Lightning damage and lightning protection measures

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Lightning damage and lightning protection measures for low voltage distribution lines in Japan

1 Overview in a wide area, many complex and huge power equipment have been built to form a high-voltage and low-voltage distribution network in which the aluminum consumption of North American car bodies will reach 1million tons in 2017. There are distribution equipment and useful electrical equipment in the distribution network. They are important equipment that affect the quality of power energy. Figure 1 is a schematic diagram of standard equipment designed by TEPCO. Up to now, the lightning protection measures for distribution lines mainly focus on: (1) how wide the impact range of lightning accident caused by Lightning Overvoltage on a high-voltage distribution line and the probability of its possibility; (2) Determine the degree of lightning protection; (3) Formulate various lightning protection measures that can be used on the actual distribution line. For example, on low-voltage distribution lines with single-phase 100/200v or three-phase 200V, the burning out of low-voltage distribution equipment caused by lightning overvoltage and the misoperation of leakage shape shall be considered. Spark discharge caused by lightning overvoltage is not the cause of burning low-voltage distribution equipment. This spark discharge leads to short circuit between terminals of distribution equipment. Under commercial power frequency voltage, short-circuit current (arc discharge) flows between terminals. At this time, a large amount of electric energy is the main cause of burning low-voltage distribution equipment. The arc characteristics of low-voltage distribution equipment are different from those of high-voltage power system. Continuous current arc may not occur after spark discharge between terminals, which is the unique performance of low-voltage distribution system. 2. the frequency of Lightning Overvoltage on low-voltage distribution lines. Lightning Overvoltage on low-voltage distribution networks in very wide areas has the function of experimental force, displacement, time and dynamic display of experimental curves. The voltage is affected by the terrain, meteorological conditions, thunderstorm days, the moving path of thunderstorms, the peak lightning current, the erection density of high-voltage and low-voltage distribution lines, and the mine strike density. Among these factors, it is important to make clear statistics on the frequency of lightning overvoltage peak on low-voltage distribution lines. In order to obtain the basic data for studying the lightning protection measures for low-voltage distribution lines, during the lightning prone period from July to October 1981 to 1987, more than 110 surge counters were installed on the low-voltage distribution lines in Tochigi county and other areas to observe more than 460 lightning overvoltages, and statistical data and other detailed data were obtained. According to the observation results of this study, the probability of occurrence on low-voltage distribution lines is calculated. In the study of lightning proof design, the most basic lightning overvoltage frequency distribution curve (the line above) shown in Figure 2A shall be available. In this observation, from the lightning overvoltage above 2KV, the lightning overvoltage worried about spark discharge in the terminal board or equipment of low-voltage distribution equipment is assumed to be the 10kV limit. The cumulative frequency observed above 10kV is about 10%, while the cumulative frequency observed below 5kV is about 70%. Another observation result is that in a very narrow area, the surge counter is installed on the same low-voltage distribution line. In this case, 1 has a large gap and 187 cumulative observations have been made. Comparing the cumulative frequency of lightning overvoltage of the two observation results, their respective double logarithm curves of frequency distribution are similar to a straight line. But the two straight lines are not exactly the same. This is because the lower limit value of lightning overvoltage set on the surge counter is different. For example, in this observation, we are using our expertise in extrusion and thermoplastic lightweight structures, the lower limit value of lightning overvoltage is 2KV, while it is set as 1.2KV in some literatures. 3. Lightning Overvoltage on low-voltage distribution lines from the research on lightning protection measures on distribution lines, it has been considered that the factors of Lightning Overvoltage on low-voltage distribution lines are: 1 direct lightning strike (direct lightning strike on low-voltage distribution lines); 2 induction lightning (induction lightning generated by induction to the distribution line when lightning strikes the area near the low-voltage distribution line); 3 the lightning overvoltage at the high-voltage side is the cause of the lightning overvoltage invading the low-voltage side. Due to the action of the lightning arrester, the earth (grounding) potential rises, and the lightning overvoltage transits from the high-voltage side of the transformer on the column to the low-voltage side. In fact, in addition to the occurrence of Lightning Overvoltage on the low-voltage distribution line, lightning current directly invades the lightning rod set on the building near the distribution line, making the earth potential rise and affecting the field of the grounding system of the distribution equipment

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