedly carried out. However, it takes a much longer time. In this study, we examined a novel technique by using surface discharges (SDs) instead of the previous technique. The SDs were generated on the aged SiR surface for 10 s, and then the hydrophobicity recovery time obtained by measuring the contact angle of a water droplet on the SiR was evaluated. The results indicate a possibility that the hydrophobicity recovery time after the SD treatment can refer to the degradation degree of SiR without causing physical and chemical damage.
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Effect of Supercapacitor on Transient Response of Thermoelectric Generation Systems Reviewed
鳥原 亮, 迫田 達也, 林 則行
宮崎大学工学部紀要 51 69 - 77 2022.11
Language：English Publishing type：Research paper (scientific journal) Publisher：宮崎大学工学部
Thermoelectric generators (TEGs) are being used for the harvesting of wasted thermal energy because the TEG converts the temperature difference into the electrical energy. The purpose of this research is to investigate the transient response of electrical properties for TEG systems when the electric load is connected to them. In this study, two kinds of TEG systems were employed; one installed with only a single thermoelectric module (TEM), and another installed with four TEMs and two DC/DC converters (one converter is to track the MPP of the TEMs, and another converter is to regulate the output voltage). An electric double layer capacitor (EDLC) also called a supercapacitor unit was used to improve the transient performance of the two kinds of TEG systems. A filament electric lamp with a non-linear nature of its resistance was employed to investigate the transient responses of the two TEG systems.
Based on the experimental results, the electrical characteristics (voltage, current and power) are studied, and the transient responses of voltage and current as a function of time are analyzed, and the effect of installing the EDLC to the TEG systems are discussed. It is found that the TEG with only a single TEM has high transient responses of voltage and current, large TEG voltage drop during the transient period. Installation of EDLC to the TEG systems can reduce the transient responses of voltage and current and can also reduce TEG voltage drop during the transient period. It is also found that EDLC increases the maximum power at proper load. -
Optimal arrangement of TEV sensors for diagnosing oil-filled transformer Reviewed
Sakoda Tatsuya, Mori Wataru
Memoirs of Faculty of Engineering, University of Miyazaki 51 79 - 81 2022.11
Language：Japanese Publishing type：Research paper (scientific journal)
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Effect of Supercapacitor on Transient Response of Thermoelectric Generation Systems
Tin Tin Cho, Ryo Torihara, Tatsuya Sakoda, Noriyuki Hayashi
宮崎大学工学部紀要 ( 51 ) 69 - 77 2022.11
Language：English Publishing type：Research paper (bulletin of university, research institution)
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Degradation Monitoring of Silicone Rubber Used for Insulators Reviewed
May Thin Khaing, Kosei Yoshimura, Tatsuya Sakoda, Junki Oasa, Shoichi Higashiyama, and Yuko Inaoka
9th International Conference on Condition Monitoring and Diagnosis 2022 382 - 386 2022.11
Authorship：Corresponding author Language：English Publishing type：Research paper (international conference proceedings)
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Development of Detection Technique of Residual-charges by Inductive Current Pulse Reviewed
Nakaguchi Ryusei, Sakoda Tatsuya, Kataoka Tatsuya, Okamoto Dai, Tsuiki Ushio, Futagawa Kazuhiro, Satoh Hideaki
IEEJ Transactions on Fundamentals and Materials 142 ( 7 ) 345 - 346 2022.7
Authorship：Corresponding author Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Institute of Electrical Engineers of Japan
To establish a novel section locating technique of water-tree degraded 22 kV cross - linked polyethylene (XLPE) cable, we measured the injected current pulse with residual - charges due to water trees in a XLPE cable which was used for 27 years and removed after performing residual charge measurement. It was found that the current/voltage pulse injected at a prescribed value of AC voltage may carry residual charges reflecting water tree length.
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Change in V-I Characteristics of Schottky Barrier Diodes when Application of Standard Lightning Impulse Voltage Causes Breakdown of Them Reviewed
Swezin Linnhtet, May Oo Khin, Ryo Torihara, Tatsuya Sakoda, Noriyuki Hayashi
The International Council on Electrical Engineering Conference 2022 635 - 641 2022.6
Language：English Publishing type：Research paper (international conference proceedings)
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Voltage and Current Characteristics of Schottky Barrier Diodes when Application of Standard Lightning Impulse Voltage Causes Breakdown of Them Reviewed
Tinzar Win ko, May Oo Khin, Ryo Torihara, Tatsuya Sakoda, Noriyuki Hayashi
The International Council on Electrical Engineering Conference 2022 642 - 649 2022.6
Language：English Publishing type：Research paper (international conference proceedings)
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Effective Measurement of Elastic Waves due to Partial Discharges in Oil-immersed Transformer Reviewed
Mori Wataru, Sakoda Tatsuya, Sato Masaharu, Takei Katsutoshi
IEEJ Transactions on Fundamentals and Materials 142 ( 3 ) 124 - 125 2022.3
Authorship：Corresponding author Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Institute of Electrical Engineers of Japan
Based on numerical and experimental analyses of sound pressure distributions owing to partial discharges in oil-immersed transformer, we propose an effective arrangement of acoustic emission sensors. The sensor arrangement at the surface edge of the transformer housing allows us to minimize the required time for diagnosing.
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On-line PD Monitoring System (PDLOOK) for XLPE Cables Reviewed
Akaiwa S., Miyagawa K., Nakashima T., Sakoda T., Miyake T., Takayama A.
2022 9th International Conference on Condition Monitoring and Diagnosis, CMD 2022 703 - 706 2022
Publishing type：Research paper (scientific journal) Publisher：2022 9th International Conference on Condition Monitoring and Diagnosis, CMD 2022
We have developed a continuous remote monitoring system that can monitor partial discharge (PD) trends for a long period of time, which greatly saves the labor in operating. An Edge terminal uploads a signal obtained from the high frequency CT attached to the power cable to a cloud system. In this process, a PD-like signal is effectively discriminated from a large amount of acquired data by using a noise filtering function. The signal data uploaded on the cloud system is PD-judged by AI, and a learning cycle function improves the AI judgment accuracy.
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Degradation Monitoring of Silicone Rubber Used for Insulators Reviewed
Khaing M.T., Yoshimura K., Sakoda T., Oasa J., Higashiyama S., Inaoka Y.
2022 9th International Conference on Condition Monitoring and Diagnosis, CMD 2022 382 - 386 2022
Publishing type：Research paper (scientific journal) Publisher：2022 9th International Conference on Condition Monitoring and Diagnosis, CMD 2022
Electrical insulation equipment such as insulators contributes to reduction of electrical fault owing to overvoltage. Polymeric material such as silicone rubber (SiR) is gradually replacing porcelain. However, in Japan the application of polymeric material is limited because there are concerns about the hydrophobicity degradation and the decrease of insulation performance. Therefore, it is important to investigate not only pollution effect on the insulation performance but also the long-term reliability of polymeric material. Additionally, it is desired to establish an easy diagnostic technique which can grasp the degree of degradation of polymeric material. To evaluate the degradation degree of SiR of insulators arranged for a long period of time in the coastal area, we first characterized the surface of aged SiR specimen cut out from a line post insulator arrange for 20 years in the coastal area by using the attenuated total internal reflection Fourier transform infrared spectroscopy (ATR-FTIR). Next, we repeatedly performed a salt fog aging test against SiR specimens. Then, the surface hydrophobicity and the leakage current were evaluated. From the ATR-FTIR analysis, it was found that the reflectance peaks due to Si-CH3 symmetric bending of aged specimen decreases in comparison with those of unused specimen. The continuous salt fog aging test investigated that a required time for recovering hydrophobicity is a good index for degradation diagnosis because the required times for recovering hydrophobicity of SiR used for 20 years are much longer than that of unused SiR.
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Nakakoga Y., Tada Y., Sakoda T., Tazawa K., Ichikawa H.
Electronics and Communications in Japan 104 ( 4 ) 2021.12
Authorship：Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Electronics and Communications in Japan
To develop a sterilization method for controlling post-harvest stem-end rot of mango, we examined to sterilize fungi on peduncle by using the dielectric barrier discharge (DBD). Additionally, to investigate the sterilization factors, we performed sterilization against stem-end rot on agar medium by using the DBD generated in air, argon gas, or oxygen gas. It was found that the DBD can sterilize fungi with high probability. Ultra-violet ray and O3 do not contribute to the sterilization. High energy electrons, and radicals such as O and OH play an essential role for the sterilization.
DOI： 10.1002/ecj.12325
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Evaluation of Surface Degradation of Silicone Rubber by Continuous Salt-fog Aging Test Reviewed
Adachi Kohei, Miyake Takuma, Sakoda Tatsuya
IEEJ Transactions on Fundamentals and Materials 141 ( 10 ) 590 - 596 2021.10
Authorship：Corresponding author Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Institute of Electrical Engineers of Japan
<p>To evaluate the long-term reliability of polymeric material used for housing material of electric power apparatus, we continuously performed a salt-fog aging test against silicone rubber (SiR) specimens cut out from line post insulators arranged for 10 and 20 years in the coastal area. Then, the surface hydrophobicity and the leakage current were evaluated. The results showed that a required time for recovering hydrophobicity and a discharge ignition time until the leakage current is detectable are good indexes for degradation diagnosis. Especially, the required time for recovering hydrophobicity is useful. The required times for recovering hydrophobicity of SiR used for 10 and 20 years were much longer than that of unused SiR.</p>
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迫田 達也
宮崎大学工学部紀要 50 105 - 112 2021.9
Language：English Publishing type：Research paper (scientific journal) Publisher：宮崎大学工学部
The purpose of this study is to assist the operation and maintenance of PV systems by studying the resistive conditions of bypass diode used in PV modules and to develop the diagnosis and on-line monitoring system for small and medium scale PV systems. This paper analyzes the breakdown and non-breakdown
characteristics of Schottky diodes and PN Junction diodes by application of various ranges of voltages by Lightning surge simulator (LSS). In this study, we compare and discuss the numerical data of experimental results obtained under variable voltage applications of LSS are compared for both diodes on the resistive
characteristics after breakdown, waveforms of voltage and current and the behaviors of dynamic curves.
An applied voltage, on which the breakdown of diode takes place and dramatic change in I-V characteristics occurs, is called “critical voltage (Vc)”. From the study, it was observed that the magnitude of critical voltage (Vc) of PN junction diodes is higher than that of Schottky diodes in reverse direction although
there is almost the same in forward direction. The authors are also probing that the possibility of more sensitive monitoring and diagnosis system for the resistive bypass diode in PV system based on numerical simulation results. The great difference of Vc is reflected for the dynamic relationship between voltage and current in reverse biasing for both diodes. -
Voltage Profi les on HV Distribution Lines with Various Network Confi gurations and Customers Reviewed
迫田 達也
宮崎大学工学部紀要 50 95 - 103 2021.9
Language：English Publishing type：Research paper (scientific journal) Publisher：宮崎大学工学部
Electrical power system reliability is a critical issue for utilities and power loss occurred in transmission and distribution network is a must consideration. Electrical distribution system is the largest portion of network in the electrical power system. There is voltage drop on long HV distribution line (D/L) due to heavy load consumption, absent of voltage regulation, as well as poor power factor collection on long HV D/L. Therefore, phase advancing capacitors (Shunt Capacitor, SCs) are installed in parallel with customer loads for voltage improvement and power factor correction. However, these SCs, sometimes, lead to Ferranti effect, especially at the very lightly loaded condition. Moreover, in recent years, the introduction of photovoltaic power generation systems (PV systems) into HV D/L has developed rapidly and may cause the unacceptable voltage variation on HV D/L.
In this study, a virtual 6.6 kV long distance (20 km) HV D/L without PV system supported from Kyushu Electric Power Company (Qden) in Miyazaki branch, is introduced. In this long distance HV D/L, a 20 MVA transformer, three static voltage regulators (SVRs), and 50 customer loads are included. For very lightly loaded condition, the effects of SCs detachment area on the voltage profiles of HV D/L are numerically investigated and discussed. Moreover, the optimal location is proposed to change the suitable SVR for the purpose of upgrading voltage drop in heavy loaded condition.
Then, voltage profiles of different lengths (20.3 km for long and 8.70 km for short) HV D/Ls with PV system installing SCs at customer’s side and different load capacity are discussed. Furthermore, the conditions of flowing line current on HV D/L with PV system for different load locations are explained with phasor diagram. A program based on the Newton Raphson method was coded for the power flow calculation. -
Dynamic I-V Characteristics of Schottky Diodes and PN Junction Diodes When Lightning Impulse Voltage Is Applied on Them
May Oo KHIN, Ryo TORIHARA , Tatsuya SAKODA, Noriyuki HAYASHI
Memoirs of faculty of engineering university of miyazaki 50 105 - 112 2021.9
Language：English Publishing type：Research paper (bulletin of university, research institution)
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Voltage Profiles on HV Distribution Lines with Various Network Configurations and Customers
May Thin KHAING, Tatsuya SAKODA, Noriyuki HAYASHI
Memoirs of faculty of engineering university of miyazaki 50 95 - 104 2021.9
Language：English Publishing type：Research paper (bulletin of university, research institution)
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Nakakoga Yuta, Tada Yoichiro, Sakoda Tatsuya, Tazawa Kazutoshi, Ichikawa Hiroyuki
IEEJ Transactions on Fundamentals and Materials 141 ( 6 ) 385 - 390 2021.6
Authorship：Corresponding author Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Institute of Electrical Engineers of Japan
<p>To develop a sterilization method for controlling post-harvest stem-end rot of mango, we examined to sterilize fungi on peduncle by using the dielectric barrier discharge (DBD). Additionally, to investigate the sterilization factors, we performed sterilization against stem-end rot on agar medium by using the DBD generated in air, argon gas or oxygen gas. It was found that the DBD can sterilize fungi with high probability. Ultra-violet ray and O<sub>3</sub> don’t contribute to the sterilization. High energy electrons, and radicals such as O and OH play an essential role for the sterilization.</p>