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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. Index Terms--Electromagnetic transient, lightning, lightning outage, lightning performance, lightning surge, tower surge response, transmission line, transmission tower.

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 Sunde's 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. Index Terms--Buried bare wire, electromagnetic compatibility (EMC), electromagnetic transient, Electromagnetic Transients Program (EMTP), ground grid, grounding system, lightning, lightning surge, transient response.

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, almost the same parts were damaged at the No. 3 transformer in Katayamazu substation. To investigate the cause of the transformer failures, observation apparatus were installed at four substations in the Higashikanazu power system. Approximately 490 waveforms of incident surge were measured during the observed period. In 11 cases, simultaneous measurements of the incident surge waveforms at the four substations were achieved. By the analysis of the observed waveforms, the specific frequency components were found. From the investigation of theoretical and analytical approaches, it became clear that these frequency components depended on the power system configuration. By comparing the specific frequency components of the observed waveforms and the natural frequency components of the transformer, it was clearly shown that the overvoltages due to the internal resonance phenomena were the cause of failures. As a result, the internal resonance phenomena should be considered in the design of transformers, and the specific frequency components should be also estimated by the theoretical and analytical approaches. Index Terms--Fast Fourier transform (FFT), frequency characteristic, internal resonance, lightning surge, natural frequency, power system, substation, transformer, voltage waveform, 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. Index Terms--Breakdown probability, natural frequency, resonance overvoltage, surge protection device, tap winding, transformer, winding form, winter lightning.

This paper investigates the charge versus voltage (q-v) curves of surge corona on transmission lines. Two measurement methods of the q-v curves are proposed, and field test results are shown to validate the methods. Since the new methods do not require a charge-measuring conductor, such as a corona cage, the q-v curves are measured in the real electric-field distribution. One of the methods obtains the amount of charges q by numerically integrating the digitally stored waveform of injected current, assuming that the line is short in length and open ended. Thus, it is suitable for measurement using an experimental setup. The other calculates q from voltage and current waveforms based on the traveling-wave theory, assuming that the line is long enough to expect no reflected waves, and it is applicable to existing 'real' transmission lines. Measured q-v curves are compared with simulated ones, and their physical properties are discussed in the paper. Index Terms--Charge measurement, corona, power transmission lines, space charge, surges.

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. KEYWORD - Air gaps; Lightning; Lightning surge; Leader developing method; EMTP; Insulation design; Back flashover.