Papers - SAKODA Tatsuya
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Partial Discharge and Electrical Treeing Phenomena Within Two Spherical Voids in Epoxy Resin Reviewed
Htet S.Z.L., Kondo T., Khaing M.T., Sakoda T., Harada Y., Takei K., Ikeda M., Miyazaki K.
2024 10th International Conference on Condition Monitoring and Diagnosis, CMD 2024 358 - 361 2024.10
Authorship：Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：2024 10th International Conference on Condition Monitoring and Diagnosis, CMD 2024
Partial discharge (PD) and electrical treeing phenomena in an epoxy resin electrode which had two spherical voids and the insulation paper were investigated. The alignment of the two voids was vertical against the applied electric field direction, and experiments with not only two voids of the same size (diameter of 1 mm) but also two voids of different size (diameters of 1 mm and 1.5 mm) were carried out. AC high voltage was applied until the breakdown occurred in the epoxy resin electrode. PD and electrical treeing phenomena were detected by using a high frequency current transformer (HF-CT) sensor, a transient earth voltage (TEV) sensor and an ultra-high frequency (UHF) sensor. We here focused on variations of the number of PDs per unit time and frequency components of detected signals with the elapsed time from the voltage application. As a result, we investigated a unique electrical tree development characteristic which differed in the size of two voids. Although the electrical tree development was temporarily decelerated by the insulation paper, the breakdown suddenly occurred from a point of high electric field in the insulation paper. Additionally, we investigated the temporal variations of the number of PDs which differed in the combination of the void size.
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Diagnosis of Degradation Degree on SiR Surface Used for Insulator by Surface Discharge Reviewed
Khaing M.T., Miyake T., Sakoda T., Goto S., Anjiki T., Chiba T., Kasuga Y.
2024 10th International Conference on Condition Monitoring and Diagnosis, CMD 2024 386 - 389 2024.10
Authorship：Corresponding author Publishing type：Research paper (scientific journal) Publisher：2024 10th International Conference on Condition Monitoring and Diagnosis, CMD 2024
Silicone rubber (SiR) insulators have been mostly preferred for high-voltage transmission and distribution lines because of their superior hydrophobicity characteristic. Hydrophobicity of SiR insulators may be, however, degraded by multiple stresses and may eventually lead to dry band arcing. Hence, a diagnostic technique of degradation degree on SiR surface will be useful for the long-term maintenance of SiR insulators. In this study, the artificially degraded layers were first made on two SiR surfaces by red clay adhesion, UV irradiation and surface heating. To diagnose the degradation degree on the SiR surface, an unused SiR surface, two artificially degraded SiR surfaces (Sample A (UV, Heating) and Sample B (Heating, UV)) and two aged SiR surfaces (10-year-aged and 20-year-aged) were exposed to a surface discharge (SD) source. The applied voltage and treatment time of SD against the experimental SiR surfaces were 8 kVp-p and 10 s, respectively. After the SD treatment, the hydrophobicity recovery time of each experimental SiR surface was evaluated with the contact angle of a water droplet on the SiR surface. Then, monitoring of water-repellent maintenance (i.e., the contact angle of water droplets on the SiR surface remaining in stable condition) on each experimental SiR surface was also conducted. It was found that the hydrophobicity recovery times and water-repellent change times (duration of contact angle of water droplets on the SiR surface in stable condition) of Sample A (UV, Heating) and Sample B (Heating, UV) were similar to those of 10-year-aged and 20-year-aged SiR surfaces, respectively. Additionally, water-repellent change times of Sample B (Heating, UV) and 20-year-aged SiR surfaces were shorter compared with those of Sample A (UV, Heating) and 10-year-aged SiR surfaces.
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Characterization of Surface Discharge Used for Measuring Degradation Degree of Polymer Insulator Reviewed
Khaing M.T., Miyake T., Sakoda T.
Proceedings of the IEEE International Conference on Properties and Applications of Dielectric Materials 254 - 257 2024.8
Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of the IEEE International Conference on Properties and Applications of Dielectric Materials
Polymer insulators with silicone rubber (SiR) insulation have unique properties and are installed all over the world. However, due to pollution deposits on the surface, the characteristics of polymer insulators become degraded. We have already investigated that the degradation degree of the polymer insulator can be evaluated by a 20-cycle salt-fog aging test or a surface discharge (SD) treatment. However, the decrease mechanism of the contact angle by such discharge treatment wasn't interpreted in detail. In this study, to characterize SD generated on the surfaces of SiR, we first measured the SD current. The observed maximum SD current did not significantly differ from that obtained during the 20-cycle-salt-fog aging test. In addition, the SD consisted of filamentary discharges. In measurements of optical emissions, emissions with wavelengths of less than 291 nm which can cut C-H bond of SiR weren't observed. Therefore, it is thought that the direct energy transfer from energetic particles with higher energy than the binding energy of C-H changes chemical characteristics and decreases the contact angle on the SiR surface.
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Partial Discharge Behavior Prior to Breakdown in Epoxy Resin Reviewed
Htet S.Z.L., Kondo T., Miyake T., Sakoda T., Nishimura T.
IEEJ Transactions on Electrical and Electronic Engineering 19 ( 12 ) 1927 - 1935 2024.7
Authorship：Corresponding author Publishing type：Research paper (scientific journal) Publisher：IEEJ Transactions on Electrical and Electronic Engineering
To evaluate the deterioration degree of insulation material by monitoring partial discharges (PDs), it is necessary to fully understand the PD behavior prior to breakdown. We performed measurements of temporal variations in the number and magnitude of PDs in a void of epoxy resin. It was found that the number of PDs with larger magnitude is less before breakdown and that there is a decreased tendency of the number and magnitude of PDs with the elapsed time. The tendency is remarkable as the applied electric field is small. Additionally, the time to breakdown becomes short when the scattering of the number of PDs per unit time decreases. © 2024 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC.
DOI： 10.1002/tee.24160
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Ko T.Z.W., Torihara R., Sakoda T., Hayashi N.
IEEJ Transactions on Electrical and Electronic Engineering 19 ( 6 ) 1105 - 1112 2024.6
Authorship：Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：IEEJ Transactions on Electrical and Electronic Engineering
Lightning surges are one of the major reasons of bypass diode (BPD) failure in photovoltaic modules. In this study, standard lightning impulse voltages (SLIVs) were directly applied to Schottky barrier diodes (SKB diodes) and rectifier diodes (PNJ diodes) with different electrical specifications. The critical voltages Vc of SLIV at which the diodes were damaged and the temporal variations of diode current (iD) and voltage (vD) were measured. It was found the iD-vD characteristics can be categorized into a total of eight patterns: four patterns for the forward SLIV application and the four for the reverse SLIV application, regardless of diode types. The measured results imply that the irreversible voltage dip that occurs before the termination of the reverse breakdown contributes significantly to diode damage in the both forward and reverse SLIV applications. SKB diodes exposed to the reverse SLIV are easily damaged at the lowest magnitude of SLIV among all combinations of diode types and SLIV directions. Once a diode has been damaged due to the first SLIV application, the second application of SLIV to the same diode causes remarkable change in the iD-vD characteristic even if the magnitude of the second SLIV is smaller than Vc. © 2024 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.
DOI： 10.1002/tee.24064
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Short-time Fabrication of Degraded Surface on Silicone Rubber Used for Insulators Reviewed
Khaing M.T., Yoshimura K., Miyake T., Sakoda T., Goto S., Anjiki T., Chiba T., Kasuga Y.
IEEE Transactions on Dielectrics and Electrical Insulation 31 ( 2 ) 1054 - 1061 2024.4
Publishing type：Research paper (scientific journal) Publisher：IEEE Transactions on Dielectrics and Electrical Insulation
Silicone rubber (SiR) insulators are degraded due to multiple stresses. To develop a degradation diagnostic technique, a lot of aged insulators are required. However, collecting a lot of several decades of used SiR insulators is difficult. Therefore, it is desired to fabricate the degraded SiR surface whose characteristics are similar to those of degraded SiR insulators in outdoor. To grasp characteristics of the degraded SiR surface, we first investigated characteristics of aged SiR insulators. Foreign matters on aged SiR specimens made the contact angle larger, and Si-O, Si-CH<sub>3</sub>, C-H, and O-H bonds decreased. Next, to fabricate the artificially degraded SiR surface, we proposed a 24 h – fabrication - cycle which consists of a red clay adhesion process, a UV irradiation process, a surface heating process, a heat radiation process, and a surface cleaning process. We evaluated effects of the UV irradiation and the surface heating, and then it was found that a combination of UV irradiation for breaking molecular structure and surface heating for promoting LMW dispersion played an important role in adhering red clay to SiR. The contact angle and the chemical structure on the artificially degraded SiR surface, which was fabricated by UV irradiation for 6 h and surface heating at 20°C or 40°C, were similar to those of a SiR specimen aged 10 years with the hydrophobicity of HC 2.
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Khaing M.T., Miyake T., Sakoda T., Kanenari U., Nishihiro Y.
Journal of Electrostatics 128 2024.3
Publishing type：Research paper (scientific journal) Publisher：Journal of Electrostatics
To establish an evaluation technique of the degradation degree of silicone rubber (SiR) surfaces, we first fabricated artificially degraded SiR surfaces. The fabrication process consisted of 5 steps and a 1-cycle test required 24 h. We fabricated the degraded SiR surfaces by a 1-cycle or a 2-cycle test. Next, the artificially degraded SiR surface was exposed to surface discharge (SD). The hydrophobicity recovery time on artificially degraded SiR surface increased with the increase in SD treatment time. It was found that the degradation degree of the SiR surface can be evaluated by hydrophobicity recovery time after SD treatment.
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Characteristics of Aged Silicone Rubber Insulators Used in Outdoor for 20 Years Reviewed
19 ( 4 ) 454 - 460 2024.1
Authorship：Last author Language：English Publishing type：Research paper (scientific journal)
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Degradation Monitoring of Silicone Rubber Used for Insulators Reviewed
May Thin Khaing, Kosei Yoshimura, Takuma Miyake, Tatsuya Sakoda, Shigehiko Goto, Tomikazu Anjiki, Tomoki Chiba, and Yasunori Kasuga
23rd Int. Symposium on High Voltage Engineering (ISH) 866 - 870 2023.8
Authorship：Last author Language：English Publishing type：Research paper (international conference proceedings)
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Formation of Degradation Layer on Silicone Rubber Used for Insulators Reviewed
Khaing M.T., Yoshimura K., Sakoda T., Goto S., Anjiki T., Chiba T., Kasuga Y.
2023 IEEE Electrical Insulation Conference, EIC 2023 2023.6
Language：English Publishing type：Research paper (international conference proceedings) Publisher：2023 IEEE Electrical Insulation Conference, EIC 2023
Silicone rubber (SiR) insulators have been increasingly used for transmission and distribution systems. However, it is concerned that performance and property of SiR insulator in operation are degraded due to multiple stresses. We now aim to develop a diagnosis technique of degradation degree of SiR insulator exposed to the multiple stresses. In order to investigate the degradation characteristics and establish the diagnosis technique, aged specimens are required. However, it is difficult to collect a lot of aged SiR insulators used for more than several decades. Therefore, we tried to fabricate the artificial degradation surface, which is similar to ones obtained from actual fields. To analyze the surface degradation of actually aged SiR insulators, hydrophobicity class (HC) of 22kV-SiR insulators arranged for 10 and 20 years in coastal areas was first evaluated. Next, considering the multiple stresses, the degradation surface was fabricated by red clay, UV ray irradiation and surface heating. Aged SiR specimens and artificially degraded SiR spmecimens were characterized by using a contact angle meter, a scanning electron microscopy (SEM), and an attenuated total reflectance-Fourier transform infrared spectrometer (ATR-FTIR). The hydrophobicity of artificially degraded SiR specimen can be decreased due to red clay adhesion/ surface pollution on its surface as the similar condition as actually aged SiR specimen. It was also found that Si-O bond, Si-CH3 bond and C-H bond can be controlled by UV irradiation and the heating temperature.
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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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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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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)