研究者詳細 - 小迫　雅裕

論文 - 小迫　雅裕

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Effect of Changes in Partial Discharge Activity on Resin Erosion in Simulated Voids 査読有り国際誌

Aoki Y., Takeuchi K., Kozako M., Hikita M., Ito D., Oyama K., Nakamae T., Maeda T., Ozaki T.

2024 10th International Conference on Condition Monitoring and Diagnosis Cmd 2024 ( 427 ) 525 - 528 2024年10月

担当区分：責任著者記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）

Korea Gangwon-do, 2024年10月20日 - 2024年10月24日

Resin materials, widely used in insulating applications, are susceptible to partial discharge (PD) erosion. This degradation can result in insulation breakdown. Despite the recognized impact of PD on insulation materials, the detailed effects of varying discharge activity on resin erosion remain underexplored. To investigate the degradation of resin resulting from variations in the discharge activity caused by prolonged charging, an analysis was conducted on the resin surface structure within voids in response to changes in the discharge activity within the simulated voids. The V-Q Lissaj ous method was employed to measure the energy of the discharge inj ected into the voids. As the discharge energy increased with charging time, the discharge activity in the voids weakened, resulting in observable changes in the erosive structure of the resin surface. Prolonged exposure to discharge resulted in localized erosion growth, culminating in the formation of deep pore structures near the columnar structures within the eroded area of the polyethylene terephthalate (PET) owing to PD. The growth of these structures may be attributed to the variations in the crystallinity of the PET on the discharge eroded surface. The evolution of these degradation stages could be ascertained from the change in discharge energy per unit time, and the erosion depth per energy at each stage could be determined. This information can be used for a more accurate prediction of insulation lifetime. In PET, the phenomenon of increased PD resistance at PD eroded area was confirmed. This can lead to the selection and design of more resilient electrical insulation systems. The findings of this study can contribute to improving the reliability and safety of high-voltage equipment.

DOI： 10.23919/CMD62064.2024.10766243

Scopus

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Comparative Analysis between Measured and Simulated Pulse Voltage Distribution in Form Wound Stator Winding of Inverter-Fed Motors 査読有り国際誌

Miyazaki K., Nagatani Y., Kuno T., Hikita M., Kozako M., Iwanaga T., Zaizen K., Inoue Y., Yamada T., Okamoto T.

Annual Report Conference on Electrical Insulation and Dielectric Phenomena CEIDP ( 1A9 ) 2024年10月

担当区分：責任著者記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）

USA Auburn, AL, 2024年10月06日 - 2024年10月09日

This paper presents a simulation study of a pulse voltage distribution within the windings of a motor using a high-frequency (HF) equivalent circuit model. The simulation results are validated by comparison with measured data, aimed at enhancing insulation design technology for next-generation inverter-fed motors. The investigation focuses on pulse voltage propagation between each coil-to-ground and turn-to-turn in the initial winding, which is crucial for selecting the optimal insulation design for evaluation. The subject of this study is an inverter-fed three-phase induction motor with a rated output of 75 kW and a rated voltage of 3kV<inf>rms</inf>. The winding configuration consists of two parallel wound types with 10 turns and 16 windings per phase, featuring 4 poles. The impulse voltage used had a rise time of 250 ns, a pulse width of 50μs, and a voltage amplitude of 1000 V. An impulse voltage was applied from the beginning to the end of Phase U, and output waveforms at each measurement point were obtained. Additionally, the output voltage waveforms for each turn were simulated using the developed HF equivalent circuit model, implemented in LTspice® (Analog Devices), a transient phenomenon simulation software, and compared with the measured results. The simulated results show good agreement with the measured results. The maximum simulated voltages matched measured values within an error margin of less than 3.7% for coil-to-ground and 9.5% for turn-to-turn in the initial winding. The developed HF equivalent circuit model is validated as a useful tool for evaluating surge voltage impacts in the insulation design of stator windings.

DOI： 10.1109/CEIDP61745.2024.10907706

Scopus

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Effect of Electric Field on Conductivity of Palm Fatty Acid Ester 査読有り国際誌

Okamoto T., Suenaga S., Tsuchie M., Hikita M., Kozako M.

Annual Report Conference on Electrical Insulation and Dielectric Phenomena CEIDP ( 2B5 ) 2024年10月

担当区分：最終著者記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）

USA Auburn, AL 2024年10月06日 - 2024年10月09日

Biodegradable ester oils have emerged as an environmentally sustainable alternative to traditional mineral oils in various applications. New uses, particularly in converter transformers, energy storage systems, and HVDC transformers, are under continuous investigation. The electrical conductivity of insulating materials is a key parameter for these novel applications; however, limited research has been conducted on the conductivity of biodegradable ester oils in comparison to mineral oil. This study examines the influence of electric field strength on the conductivity σ of palm fatty acid esters (PFAE) under DC voltage application ranging from 10 to 3000 seconds, and compares the results with those of mineral oil. The experimental results indicated that σ of PFAE decreases over time under electric fields ranging from 100 V/mm to 1 kV/mm, but increases with time under fields exceeding 1 kV/mm. Notably, the conductivity in long-term measurements was lower than in short-term measurements. When comparing the conductivities of PFAE, mineral oil, and synthetic esters, PFAE exhibited the highest conductivity across both short- and long-term measurements and various electric field strengths. This difference is attributed to the lower kinematic viscosity of PFAE compared to mineral oils and synthetic esters. The significant effect of kinematic viscosity on the conductivity was observed among the ester oils, with the ratio of conductivities closely matching the ratio of their kinematic viscosities. Furthermore, a comparison between ester oil and mineral oil revealed a more than 100-fold difference in conductivity, primarily due to the effect of ionic carrier conduction in the presence or absence of polar groups. Additionally, the higher charge density in ester-based insulating oils compared to mineral oils was identified as a contributing factor to this disparity.

DOI： 10.1109/CEIDP61745.2024.10907387

Scopus

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Breakdown Strength Comparison of Several Fluorinated Liquids with Different Molecular Structures 査読有り国際誌

Suenaga S., Okamoto T., Tsuchie M., Hikita M., Kozako M.

Proceedings of the IEEE International Conference on Properties and Applications of Dielectric Materials ( 281 ) 258 - 261 2024年08月

担当区分：最終著者記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）

Thailand Phuket 2024年08月04日 - 2024年08月07日

Fluorinated liquids are used as refrigerants and cleaning agents in various electrical equipment due to their excellent thermal, chemical, and electrical properties. However, the dielectric/insulating properties and breakdown mechanism of fluorinated liquids have not yet been clarified. Therefore, the authors compared the relative permittivity, dissipation factor and breakdown voltage of five fluorinated liquids with different molecular structures: HFE-7100 (C<inf>4</inf>F<inf>9</inf>OCH<inf>3</inf>), HFE-356mmz ((CF<inf>3</inf>)<inf>2</inf>CHOCH<inf>3</inf>), HFE-356mec (CF<inf>3</inf>CHFCF<inf>2</inf>OCH<inf>3</inf>), HFC-43-10mee (CF3CHFCHFCF2CF3) and Hexafluorobenzene (C6F6). This paper will help to discuss the effect of different molecular structures on the insulating properties. The relative permittivity and dissipation factor was measured using a liquid electrode and an LCR meter at an applied voltage of 1 V AC, a frequency of 60 Hz, and room temperature. The highest relative permittivity for HFE-356mmz was about 48.1 and the lowest for Hexafluorobenzene was 1.98. Similarly, the highest dissipation factor for HFE-356mmz was 18.621 and the lowest dissipation factor for Hexafluorobenzene was 0.0096. The breakdown voltage (BDV) was boosted at AC 3 kV/s and 15 points were obtained for each sample at 1 mm and 2.5 mm gap. Hexafluorobenzene was found to have a higher BDV than the other samples. From these results, it was found that Hexafluorobenzene, which had a smaller relative permittivity, had a higher BDV. In addition, HFE-7100, HFE-356mmz, HFE-356mec, and HFC-43-10mee, it was considered that bubbles were generated in the samples by Electro Hydro Dynamics (EHD) generated during high voltage charging, and that these bubbles entered between the electrodes, causing the breakdown voltage to decrease.

DOI： 10.1109/ICPADM61663.2024.10750631

Scopus

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Breakdown Characteristics of Insulating Oil in Uniform to Non-uniform Electric Field under AC Voltage 査読有り国際誌

Yoshida S., Yamatake A., Kozako M., Hikita M.

Proceedings of the 2024 IEEE 5th International Conference on Dielectrics Icd 2024 ( 1C-01 ) 2024年06月

担当区分：責任著者記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）

France Toulouse, 2024年06月30日 - 2024年07月04日

It is imperative that insulation designers understand breakdown voltage (BDV). BDV of transformer oil are generally understood to follow stressed oil volume (SOV) theory. However, estimating more than 90% stressed oil volume in non-uniform electric fields in a transformer is extremely time consuming. Therefore, we propose a prediction formula that can estimate the BDV of insulating oil easily. In this study, the breakdown characteristics of insulating oil were investigated in a non-uniform electric field under AC voltage application. Experimental results were obtained with those several bare electrodes and oil gap lengths. As a result, it was derived that a prediction formula represented by √UE<inf>max</inf> =25.3d•0.28 in the mineral oil and ester oil. It was also confirmed that experimental results matched to the prediction curve and could easily estimate the breakdown voltage.

DOI： 10.1109/ICD59037.2024.10613251

Scopus

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Simultaneous Measurement of Space Charge Distribution and Partial Discharge by PEA Method 査読有り国際誌

Endo K., Kondo K., Kobayashi J., Miyake H., Tanaka Y., Kozako M., Hikita M.

Proceedings of the 2024 IEEE 5th International Conference on Dielectrics Icd 2024 ( 3C-18 ) 2024年06月

担当区分：責任著者記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）

France Toulouse 2024年06月30日 - 2024年07月04日

In order to improve the efficiency of inverter-driven motors, it is required to prevent partial discharge, and it has been pointed out that PDIV may be lowered during operation due to the space charge that accumulates in the insulation material used to coat the windings. However, there have been few experimental attempts to demonstrate this effect. Therefore, in this study, the effect of space charge accumulation in insulating materials on PD characteristics was verified by the pulsed electroacoustic (PEA) metho. As a result, it was clarified that the space charge accumulation influences PDIV degradation.

DOI： 10.1109/ICD59037.2024.10613200

Scopus

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Identification of Defect Type in an Aged 22 kV Cast Resin Transformer from Phase-Resolved PD Patterns 査読有り国際誌

Miyagawa M., Yao Y., Satake T., Kawano H., Hikita M., Kozako M., Harada Y., Takei K., Ikeda M., Miyazaki K., Futakawa K.

Proceedings of the 2024 IEEE 5th International Conference on Dielectrics Icd 2024 ( 2B-13 ) 2024年06月

担当区分：責任著者記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）

France Toulouse 2024年06月30日 - 2024年07月04日

This paper presents identification of defect type in the insulation system of an aged 22 kV cast resin transformer (CRTr) from comparing phase-resolved partial discharge (PRPD) patterns with those in different electrode systems simulating various kinds of defects. Quantitative analysis of the PRPD patterns was performed using a measure of the difference between the two probability distributions, called the Kullback-Leibler (KL) divergence. Comparison of PRPD patterns using KL divergence value (KL-D) suggested the possibility that a defect type in the aged 22 kV CRTr was attributed to inter-layer voids. Furthermore, even for the PRPD pattern of CRTr, which had little apparent change over time, the value of KL-D increased with increasing cumulative application time tc. As a result, it can be said that KL divergence is a useful index in comparing PRPD patterns quantitatively.

DOI： 10.1109/ICD59037.2024.10613342

Scopus

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Effect of Elastomer Blend on High Temperature Dielectric Properties of Polypropylene 査読有り国際誌

Kim H., Shinozaki K., Hikita M., Kozako M., Yu S.

Proceedings of the 2024 IEEE 5th International Conference on Dielectrics Icd 2024 ( 2A-21 ) 2024年06月

担当区分：責任著者記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）

France Toulouse 2024年06月30日 - 2024年07月04日

This paper presents investigation on dielectric properties of polypropylene (PP), binary blend (iPP/EOC=4.4:5.6), and ternary blend 1 (iPP/EOC/PPC=4:5:1), and ternary blend2 (iPP/EOC/PPC=3.6/4.6/1.8) at high temperatures up to 150°C. EOC and PPC stand for ethylene-octene copolymers and EPR dispersed in PP, respectively. The relative complex permittivity ϵ<inf>r</inf>∗ = ϵ<inf>r</inf>′ -jϵ<inf>r</inf>′′ and AC conductivity σ<inf>ac</inf> were measured in a temperature range from 30°C to 150°C at frequencies from 1 Hz to 10 kHz. Experimental results revealed that the real part ϵ<inf>r</inf>′ of the relative permittivity of all kinds of material decreased with increasing temperature, though pristine PP exhibited a smallest decrease in ϵ<inf>r</inf>′ with temperature. While the imaginary part ϵ<inf>r</inf>′′ exhibited a linear decrease with the frequency in the log vs log plot below 1 kHz and above 100°C for binary blend, ternary blend1 and 2. The results indicate that the EOC addition to PP is contributed to the increase in the complex permittivity. It was also found that σ<inf>ac</inf> of binary blend, ternary blend1, and 2 remained constant below 1 kHz and above 110°C, while σ<inf>ac</inf> of all the samples increased proportionally with frequency above 1 kHz. The calculated activation energies derived from the temperature dependence of the DC conductivity of binary blend, ternary blend 1, and ternary blend 2 were 0.602, 0.849, and 0.791 eV, respectively, with ternary blend 1 having the largest activation energy. Ternary blend 1 with the largest value was considered the most likely to inhibit carrier transport.

DOI： 10.1109/ICD59037.2024.10613350

Scopus

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Comparison of High Temperature Dielectric Properties between Epoxy Resins with Alicyclic and Bisphenol A 査読有り国際誌

Shinozaki K., Hikita M., Kozako M., Ueshima M.

Proceedings of the 2024 IEEE 5th International Conference on Dielectrics Icd 2024 ( 2A-18 ) 2024年06月

担当区分：責任著者記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）

France Toulouse 2024年06月30日 - 2024年07月04日

The purpose of this study is to elucidate the dielectric properties of alicyclic epoxy resins at elevated temperatures. Compared to common bisphenol A epoxy resins, alicyclic epoxy resins have a higher glass transition temperature and lower viscosity in the liquid state. Therefore, alicyclic epoxy resins are expected to exhibit good dielectric properties in high temperature environments. In this paper, we compare the dielectric properties of alicyclic epoxy resins and bisphenol A epoxy resins from room temperature to high temperature.

DOI： 10.1109/ICD59037.2024.10613347

Scopus

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Effect of electric field on conductivity of synthetic ester 査読有り国際誌

Rui Yu, Shanika Matharage, Daigo Okumura, Motoo Tsuchie, Masahiro Kozako, Masayuki Hikita, Zhongdong Wang

IET Conference Proceedings ( The Institution of Engineering and Technology ) 2023 ( 46 ) 68 - 72 2024年04月

Long-term AC partial discharge characteristics of a 22 kV cast resin transformer in accelerated tests 査読有り国際誌

Mizuki Miyagawa, Yuanhang Yao, Ryota Koresawa, Hideaki Kawano, Masayuki Hikita, Masahiro Kozako, Katsutoshi Takei, Teruo Shibata, Tamotsu Uzuki, Kazuhiro Futakawa

IET Conference Proceedings ( The Institution of Engineering and Technology ) 2023 ( 46 ) 1127 - 1131 2024年04月

Partial discharge characteristics to breakdown in cast resin transformer suffering lightning impulses to accelerate aging 査読有り国際誌

Yuanhang Yao, Mizuki Miyagawa, Ryota Koresawa, Masahiro Kozako, Masayuki Hikita, Katsutoshi Takei, Teruo Shibata, Tamotsu Uzuki, Kazuhiro Futakawa

IET Conference Proceedings ( The Institution of Engineering and Technology ) 2023 ( 46 ) 538 - 542 2024年04月

Application of power line communication for online partial discharge monitoring in a simulated substation 査読有り国際誌

Lunnetta Safura Lumba, Akito Houdai, Masahiro Kozako, Masayuki Hikita, Hidefumi Sato, Masahiro Soeda

IET Conference Proceedings ( The Institution of Engineering and Technology ) 2023 ( 46 ) 482 - 487 2024年04月

Impedance Frequency Analysis of Stator Winding of Electric Motors using Highfrequency Equivalent Circuit 査読有り

K.Miyazaki, T.Kuno, M.Hikita, M.Kozako, T.Okamoto, Y.Inoue, K.Zaizen, T.Yamada, T.Iwanaga

2023 IEEE Conference on Electrical Insulation and Dielectric Phenomena(CEIDP) ( 2B9 ) 383 - 386 2023年10月

Improvement of Partial Discharge Signal Recognition for Power Cable Lines 査読有り国際誌

M.Chen, M.Kozako, M.Hikita, N.Takeuchi, Z.Zhou, J.Lu

2023 International Symposium on Electrical Insulating Materials (ISEIM) ( A-1 ) 2023年09月

Digest Report of Cooperative Research Committee on EINA Magazine 査読有り国際誌

Y.Tanaka, M.Kozako, N.Fuse

2023 International Symposium on Electrical Insulating Materials (ISEIM) ( DR-1 ) 2023年09月

Effect of Moisture Content on Temperature Dependence of Partial Discharge Characteristics of Biodegradable Ester Oils 査読有り国際誌

T.Okamoto, D.Okumura, M.Tsuchie, M.Hikita, M.Kozako

2023 International Symposium on Electrical Insulating Materials (ISEIM) ( MVP4-6 ) 2023年09月

Effect of Carbon Black Addition on Dielectric Breakdown Strength of Alicyclic Epoxy Resins 査読有り国際誌

K.Shinozaki, D.Okumura, M.Hikita, M.Kozako

2023 International Symposium on Electrical Insulating Materials (ISEIM) ( MVP3-5 ) 2023年09月

LiquidLong-Term Partial Discharge Characteristics till Breakdown in a 22 kV Cast Resin Transformer 査読有り国際誌

M.Miyagawa, Y.Yao, R.Koresawa, H.Kawano, M.Hikita, M.Kozako

2023 International Symposium on Electrical Insulating Materials (ISEIM) ( MVP1-5 ) 2023年09月

Partial Discharge Detection and Analysis on a Cast Resin Transformer under Lightning Impulse Voltage 査読有り国際誌

Y.Yao, M.Miyagawa, R.Koresawa, M.Kozako, M.Hikita, K.Takei, T.Shibata, T.Uzuki, K.Futakawa, H.Ozeki

2023 International Symposium on Electrical Insulating Materials (ISEIM) ( F-4 ) 2023年09月

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