2012 International Conference on Lightning Protection (ICLP), 2012
TOKYO SKYTREE® has recently been constructed in the eastern area of central Tokyo, located in the... 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.
Electromagnetic transient response (ground potential rise (GPR) and/or resistance) of a grounding... 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.
2014 International Conference on Lightning Protection (ICLP), 2014
This paper describes observations of lightning current waveform at Tokyo Skytree, which stands in... 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.
ABSTRACT This paper has investigated switching surge characteristics in low-voltage control circu... 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.
IEEE Transactions on Electromagnetic Compatibility, 2021
Horizontal grounding conductor is often used to obtain low grounding resistance. Simulation resul... 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.
2012 International Conference on Lightning Protection (ICLP), 2012
TOKYO SKYTREE® has recently been constructed in the eastern area of central Tokyo, located in the... 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.
Electromagnetic transient response (ground potential rise (GPR) and/or resistance) of a grounding... 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.
2014 International Conference on Lightning Protection (ICLP), 2014
This paper describes observations of lightning current waveform at Tokyo Skytree, which stands in... 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.
ABSTRACT This paper has investigated switching surge characteristics in low-voltage control circu... 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.
IEEE Transactions on Electromagnetic Compatibility, 2021
Horizontal grounding conductor is often used to obtain low grounding resistance. Simulation resul... 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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Papers by Hideki Motoyama