TOKYO SKYTREE® has recently been constructed in the eastern area of central Tokyo, located in the Kanto Plain, and is the tallest free-standing broadcasting tower in the world (634m). When a tall structure is located on a plain, it is... more
TOKYO SKYTREE® has recently been constructed in the eastern area of central Tokyo, located in the Kanto Plain, and is the tallest free-standing broadcasting tower in the world (634m). When a tall structure is located on a plain, it is expected that lightning will often strike the structure when thunderclouds approach. The authors plan to observe the currents of lightning striking TOKYO SKYTREE and have installed Rogowski coils on the tower at a height of 497m. CRIEPI have also started to observe the electromagnetic radiation generated by lightning strikes to TOKYO SKYTREE. Hemispherical antenna to detect electric fields and loop coils to detect magnetic fields are located at various sites in the Kanto Plain. In this paper, the authors report their plan to conduct measurements using these coils and the system used for electromagnetic observation.
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Electromagnetic transient response (ground potential rise (GPR) and/or resistance) of a grounding electrode is a parameter essential for the insulation and EMC designs for electric power systems and information and communication systems.... more
Electromagnetic transient response (ground potential rise (GPR) and/or resistance) of a grounding electrode is a parameter essential for the insulation and EMC designs for electric power systems and information and communication systems. Many researchers have studied the electromagnetic transient responses of grounding electrodes to date. However, results obtained from their studies are practically inapplicable to the insulation and EMC designs because their studies mainly focused on the steady state phenomena of grounding electrodes. With the aim to clarify the characteristics of the electromagnetic transient responses of grounding electrodes, my research group has carried out a series of experiments. The experiments were conducted for three different grounding electrodes: a 30 m vertical electrode, a tower foot and a buried bare wire. The comparison between time and frequency characteristics demonstrated that the spike-shaped transient resistance appearing in the wave front of transient GPR corresponded to the surge impedances peculiar to the electrodes. In addition, the transient GPR of these electrodes changed with time and converged toward the steady state resistance. GPRs observed around the electrodes gradually decreased from the peak value of the transient GPR as the distance from the electrodes increased. These results are useful in evaluating the transient electromagnetic response of grounding electrodes.
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This paper describes observations of lightning current waveform at Tokyo Skytree, which stands in the eastern area of central Tokyo, located in the Kanto Plain, and is a 634-m high freestanding broadcasting tower. Direct observation of... more
This paper describes observations of lightning current waveform at Tokyo Skytree, which stands in the eastern area of central Tokyo, located in the Kanto Plain, and is a 634-m high freestanding broadcasting tower. Direct observation of lightning current by using a pair of Rogowski coils started in the end of February 2012. From 2012 to the end of 2013, currents associated with 24 lightning flashes which hit the tower were recorded. In 2012, most of the flashes were upward as was expected; however, in 2013, most of the flashes observed in summer were downward. We have also evaluated statistical characteristics of obtained lightning current waveforms.
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Research Interests: Computer Science and EMTP
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ABSTRACT This paper has investigated switching surge characteristics in low-voltage control circuits transferred from main circuits of gas insulated substations through measuring voltage transformers (VT) and current transformers (CT)... more
ABSTRACT This paper has investigated switching surge characteristics in low-voltage control circuits transferred from main circuits of gas insulated substations through measuring voltage transformers (VT) and current transformers (CT) based on field measurements and EMTP simulations. The oscillating frequency of the switching surges in main circuits ranges from some MHz to some 10 MHz, and the surge voltages on a control cable are from some 10 V to 300 V in the EMTP simulation. The simulation results agree with the field measurements of the oscillating frequency ranging from 2 MHz to 80 MHz, which don't support the IEC 61000-4-12 recommended frequency 100 kHz and 1 MHz. The measured voltages range from 10 V to nearly 500 V. Mutual coupling between the main circuits and the control cable induces a high frequency oscillating voltage which are superposed on the transferred voltage. Grounding the both ends of the control cable metallic sheath produces another oscillation due to a circulating current in a closed loop composed of the sheath and the grounding circuit.
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Horizontal grounding conductor is often used to obtain low grounding resistance. Simulation results of voltages and currents in a circuit including a grounding system are sometimes different from measured results because the grounding... more
Horizontal grounding conductor is often used to obtain low grounding resistance. Simulation results of voltages and currents in a circuit including a grounding system are sometimes different from measured results because the grounding resistance depends on temperature and water content. Lightning surge characteristics of a grounding conductor are important for lightning protection design. Simple formulas for the surge characteristics of the grounding conductor are useful for engineers to estimate the influence of parameters of grounding system on lightning overvoltages. This article describes measurement results of the surge characteristics of grounding conductors for various conductor lengths and terminal conditions. This article proposes simple formulas for surge impedance and propagation velocity of horizontal grounding conductor based on the measured results. A simple equivalent circuit of grounding conductor is described. The constants of the equivalent circuit are obtained using the proposed formulas. Simulation results of voltage on a grounding grid using the proposed formulas and the equivalent circuit of grounding conductor are compared with experimental results.
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Abstract This paper presents the observation results of surge waveforms in substations and the frequency components of such waveforms. In the Higashikanazu 77 kV power system, distribution transformers were damaged three times by winter... more
Abstract This paper presents the observation results of surge waveforms in substations and the frequency components of such waveforms. In the Higashikanazu 77 kV power system, distribution transformers were damaged three times by winter lightning. In particular, ...
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ABSTRACT This paper has investigated switching surge characteristics in low-voltage control circuits transferred from main circuits of gas insulated substations through measuring voltage transformers (VT) and current transformers (CT)... more
ABSTRACT This paper has investigated switching surge characteristics in low-voltage control circuits transferred from main circuits of gas insulated substations through measuring voltage transformers (VT) and current transformers (CT) based on field measurements and EMTP simulations. The oscillating frequency of the switching surges in main circuits ranges from some MHz to some 10 MHz, and the surge voltages on a control cable are from some 10 V to 300 V in the EMTP simulation. The simulation results agree with the field measurements of the oscillating frequency ranging from 2 MHz to 80 MHz, which don't support the IEC 61000-4-12 recommended frequency 100 kHz and 1 MHz. The measured voltages range from 10 V to nearly 500 V. Mutual coupling between the main circuits and the control cable induces a high frequency oscillating voltage which are superposed on the transferred voltage. Grounding the both ends of the control cable metallic sheath produces another oscillation due to a circulating current in a closed loop composed of the sheath and the grounding circuit.
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This paper presents a comparison between the measured and calculated results of tower surge response for verifying the accuracy of lightning surge analysis. These calculated results are obtained using the Finite Difference Time Domain... more
This paper presents a comparison between the measured and calculated results of tower surge response for verifying the accuracy of lightning surge analysis. These calculated results are obtained using the Finite Difference Time Domain (FDTD) method and the Electromagnetic Transients Program (EMTP). Injection current waveforms and voltage waveforms across insulator strings of the transmission tower were measured when a rectangular impulse current or a current with the rise time of 1µs were injected into the top of the tower. The measured waveforms of voltage across insulator strings are compared with the calculated voltage waveforms using the FDTD method. The calculated waveforms can reproduce the measured waveforms, and as a result, it is verified that the FDTD method is effective in a lightning surge analysis. The influences of the geometrical arrangement of phase wires, the ground resistivity and the slope of ground on the accuracy of a surge simulation are also investigated using...
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This paper describes a new approach of the lightning surge analysis for an air-insulated substation (AIS). The lightning impulse withstand voltage (LIWV) level of electric power facilities in substations and power stations is determined... more
This paper describes a new approach of the lightning surge analysis for an air-insulated substation (AIS). The lightning impulse withstand voltage (LIWV) level of electric power facilities in substations and power stations is determined by the lightning overvoltage. This is calculated by the lightning surge analysis using an electromagnetic transients program like EMTP (Electromagnetic Transients Program). The proposed approach for the lightning surge analysis of the AIS employs the multi-phase constants parameter model (M-CP model) line. It is theoretically difficult to apply the conventional model using multiphase lines when the length of the bus conductor is short. The proposed approach demonstrates high accuracy by comparing the experimental results and the finite-difference timedomain (FDTD) method. From the examinations, it is also clearly shown that the LIWV of a present AIS could be reduced, if the proposed approach for the lightning surge analysis and high performance metal...
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The present situations of superconducting electric power machines in the world and studied problems were investigated from viewpoint of the electric insulation. 50MVA generator (CRIE/Hitachi) or 120MVA generator (KWU/Siemens) where the dc... more
The present situations of superconducting electric power machines in the world and studied problems were investigated from viewpoint of the electric insulation. 50MVA generator (CRIE/Hitachi) or 120MVA generator (KWU/Siemens) where the dc superconducting technique was applied on field windings, are developed. As to Superconducting transformer, 220KVA transformer is trially manufactured and the conceptual design of 1,000MVA transformer is made by W.H. or Alstom. Future problems are the study of protecting method for the overvoltage to superconducting electric power machines and the study to prevent the quench for superconducting windings. The respective insulating characteristics of solid and liquid insulators become clear gradually under the cryogenic condition but a large part of insulating characteristics of composite insulator prepared by combination of both insulators are not clear, so that these problems must be clarified.
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ABSTRACT The operating voltages of low-voltage control circuits in power plants and substations have become lower owing to the installation of digital-control equipment. This significantly increases the risk of faults and malfunctions of... more
ABSTRACT The operating voltages of low-voltage control circuits in power plants and substations have become lower owing to the installation of digital-control equipment. This significantly increases the risk of faults and malfunctions of such circuits due to abnormal voltages in the control circuits induced by lightning and switching surges. Therefore, the prediction of the induced voltages is strongly required for protecting such circuits from abnormal voltages. Recently, the FDTD (Finite Difference Time Domain) method, which solves Maxwell's equations numerically, is applied to the simulation of surge phenomena on conductors placed in three-dimensional arrangements such as transmission towers and buildings. The FDTD method can easily take into account the finite conductivity and relative permittivity of the ground soil and ground structure in detail. These parameters affect the induced voltages on control circuits. In this paper, first, we perform the FDTD calculations for a grounding grid whose size corresponds to a distributing-substation area. Second, we calculate the potential rises of the grounding grid, currents flowing through the grounding grid, and induced voltages on a control wire above the grid. Comparing the calculated results with the measured ones, we confirm the applicability of the FDTD method to the calculation of the induced voltages on the control wire generated by current flowing into the grounding grid.
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Research Interests: Power Electronics, Electromagnetic Compatibility, Comparative Study, Ground Effect, Power Generation, and 11 moreElectromagnetic modeling, Lightning, Field Experiment, Grounding, Transients in Electrical power Systems, Electro Magnetic, Transient Response, Electrical And Electronic Engineering, Low voltage, GROUNDING system, and Power station
This paper describes experimental study and analysis of breakdown characteristics of long air gaps with short tail lightning impulse, which appears across the insulator strings on the transmission line by a lightning stroke. At first,... more
This paper describes experimental study and analysis of breakdown characteristics of long air gaps with short tail lightning impulse, which appears across the insulator strings on the transmission line by a lightning stroke. At first, starting conditions of leader propagation and leader developing process with the short tail lightning impulse are clarified by experiments. A new flashover model based on the experimental results is proposed in this paper. The proposed model consists of simple two equations, that give expression to the leader developing process, and can be realized very easily on the EMTP and other transient`s programs. A comparison of results calculated by the proposed model with the experimental results shows good agreements.
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ABSTRACT This paper presents the measurement of the lightning surge response of a 500-kV transmission tower with overhead lines including ground wires and phase wires. A number of experimental studies on the lightning surge response of... more
ABSTRACT This paper presents the measurement of the lightning surge response of a 500-kV transmission tower with overhead lines including ground wires and phase wires. A number of experimental studies on the lightning surge response of transmission towers have been carried out using freestanding structures such as scale models or actual transmission towers. However, these experiments have ignored the effects of transient electromagnetic coupling among the injection current, the overhead lines, and the tower. This paper reports a new method of measurement considering the arrangement of an actual tower and overhead lines. It is clearly shown that the measured voltage waveform across insulator strings at each crossarm depends on the direction of the injection current. Moreover, the measured current value flowing into the ground wires varies with the direction of the injection current. These results predict that the surge response of a transmission tower depends on the direction of the return stroke current. This is important for the modeling of towers with overhead lines and the estimation of the lightning performance of transmission systems under a lightning stroke.
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ABSTRACT The present paper describes a lightning surge calculation including the wave deformation due to corona. The corona wave deformation is represented by a linear corona model consisting of R-C parallel circuits with diodes, which is... more
ABSTRACT The present paper describes a lightning surge calculation including the wave deformation due to corona. The corona wave deformation is represented by a linear corona model consisting of R-C parallel circuits with diodes, which is easily achieved by the electromagnetic transients program, EMTP. This simple corona model gives satisfactory accuracy compared with field test results. The lightning surge calculation was carried out using a two-conductor model consisting of a phase wire from which a back-flash occurs, and an equivalent ground wire. The two-conductor model gives almost the same accuracy as that using a multiconductor full representation model, for example an eight-conductor model for a twin-circuit line with two ground wires, with a computation time and memory less than a half those of the full representation model.It is observed from calculated results that the corona, in general, reduces voltages at towers and substations by more than 10%. The wave deformation due to the frequency-dependent effect of a transmission line generally has no significant effect on a lightning surge, and thus may be neglected in a lightning surge calculation.
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In this paper, the authors propose a concept of the voltage dip hazard map. It visualizes the magnitude and occurrence probability of instantaneous voltage dips caused by lightning in consideration of the frequency distribution of... more
In this paper, the authors propose a concept of the voltage dip hazard map. It visualizes the magnitude and occurrence probability of instantaneous voltage dips caused by lightning in consideration of the frequency distribution of lightning and all inter-connected networks on a system. This map clarifies the characteristics of voltage dips on a system from several aspects such as magnitude and occurrence probability of voltage dips at each consumer, the distribution of them on the system, and the relationship between regional lightning frequency and voltage dips. We show an example of the map using a ten generators model and verify the availability of the proposed concept.
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ABSTRACT We summarize the lightning data for 17 years from 1992 to 2008 obtained with lightning location systems of nine electric power utilities in Japan and analyze them. The observed annual number of lightning flashes of which the... more
ABSTRACT We summarize the lightning data for 17 years from 1992 to 2008 obtained with lightning location systems of nine electric power utilities in Japan and analyze them. The observed annual number of lightning flashes of which the current is more than 10 kA is 400 000–800 000 and the 50% value of the cumulative distribution of lightning peak currents is about 23 kA in recent times. The variation of lightning occurrence characteristics by areas, seasons, and so on, is clarified. Comparison of the obtained data with those obtained by another lightning location system is also made. The relationship between lightning occurrence and climate is discussed. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.
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ABSTRACT This paper describes analytical and experimental studies on tower surge response, including effects of return stroke current. Such effects have been ignored in previous lightning surge analyzes of transmission towers. A new... more
ABSTRACT This paper describes analytical and experimental studies on tower surge response, including effects of return stroke current. Such effects have been ignored in previous lightning surge analyzes of transmission towers. A new method for calculating transmission tower surge response including the effects of return stroke current is proposed. The proposed method is based on the electromagnetic field theory, and it clearly shows that the tower surge response depends on the direction and velocity of the return stroke current. The tower surge response calculated by the proposed method agrees well with the measured tower surge response obtained from scale model tests and field tests
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ABSTRACT Lightning surge analysis is very important from the viewpoint of insulation design of transmission lines and substations. Lightning surge analysis has many parameters, which include lightning surge characteristics of transmission... more
ABSTRACT Lightning surge analysis is very important from the viewpoint of insulation design of transmission lines and substations. Lightning surge analysis has many parameters, which include lightning surge characteristics of transmission towers, back flashover phenomena at an arcing horn, characteristics of footing resistance, effects of corona wave deformation, characteristics of electromagnetic fields caused by lightning, and other parameters. This paper describes experimental and analytical studies on lightning surge characteristics of a buried bare wire. The measurement of the lightning surge characteristics of the buried bare wire is carried out under various experimental conditions. The experimental parameters controlled in these experiments include earth resistance, length of the buried bare wire, and waveform of the injected current. The measured results are compared with analytical results based on the theoretical study by Sunde. A comparison of the measured results with the analytical results shows good agreement. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 164(3): 35– 41, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20532