Masashi Natsui - Academia.edu (original) (raw)

Papers by Masashi Natsui

IEEE Transactions on Electromagnetic Compatibility, Feb 1, 2021

In this article, lightning-induced overvoltages due to inclined lightning are investigated by a f... more In this article, lightning-induced overvoltages due to inclined lightning are investigated by a finite-difference time-domain (FDTD) method for distribution lines of a single conductor and a multiphase line (three-phase conductors with a shield wire, utility poles, groundings, and arresters). The FDTD model is validated in comparison with results of circuit-theory-based analytical and numerical calculation methods. In the single conductor line, the influences of inclined lightning on the induced voltage waveform, peak voltage, and voltage profile along the line are investigated with several combinations of lightning distances, earth resistivities, and lightning current waveforms. The induced voltage is significantly influenced by the lightning inclination toward the line (angle θ). The increased ratio of the peak voltage by the angle θ becomes larger with lower earth resistivity and shorter rise time of the lightning current. While the inclination along the line (angle ϕ) makes only minor differences on the peak voltage, the voltage profile along the line becomes asymmetric. In the multiphase line, the influence of the angle θ on the voltage becomes similar to that in the single conductor line. These results clearly indicate that the lightning inclination should be considered for an accurate evaluation of lightning-induced voltages.

I am sincerely grateful to Prof. Akihiro Ametani for his outstanding motivation, great patience, ... more I am sincerely grateful to Prof. Akihiro Ametani for his outstanding motivation, great patience, and continuous encouragement throughout my study. His advice with deep insight and comprehensive knowledge were very helpful in all aspects of my research work. Discussion and assistance provided by Prof. Ilhan Kocar were much appreciated. All colleagues at the department for their friendship and support, Isabel Lafaia, Baki Cetindag,

IEEE Transactions on Electromagnetic Compatibility, Oct 1, 2020

This article investigates the transient characteristics of earth currents and grounding potential... more This article investigates the transient characteristics of earth currents and grounding potential rises (GPRs) produced by lightning strikes directly to the earth and to a vertical conductor with a grounding electrode. Influences of the earth depth and the distance from the lightning channel are discussed based on a field test and finite-difference time-domain (FDTD) computed results. The validity of the FDTD is confirmed in comparison with the field test results. Based on the FDTD results, a large portion of the lightning current is observed to flow along the earth surface during a transient period. The current density is roughly proportional to 1/r 2 (r: distance from the lightning base) for the lightning to the earth surface, and 1/Lr for the lightning to a vertical conductor with a grounding electrode of length L. The GPR shows similar characteristics. Electromagnetic field radiated from the lightning to the earth contributes to the peak of the earth-surface current, and it becomes dominant when r is larger than 10 m. The pole grounding of a distribution line nearby the lightning absorbs a portion of the lightning current and, thus, the current density becomes larger toward the distribution pole.

Electric Power Systems Research, Jul 1, 2018

This paper investigates lightning induced voltages on a distribution line, when the lightning cha... more This paper investigates lightning induced voltages on a distribution line, when the lightning channel is not vertical but angled to the line and the earth representation is based on the finite-difference time-domain (FDTD) method. The effect of the current flowing into the earth, after the lightning channel touches the earth, is also investigated. The induced voltages are quite dependent on the angle of the channel to the line as can be easily estimated. It is found that the lightning angle with the line causes significant increase of the voltage and the effect of the earth resistivity on the induced voltage has been made clear when considering the inclined channel. Since the induced voltage is, in theory, proportional to the frequency of the inducing current, i.e. inversely proportional to rise time Tf when the inducing and induced circuits are parallel. When the lightning channel is angled, the proportional relation is less clear than that in the vertical channel. This fact has to be taken into account when discussing the effect of Tf. The current flowing in the earth is also affected by the lightning inclination and the voltage drop along the earth surface due to the current becomes larger than that in the vertical lightning case.

Electrical Engineering in Japan, Jul 19, 2010

More and more electronics are intended for use in adverse environments at high temperatures with ... more More and more electronics are intended for use in adverse environments at high temperatures with high humidity. The spatial distributions of internal charge carriers, mainly due to ionic impurities that appear in hot and humid environments, are considered to affect the reliability of bulk insulation. Therefore, the authors examined space charge behavior inside paper/phenol‐resin composites for printed circuit boards under DC voltages, focusing on the effect of the water absorption temperature. Both the sample weight and thickness were increased monotonically by immersion in water with an increase in the water temperature from 24 to 85 , indicating that the water absorption by the sample was temperature dependent. In the early periods of water absorption (up to 10 hours), the electric field decreased near the two electrodes and increased in the other regions. Furthermore, heterocharge formation was observed near the cathode as the water absorption progressed, becoming more significant at higher water temperatures. Ion chromatography analyses detected numerous ions such as Na+, NH4+NH_{4}^{+}NH4+ and Cl‐ from the water, in which the sample had been immersed for 100 hours at various temperatures. It is highly possible that these ions are responsible for the heterocharge formation. 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 173(2): 1–7, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20992

Electric Power Systems Research, Dec 1, 2020

This paper investigates lightning induced surges on an overhead line considering "bent" and "comp... more This paper investigates lightning induced surges on an overhead line considering "bent" and "computationallygenerated" non-vertical lightning channels by using a finitedifference time-domain (FDTD) method. In the bent lightning study, the channel is represented by combinations of vertical and inclined paths with different connecting (bent) heights. It is found that the lightning channel geometry under 100-m altitude is significant for the peak voltage when severe conditions of a 1/200μs current and a lightning distance of 50 m are assumed. A lightning-like (zig-zag) channel is computationally generated by a probabilistic calculation based on an electric potential distribution in a three-dimensional space, and its induced voltage is compared with that by a simply-inclined channel. When the inclinations are set to the average angles (θ and φ) under 100 m in the computed channel, the induced voltages show good agreement. The difference is less than 10 % and it decreases with higher earth resistivity. These results indicate that realistic non-vertical lightning can be represented by simply-inclined lightning by considering average inclined angles in low altitude.

The transactions of the Institute of Electrical Engineers of Japan.A, 2011

ABSTRACT

Pulsed electroacoustic (PEA) method is applied as a nondestructive technique to detect ion migrat... more Pulsed electroacoustic (PEA) method is applied as a nondestructive technique to detect ion migration that progresses to the thickness direction in insulation composites for printed circuit boards. In both cases of a paper/phenol-resin composite and a glass/epoxy-resin composite, penetration of Cu migration into the bulk after aging was confirmed. Namely, a shift of the peak location of positive charge, which corresponds to the progress of migration in the aged composite, is observable by the PEA method.

IEEE Transactions on Electromagnetic Compatibility, Feb 1, 2020

This paper investigates lightning surges on a distribution line reported using a finite-differenc... more This paper investigates lightning surges on a distribution line reported using a finite-difference time-domain (FDTD) method. FDTD simulation results show a satisfactory agreement with measured lightning currents when lightning strikes ground nearby a distribution line. The current and voltage characteristics along the line, which were not measured in the test, are calculated by the FDTD simulation. Parametric analysis shows that lightning currents and voltages are dependent on the lightning position, distance from the lightning to the nearest pole, and pole grounding resistance. A large portion of phase-wire voltage is induced by the lightning channel current, and correspondingly, a large portion of phase-wire current is produced by the induced voltage. When the lightning channel is inclined, the peak current and voltage vary by +10% to 10% depending on the inclined angle. The effect of neutral wire position in the line is also investigated, and the induced voltage at the nearest pole to the lightning can be effectively suppressed by installing two neutral wires above and under the phase wires. EMTP simulation results agree qualitatively well with the measurement and FDTD results.

Electric Power Systems Research, Jul 1, 2018

This paper is focused on the oscillating frequencies of very-fast transients (VFTs) generated by ... more This paper is focused on the oscillating frequencies of very-fast transients (VFTs) generated by disconnector and circuit breaker operations in gas-insulated substations (GISs) related to electromagnetic disturbances (EMDs). Test results of the VFT amplitudes and oscillating frequencies are summarized, and the measured results have shown that there is no significant difference of the frequencies in the high-voltage main circuits and the low-voltage control circuits in the GISs. Modeling of GIS elements for VFT simulations by EMT-type software are explained, and simulation examples are demonstrated in comparison with test results. Also, FDTD (finite-difference timedomain) computations are performed, and the calculated results are compared with EMTP simulation results. If proper modeling is adopted, EMTP and FDTD results show a reasonable agreement.

2021 IEEE Power & Energy Society General Meeting (PESGM), Jul 26, 2021

In this article, lightning-induced overvoltages due to inclined lightning are investigated by a f... more In this article, lightning-induced overvoltages due to inclined lightning are investigated by a finite-difference time-domain (FDTD) method for distribution lines of a single conductor and a multiphase line (three-phase conductors with a shield wire, utility poles, groundings, and arresters). The FDTD model is validated in comparison with results of circuit-theory-based analytical and numerical calculation methods. In the single conductor line, the influences of inclined lightning on the induced voltage waveform, peak voltage, and voltage profile along the line are investigated with several combinations of lightning distances, earth resistivities, and lightning current waveforms. The induced voltage is significantly influenced by the lightning inclination toward the line (angle θ). The increased ratio of the peak voltage by the angle θ becomes larger with lower earth resistivity and shorter rise time of the lightning current. While the inclination along the line (angle ϕ) makes only minor differences on the peak voltage, the voltage profile along the line becomes asymmetric. In the multiphase line, the influence of the angle θ on the voltage becomes similar to that in the single conductor line. These results clearly indicate that the lightning inclination should be considered for an accurate evaluation of lightning-induced voltages.

2009 IEEE Conference on Electrical Insulation and Dielectric Phenomena, 2009

Pulsed electroacoustic (PEA) method was applied as a nondestructive method to detect electrochemi... more Pulsed electroacoustic (PEA) method was applied as a nondestructive method to detect electrochemical migration in a sheet of epoxy resin and a sheet of laminate consisting of the same resin and a paper/phenol-resin composite. A significant decrease in the amount of negative charge was observed at the interface between the resin and the composite when the sample was the laminate. This is assumed to be due to the progress of electrochemical migration in the thickness direction. On the other hand, such a change in charge density was hardly observed when the sample was a sheet of epoxy resin. The electric field intensity in the epoxy resin layer in the laminate is assumed to be significantly enhanced, since the resistivity is much higher in the epoxy resin than in the composite. This seems to be the main reason why the electrochemical migration was induced only in the epoxy layer in the laminate. This means that observation of electrochemical migration in epoxy resin by the PEA method b...

RESUME Les surtensions induites par la foudre deviennent un sujet important dans le domaine des r... more RESUME Les surtensions induites par la foudre deviennent un sujet important dans le domaine des reseaux de distribution. Une evaluation precise des tensions induites est tres essentielle pour la protection contre la foudre. Un probleme des evaluations existantes est qu'un canal de foudre vertical et une terre parfaitement conductrice, qui ne sont pas realistes, sont supposes dans la plupart des cas. Ces hypotheses necessitent des recherches plus approfondies pour une evaluation precise de la tension induite. L'objectif principal de cette these est de reveler et resumer (1) les influences de la foudre non verticale sur les surtensions induites par la foudre dans les reseaux de distribution et (2) le comportement du courant de foudre dans une terre avec pertes, pour une evaluation precise des tensions induites. Pour (1), les circuits du modele FDTD pour representer la foudre non verticale sont construits et les influences de la foudre non verticale sur les tensions induites so...

In this article, lightning-induced overvoltages due to inclined lightning are investigated by a f... more In this article, lightning-induced overvoltages due to inclined lightning are investigated by a finite-difference time-domain (FDTD) method for distribution lines of a single conductor and a multiphase line (three-phase conductors with a shield wire, utility poles, groundings, and arresters). The FDTD model is validated in comparison with results of circuit-theory-based analytical and numerical calculation methods. In the single conductor line, the influences of inclined lightning on the induced voltage waveform, peak voltage, and voltage profile along the line are investigated with several combinations of lightning distances, earth resistivities, and lightning current waveforms. The induced voltage is significantly influenced by the lightning inclination toward the line (angle θ). The increased ratio of the peak voltage by the angle θ becomes larger with lower earth resistivity and shorter rise time of the lightning current. While the inclination along the line (angle ϕ) makes only...

Electric Power Systems Research, 2020

This paper investigates lightning induced over-voltages on overhead lines considering “bent” and ... more This paper investigates lightning induced over-voltages on overhead lines considering “bent” and “computationally-generated” non-vertical lightning channels by using a finite-difference time-domain (FDTD) method. In the former case, combinations of vertical and inclined channels with different connecting heights are modeled to represent “bent” lightning. It is made clear that the peak voltage is significantly influenced by the lightning channel geometry under 100-m altitude when severe conditions of a 1/200-μs current and a lightning distance of 50 m are assumed. Induced voltages on the three-phase line show similar characteristics to those on the single conductor line. In the latter case, a lightning-like (zig-zag) channel is computationally generated by a probabilistic calculation based on an electric potential distribution in a three-dimensional space, and its induced voltage is compared with that by a simply-inclined channel. When average inclined angles under 100-m altitude in ...

In order to study the growth of electrochemical migration along the thickness direction, paper/ph... more In order to study the growth of electrochemical migration along the thickness direction, paper/phenol-resin composite on printed wiring boards was aged at 85 °C and 85 %RH by applying of a dc voltage. Then, the sample was observed by a scanning electron microscope with a function of energy dispersive spectroscopy (SEM-EDS) analysis. Space charge distributions in the sample were also measured by the pulsed electroacoustic method. Signals of SEM-EDS showing the presence of Cu were observed on both the anode and cathode. This fact indicates that ionized copper moves toward the cathode inside the composite when an electric field is applied at high temperatures in a highly humid atmosphere.

IEEE Transactions on Electromagnetic Compatibility

This article investigates the transient characteristics of earth currents and grounding potential... more This article investigates the transient characteristics of earth currents and grounding potential rises (GPRs) produced by lightning strikes directly to the earth and to a vertical conductor with a grounding electrode. Influences of the earth depth and the distance from the lightning channel are discussed based on a field test and finite-difference time-domain (FDTD) computed results. The validity of the FDTD is confirmed in comparison with the field test results. Based on the FDTD results, a large portion of the lightning current is observed to flow along the earth surface during a transient period. The current density is roughly proportional to 1/r2 (r: distance from the lightning base) for the lightning to the earth surface, and 1/Lr for the lightning to a vertical conductor with a grounding electrode of length L. The GPR shows similar characteristics. Electromagnetic field radiated from the lightning to the earth contributes to the peak of the earth-surface current, and it becomes dominant when r is larger than 10 m. The pole grounding of a distribution line nearby the lightning absorbs a portion of the lightning current and, thus, the current density becomes larger toward the distribution pole.

Electric Power Systems Research

This paper investigates lightning induced voltages on a distribution line, when the lightning cha... more This paper investigates lightning induced voltages on a distribution line, when the lightning channel is not vertical but angled to the line and the earth representation is based on the finite-difference time-domain (FDTD) method. The effect of the current flowing into the earth, after the lightning channel touches the earth, is also investigated. The induced voltages are quite dependent on the angle of the channel to the line as can be easily estimated. It is found that the lightning angle with the line causes significant increase of the voltage and the effect of the earth resistivity on the induced voltage has been made clear when considering the inclined channel. Since the induced voltage is, in theory, proportional to the frequency of the inducing current, i.e. inversely proportional to rise time Tf when the inducing and induced circuits are parallel. When the lightning channel is angled, the proportional relation is less clear than that in the vertical channel. This fact has to be taken into account when discussing the effect of Tf. The current flowing in the earth is also affected by the lightning inclination and the voltage drop along the earth surface due to the current becomes larger than that in the vertical lightning case.

Electric Power Systems Research

This paper is focused on the oscillating frequencies of very-fast transients (VFTs) generated by ... more This paper is focused on the oscillating frequencies of very-fast transients (VFTs) generated by disconnector and circuit breaker operations in gas-insulated substations (GISs) related to electromagnetic disturbances (EMDs). Test results of the VFT amplitudes and oscillating frequencies are summarized, and the measured results have shown that there is no significant difference of the frequencies in the high-voltage main circuits and the low-voltage control circuits in the GISs. Modeling of GIS elements for VFT simulations by EMT-type software are explained, and simulation examples are demonstrated in comparison with test results. Also, FDTD (finite-difference timedomain) computations are performed, and the calculated results are compared with EMTP simulation results. If proper modeling is adopted, EMTP and FDTD results show a reasonable agreement.

IEEE Transactions on Electromagnetic Compatibility, Feb 1, 2021

In this article, lightning-induced overvoltages due to inclined lightning are investigated by a f... more In this article, lightning-induced overvoltages due to inclined lightning are investigated by a finite-difference time-domain (FDTD) method for distribution lines of a single conductor and a multiphase line (three-phase conductors with a shield wire, utility poles, groundings, and arresters). The FDTD model is validated in comparison with results of circuit-theory-based analytical and numerical calculation methods. In the single conductor line, the influences of inclined lightning on the induced voltage waveform, peak voltage, and voltage profile along the line are investigated with several combinations of lightning distances, earth resistivities, and lightning current waveforms. The induced voltage is significantly influenced by the lightning inclination toward the line (angle θ). The increased ratio of the peak voltage by the angle θ becomes larger with lower earth resistivity and shorter rise time of the lightning current. While the inclination along the line (angle ϕ) makes only minor differences on the peak voltage, the voltage profile along the line becomes asymmetric. In the multiphase line, the influence of the angle θ on the voltage becomes similar to that in the single conductor line. These results clearly indicate that the lightning inclination should be considered for an accurate evaluation of lightning-induced voltages.

I am sincerely grateful to Prof. Akihiro Ametani for his outstanding motivation, great patience, ... more I am sincerely grateful to Prof. Akihiro Ametani for his outstanding motivation, great patience, and continuous encouragement throughout my study. His advice with deep insight and comprehensive knowledge were very helpful in all aspects of my research work. Discussion and assistance provided by Prof. Ilhan Kocar were much appreciated. All colleagues at the department for their friendship and support, Isabel Lafaia, Baki Cetindag,

IEEE Transactions on Electromagnetic Compatibility, Oct 1, 2020

This article investigates the transient characteristics of earth currents and grounding potential... more This article investigates the transient characteristics of earth currents and grounding potential rises (GPRs) produced by lightning strikes directly to the earth and to a vertical conductor with a grounding electrode. Influences of the earth depth and the distance from the lightning channel are discussed based on a field test and finite-difference time-domain (FDTD) computed results. The validity of the FDTD is confirmed in comparison with the field test results. Based on the FDTD results, a large portion of the lightning current is observed to flow along the earth surface during a transient period. The current density is roughly proportional to 1/r 2 (r: distance from the lightning base) for the lightning to the earth surface, and 1/Lr for the lightning to a vertical conductor with a grounding electrode of length L. The GPR shows similar characteristics. Electromagnetic field radiated from the lightning to the earth contributes to the peak of the earth-surface current, and it becomes dominant when r is larger than 10 m. The pole grounding of a distribution line nearby the lightning absorbs a portion of the lightning current and, thus, the current density becomes larger toward the distribution pole.

Electric Power Systems Research, Jul 1, 2018

This paper investigates lightning induced voltages on a distribution line, when the lightning cha... more This paper investigates lightning induced voltages on a distribution line, when the lightning channel is not vertical but angled to the line and the earth representation is based on the finite-difference time-domain (FDTD) method. The effect of the current flowing into the earth, after the lightning channel touches the earth, is also investigated. The induced voltages are quite dependent on the angle of the channel to the line as can be easily estimated. It is found that the lightning angle with the line causes significant increase of the voltage and the effect of the earth resistivity on the induced voltage has been made clear when considering the inclined channel. Since the induced voltage is, in theory, proportional to the frequency of the inducing current, i.e. inversely proportional to rise time Tf when the inducing and induced circuits are parallel. When the lightning channel is angled, the proportional relation is less clear than that in the vertical channel. This fact has to be taken into account when discussing the effect of Tf. The current flowing in the earth is also affected by the lightning inclination and the voltage drop along the earth surface due to the current becomes larger than that in the vertical lightning case.

Electrical Engineering in Japan, Jul 19, 2010

More and more electronics are intended for use in adverse environments at high temperatures with ... more More and more electronics are intended for use in adverse environments at high temperatures with high humidity. The spatial distributions of internal charge carriers, mainly due to ionic impurities that appear in hot and humid environments, are considered to affect the reliability of bulk insulation. Therefore, the authors examined space charge behavior inside paper/phenol‐resin composites for printed circuit boards under DC voltages, focusing on the effect of the water absorption temperature. Both the sample weight and thickness were increased monotonically by immersion in water with an increase in the water temperature from 24 to 85 , indicating that the water absorption by the sample was temperature dependent. In the early periods of water absorption (up to 10 hours), the electric field decreased near the two electrodes and increased in the other regions. Furthermore, heterocharge formation was observed near the cathode as the water absorption progressed, becoming more significant at higher water temperatures. Ion chromatography analyses detected numerous ions such as Na+, NH4+NH_{4}^{+}NH4+ and Cl‐ from the water, in which the sample had been immersed for 100 hours at various temperatures. It is highly possible that these ions are responsible for the heterocharge formation. 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 173(2): 1–7, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20992

Electric Power Systems Research, Dec 1, 2020

This paper investigates lightning induced surges on an overhead line considering "bent" and "comp... more This paper investigates lightning induced surges on an overhead line considering "bent" and "computationallygenerated" non-vertical lightning channels by using a finitedifference time-domain (FDTD) method. In the bent lightning study, the channel is represented by combinations of vertical and inclined paths with different connecting (bent) heights. It is found that the lightning channel geometry under 100-m altitude is significant for the peak voltage when severe conditions of a 1/200μs current and a lightning distance of 50 m are assumed. A lightning-like (zig-zag) channel is computationally generated by a probabilistic calculation based on an electric potential distribution in a three-dimensional space, and its induced voltage is compared with that by a simply-inclined channel. When the inclinations are set to the average angles (θ and φ) under 100 m in the computed channel, the induced voltages show good agreement. The difference is less than 10 % and it decreases with higher earth resistivity. These results indicate that realistic non-vertical lightning can be represented by simply-inclined lightning by considering average inclined angles in low altitude.

The transactions of the Institute of Electrical Engineers of Japan.A, 2011

ABSTRACT

Pulsed electroacoustic (PEA) method is applied as a nondestructive technique to detect ion migrat... more Pulsed electroacoustic (PEA) method is applied as a nondestructive technique to detect ion migration that progresses to the thickness direction in insulation composites for printed circuit boards. In both cases of a paper/phenol-resin composite and a glass/epoxy-resin composite, penetration of Cu migration into the bulk after aging was confirmed. Namely, a shift of the peak location of positive charge, which corresponds to the progress of migration in the aged composite, is observable by the PEA method.

IEEE Transactions on Electromagnetic Compatibility, Feb 1, 2020

This paper investigates lightning surges on a distribution line reported using a finite-differenc... more This paper investigates lightning surges on a distribution line reported using a finite-difference time-domain (FDTD) method. FDTD simulation results show a satisfactory agreement with measured lightning currents when lightning strikes ground nearby a distribution line. The current and voltage characteristics along the line, which were not measured in the test, are calculated by the FDTD simulation. Parametric analysis shows that lightning currents and voltages are dependent on the lightning position, distance from the lightning to the nearest pole, and pole grounding resistance. A large portion of phase-wire voltage is induced by the lightning channel current, and correspondingly, a large portion of phase-wire current is produced by the induced voltage. When the lightning channel is inclined, the peak current and voltage vary by +10% to 10% depending on the inclined angle. The effect of neutral wire position in the line is also investigated, and the induced voltage at the nearest pole to the lightning can be effectively suppressed by installing two neutral wires above and under the phase wires. EMTP simulation results agree qualitatively well with the measurement and FDTD results.

Electric Power Systems Research, Jul 1, 2018

This paper is focused on the oscillating frequencies of very-fast transients (VFTs) generated by ... more This paper is focused on the oscillating frequencies of very-fast transients (VFTs) generated by disconnector and circuit breaker operations in gas-insulated substations (GISs) related to electromagnetic disturbances (EMDs). Test results of the VFT amplitudes and oscillating frequencies are summarized, and the measured results have shown that there is no significant difference of the frequencies in the high-voltage main circuits and the low-voltage control circuits in the GISs. Modeling of GIS elements for VFT simulations by EMT-type software are explained, and simulation examples are demonstrated in comparison with test results. Also, FDTD (finite-difference timedomain) computations are performed, and the calculated results are compared with EMTP simulation results. If proper modeling is adopted, EMTP and FDTD results show a reasonable agreement.

2021 IEEE Power & Energy Society General Meeting (PESGM), Jul 26, 2021

In this article, lightning-induced overvoltages due to inclined lightning are investigated by a f... more In this article, lightning-induced overvoltages due to inclined lightning are investigated by a finite-difference time-domain (FDTD) method for distribution lines of a single conductor and a multiphase line (three-phase conductors with a shield wire, utility poles, groundings, and arresters). The FDTD model is validated in comparison with results of circuit-theory-based analytical and numerical calculation methods. In the single conductor line, the influences of inclined lightning on the induced voltage waveform, peak voltage, and voltage profile along the line are investigated with several combinations of lightning distances, earth resistivities, and lightning current waveforms. The induced voltage is significantly influenced by the lightning inclination toward the line (angle θ). The increased ratio of the peak voltage by the angle θ becomes larger with lower earth resistivity and shorter rise time of the lightning current. While the inclination along the line (angle ϕ) makes only minor differences on the peak voltage, the voltage profile along the line becomes asymmetric. In the multiphase line, the influence of the angle θ on the voltage becomes similar to that in the single conductor line. These results clearly indicate that the lightning inclination should be considered for an accurate evaluation of lightning-induced voltages.

2009 IEEE Conference on Electrical Insulation and Dielectric Phenomena, 2009

Pulsed electroacoustic (PEA) method was applied as a nondestructive method to detect electrochemi... more Pulsed electroacoustic (PEA) method was applied as a nondestructive method to detect electrochemical migration in a sheet of epoxy resin and a sheet of laminate consisting of the same resin and a paper/phenol-resin composite. A significant decrease in the amount of negative charge was observed at the interface between the resin and the composite when the sample was the laminate. This is assumed to be due to the progress of electrochemical migration in the thickness direction. On the other hand, such a change in charge density was hardly observed when the sample was a sheet of epoxy resin. The electric field intensity in the epoxy resin layer in the laminate is assumed to be significantly enhanced, since the resistivity is much higher in the epoxy resin than in the composite. This seems to be the main reason why the electrochemical migration was induced only in the epoxy layer in the laminate. This means that observation of electrochemical migration in epoxy resin by the PEA method b...

RESUME Les surtensions induites par la foudre deviennent un sujet important dans le domaine des r... more RESUME Les surtensions induites par la foudre deviennent un sujet important dans le domaine des reseaux de distribution. Une evaluation precise des tensions induites est tres essentielle pour la protection contre la foudre. Un probleme des evaluations existantes est qu'un canal de foudre vertical et une terre parfaitement conductrice, qui ne sont pas realistes, sont supposes dans la plupart des cas. Ces hypotheses necessitent des recherches plus approfondies pour une evaluation precise de la tension induite. L'objectif principal de cette these est de reveler et resumer (1) les influences de la foudre non verticale sur les surtensions induites par la foudre dans les reseaux de distribution et (2) le comportement du courant de foudre dans une terre avec pertes, pour une evaluation precise des tensions induites. Pour (1), les circuits du modele FDTD pour representer la foudre non verticale sont construits et les influences de la foudre non verticale sur les tensions induites so...

In this article, lightning-induced overvoltages due to inclined lightning are investigated by a f... more In this article, lightning-induced overvoltages due to inclined lightning are investigated by a finite-difference time-domain (FDTD) method for distribution lines of a single conductor and a multiphase line (three-phase conductors with a shield wire, utility poles, groundings, and arresters). The FDTD model is validated in comparison with results of circuit-theory-based analytical and numerical calculation methods. In the single conductor line, the influences of inclined lightning on the induced voltage waveform, peak voltage, and voltage profile along the line are investigated with several combinations of lightning distances, earth resistivities, and lightning current waveforms. The induced voltage is significantly influenced by the lightning inclination toward the line (angle θ). The increased ratio of the peak voltage by the angle θ becomes larger with lower earth resistivity and shorter rise time of the lightning current. While the inclination along the line (angle ϕ) makes only...

Electric Power Systems Research, 2020

This paper investigates lightning induced over-voltages on overhead lines considering “bent” and ... more This paper investigates lightning induced over-voltages on overhead lines considering “bent” and “computationally-generated” non-vertical lightning channels by using a finite-difference time-domain (FDTD) method. In the former case, combinations of vertical and inclined channels with different connecting heights are modeled to represent “bent” lightning. It is made clear that the peak voltage is significantly influenced by the lightning channel geometry under 100-m altitude when severe conditions of a 1/200-μs current and a lightning distance of 50 m are assumed. Induced voltages on the three-phase line show similar characteristics to those on the single conductor line. In the latter case, a lightning-like (zig-zag) channel is computationally generated by a probabilistic calculation based on an electric potential distribution in a three-dimensional space, and its induced voltage is compared with that by a simply-inclined channel. When average inclined angles under 100-m altitude in ...

In order to study the growth of electrochemical migration along the thickness direction, paper/ph... more In order to study the growth of electrochemical migration along the thickness direction, paper/phenol-resin composite on printed wiring boards was aged at 85 °C and 85 %RH by applying of a dc voltage. Then, the sample was observed by a scanning electron microscope with a function of energy dispersive spectroscopy (SEM-EDS) analysis. Space charge distributions in the sample were also measured by the pulsed electroacoustic method. Signals of SEM-EDS showing the presence of Cu were observed on both the anode and cathode. This fact indicates that ionized copper moves toward the cathode inside the composite when an electric field is applied at high temperatures in a highly humid atmosphere.

IEEE Transactions on Electromagnetic Compatibility

This article investigates the transient characteristics of earth currents and grounding potential... more This article investigates the transient characteristics of earth currents and grounding potential rises (GPRs) produced by lightning strikes directly to the earth and to a vertical conductor with a grounding electrode. Influences of the earth depth and the distance from the lightning channel are discussed based on a field test and finite-difference time-domain (FDTD) computed results. The validity of the FDTD is confirmed in comparison with the field test results. Based on the FDTD results, a large portion of the lightning current is observed to flow along the earth surface during a transient period. The current density is roughly proportional to 1/r2 (r: distance from the lightning base) for the lightning to the earth surface, and 1/Lr for the lightning to a vertical conductor with a grounding electrode of length L. The GPR shows similar characteristics. Electromagnetic field radiated from the lightning to the earth contributes to the peak of the earth-surface current, and it becomes dominant when r is larger than 10 m. The pole grounding of a distribution line nearby the lightning absorbs a portion of the lightning current and, thus, the current density becomes larger toward the distribution pole.

Electric Power Systems Research

This paper investigates lightning induced voltages on a distribution line, when the lightning cha... more This paper investigates lightning induced voltages on a distribution line, when the lightning channel is not vertical but angled to the line and the earth representation is based on the finite-difference time-domain (FDTD) method. The effect of the current flowing into the earth, after the lightning channel touches the earth, is also investigated. The induced voltages are quite dependent on the angle of the channel to the line as can be easily estimated. It is found that the lightning angle with the line causes significant increase of the voltage and the effect of the earth resistivity on the induced voltage has been made clear when considering the inclined channel. Since the induced voltage is, in theory, proportional to the frequency of the inducing current, i.e. inversely proportional to rise time Tf when the inducing and induced circuits are parallel. When the lightning channel is angled, the proportional relation is less clear than that in the vertical channel. This fact has to be taken into account when discussing the effect of Tf. The current flowing in the earth is also affected by the lightning inclination and the voltage drop along the earth surface due to the current becomes larger than that in the vertical lightning case.

Electric Power Systems Research

This paper is focused on the oscillating frequencies of very-fast transients (VFTs) generated by ... more This paper is focused on the oscillating frequencies of very-fast transients (VFTs) generated by disconnector and circuit breaker operations in gas-insulated substations (GISs) related to electromagnetic disturbances (EMDs). Test results of the VFT amplitudes and oscillating frequencies are summarized, and the measured results have shown that there is no significant difference of the frequencies in the high-voltage main circuits and the low-voltage control circuits in the GISs. Modeling of GIS elements for VFT simulations by EMT-type software are explained, and simulation examples are demonstrated in comparison with test results. Also, FDTD (finite-difference timedomain) computations are performed, and the calculated results are compared with EMTP simulation results. If proper modeling is adopted, EMTP and FDTD results show a reasonable agreement.