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For the rationalization of lightning protection design of distribution lines, it is important to clarify the behavior of distribution lines when direct or nearby lightning occurs. Because of the lower insulation level than for transmission lines, in studies on lightning protection design of distribution lines, not only direct lightning strokes but also induced voltages caused by nearby strokes must be taken into account. Thus, it is necessary to grasp the frequency of occurrence on lightning phenomena around distribution lines. For this aim, lightning phenomena on TEPCO's distribution lines in use had been continuously observed for 6 years (1996 to 2001). The observation was carried out in a composite way, using still cameras and sensor for acquisition of lightning surge waveform data. Through the observation, new phenomena about lightning performance on distribution lines in the field became apparent. In some cases, in spite of a direct strike to the line, flashover did not occur. This fact means that the distribution line has a certain level of lightning resistance. Moreover, it was confirmed that AC following current generated between both ends of insulator disappeared naturally. These results are interesting discoveries that can be useful in estimating the fault ratio precisely. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 157(1): 10–19, 2006; Published online in Wiley InterScience (http://www.interscience.wiley.com). DOI 10.1002/eej.20164 [ABSTRACT FROM AUTHOR]

Because of the lower insulation level than for transmission lines, in this study on lightning protection design of distribution lines, not only direct lightning strokes but also induced voltages caused by nearby strokes must be taken into account. Thus, it is necessary to grasp the frequency of occurrence of lightning phenomena around distribution lines. For this aim, lightning phenomena on TEPCO's distribution lines in use were continuously observed for 6 years (1996 to 2001). Through this observation, new interesting statistical data that can be a useful basis for rationalization of lightning protection design of distribution lines were obtained. Two hundred and four lightning strokes were observed through the six-year period. Probability of occurrence of a direct stroke was 22% (45 direct strokes were obtained). The fact that in 47% of direct strokes the electric outage did not occur is very interesting. Moreover, the value of surge discharge current of the arrester in the case of nearby stroke is the basis for conventional theory of grounding system. Therefore, statistical analysis of ZnO discharging current in the case of nearby strokes was carried out. As a result, in the case of nearby strokes, 5% value of cumulative frequency of discharging current is 0.5 kA. This value is half the conventional data. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 155(2): 8–16, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20180 [ABSTRACT FROM AUTHOR]

This paper presents the fundamental surge phenomenon when a step voltage is applied to a horizontal line above the ground which has branch feeders. We study line current and voltage at joint with the method of moments that calculates electromagnetic field in frequency domain. It is widely noted that the current reflection factor changes to a third at the junction of the same three lines in conventional transmission line theory based on TEM wave, and the stepwise current reflected appears overlapping to the incident current. On the other hand, the reflected current from the joint shows the inductive characteristic or the capacitive one depending on the angle between lines, which varies gradually and not stepwise in our numerical analysis considering TM wave. The time characteristic of the voltage at joint depends on the angles also, and the peak voltage slightly exceeds the voltage by the transmission line theory. These phenomena are caused by the electromagnetic coupling between the main line and branch lines. In addition to the computer simulations, we measured the currents in the reduced-scale model lines and the results show the validity of our analysis regarding changes of the reflected current depending on the angles. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 144(2): 1–8, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10176 [ABSTRACT FROM AUTHOR]