Hideki Motoyama

Observation and analysis of multiphase back flashover on the Okushishiku Test Transmission Line caused by winter lightning

This paper describes observation and analysis of multiphase back flashover phenomena on the Okushishiku Test Transmission Line in the winter lightning season. Observation of lightning surges caused by natural lightning and rocket-triggered lightning strokes has been carried out on the test transmission line since 1987. From 1993 to 1996, lightning currents and voltages at the test transmission line were measured simultaneously for ten times. Especially, a four-phase back flashover was observed in 1994. A new calculation method of multiphase back flashover, which is based on the leader developing model, is proposed. Calculated results by the proposed method show good agreements with the observations.

Analytical and experimental study on surge response of transmission tower

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.

Measurement of lightning surges on test transmission line equipped with arresters struck by natural and triggered lightning

Measurement of lightning surges caused by natural or rocket-triggered lightning strokes has been carried out on a 275 kV test transmission line since 1987. In November 1993, lightning currents at the tower top, the ground wires, the tower legs and the transmission line arresters, along with the voltages across the insulator strings were measured simultaneously four times. One of the four flashes was natural lightning, and its peak value was +132 kA. In this case, the arresters operated, and the insulator voltages where the arresters were equipped were controlled properly. The result of a multi-phase analysis by EMTP agreed well with the measured waveforms.

Internal winding failure due to resonance overvoltage in distribution transformer caused by winter lightning

In this paper, we describe the internal winding failures of the no. 3 distribution transformer at Katayamazu substation caused by winter lightning. Almost the same internal winding part of the transformer was damaged in January 1997 and November 2001. Therefore, detailed investigations of the cause of failures were carried out. From the investigations on the measurement of the frequency characteristics of transformer windings and detailed lightning surge analysis used by Electromagnetic Transients Program (EMTP), it was found that resonance overvoltages were generated by resonance phenomena between the surge waveform passing through the transformer and the natural frequency characteristics of the transformer winding. This finding was used to improve the winding form of tap windings and install a surge protection device between tap windings. After the improvement of winding structures, it was clearly shown that the internal stress of tap windings was reduced and the breakdown probability of the damaged part was significantly reduced.

Electromagnetic Transient Response of Buried Bare Wire and Ground Grid

In this paper, experimental and analytical studies of the electromagnetic transient response of a buried bare wire and a ground grid are presented. The electromagnetic transient response of a ground grid has effects on induced surges in low-voltage and control circuits of power stations, substations, and telecommunication stations. Therefore, the experimental and theoretical examinations for the electromagnetic transients response of a buried bare wire and a ground grid have been carried out. However, these examinations need verifications with field tests in practical use. To solve these problems, the measurements of the electromagnetic transient response of the buried bare wire and ground grid are carried out under various experimental conditions. The experimental results are compared with results calculated using Sundes theoretical formulas, and the validity of the theoretical formulas is examined. Moreover, a calculation model based on both the theoretical formulas and electromagnetic transients program is proposed. From these examinations, it is clearly shown that the results calculated using the theoretical formulas can reproduce the experimental results.

Experimental Study on Lightning Surge Response of 500-kV Transmission Tower With Overhead Lines

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.

Reproduction of electromagnetic field waveforms and tower currents associated with return strokes struck Tokyo Skytree

Observation of lightning current by using Rogowski coils started in February 2012 at Tokyo Skytree, which is a 634-m high freestanding broadcasting tower. Electromagnetic field waveforms are also observed by capacitive antennas at several tens of kilometers from the tower. Lightning current and electric field waveforms simultaneously observed in May 2012 are reproduced by using an electromagnetic model of a return stroke with the help of NEC-4. Observed lightning current waveforms are well reproduced by modeling the tower with small number of thin wires. Electromagnetic field waveforms also are reproduced by an inclined lightning channel model reconstructed from still photographs.

Measurement of lightning currents at TOKYO SKYTREE ® and observation of electromagnetic radiation caused by strikes to the tower

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.

Calculation model to evaluate effects of lightning protection measures on railway signalling equipment

The development of the effective and economical protection measures is very important for the railway signalling systems because the lightning damages cause the disruption of the railway transportation systems. The authors have conducted the field tests to investigate the surge parameters along the rails and proposed a calculation model of surge propagation characteristics along the rails. In this paper, we propose a calculation model for lightning overvoltages on the railway level crossing system as typical railway signalling equipment. Moreover, this paper indicates the evaluation results of lightning protection effects by using the calculation model.

Analytical study on lightning overvoltages of rail track and railway signalling equipment

The development of the effective and economical protection measures is vital for the railway signalling systems because the lightning damages cause the disruption of the railway transportation systems. In general, the railway signalling systems are set up at a wayside and directly connected to the rails through cables. The lightning surges can invade the railway signalling systems via the cables and cause damages to the systems. Accordingly, clarifying the propagation characteristics of lightning surges along the rails is essential to develop the lightning protection measures for the railway signalling systems. We have carried out the field tests to examine both surge impedance and surge propagation velocity of the rails. This paper proposes a calculation model of the surge propagation characteristics along the rails. The results of surge impedance and surge propagation velocity calculated by the proposed model almost agree with the experimental results. Moreover, this paper proposes a calculation model of the lightning overvoltages on the railway signalling equipment. The calculation model consists of the rail model and the equivalent circuit model of signalling equipment. We indicated the validation of the calculation model of the railway signalling equipment due to the comparison with the results of the field test. This model is applicable to the development of lightning protection measures for the railway signalling systems.