| Most of the power lines are naked, therefore they are apt to be damaged by lightning stroke. The power supply is frequently interrupted and many electric devices are disabled under this kind of accident. As the fact that the direct lightning is more harmful than the indirect lightning, the study is focused on the direct lightning. For the 110kV and above high voltage overhead lines, the overvoltage of direct lightning is most imperil to the insulation, but this kind of lightning stroke is only about 10 percent of the whole. While owing to the low insulation level, almost 90 percent of the accidents are caused by the indirect lightning. In addition, with the development of the power system automation, more and more electrical devices are used in substation to collecting dates, controlling system and communicating. The voltage singles of these devices are too weak to withstand the various electromagnetic interference. Indirect lightning can interfere electric devices from many ways. It can interfere the electrical devices by conducting, that is, coupling to the device through electrical source line or single line. It can also influence even destroy the devices by the way of electric field coupling, magnetic field coupling or electromagnetic radiation. So it is of primary significance to study the interference caused by indirect lightning.The lightning includes cloud-to-cloud and cloud-to-ground strokes, among which the cloud-to-ground stroke is most serious to electric and electronic devices. The cloud-to-ground lightning can be classified into four categories, depending on the polarity of charge transferred to ground and direction of propagation of the initial leader: downward negative lightning, upward negative lightning, downward positive lightning, upward positive lightning. The downward negative lightning is the most common form, accounting for over 90% of all cloud-to-ground lightning worldwide. A lightning is usually include several strokes, among witch the first stroke is most harmful, so we emphasize the study on the first stroke.In this paper, we analyzed the lightning-induced voltages on overhead distribution lines; the shielding efficiency of reinforced concrete walls and shielded enclosure; measures of electromagnetic defense are putting forward. There are four parts in this dissertation:In part one (including chapter 1 and chapter 2) the improved transmission line model of lightning stroke is chosen as calculation modelamong many different models after careful comparison. It is very difficult to made a common lightning model, because every lightning shrike current is different. One acceptable model can only represents some information acquired from measurement, such as the lightning base current, the traveling speed of stroke, the electromagnetic field at a distance, and so on. As most measurements are taken at the ground level, the data acquired is usually related to the base current. A lightning model consists of two components: one is the waveshape of the base current, the other is the relationship of current at any height of lightning channel with the base current. There are two types of lightning base current model, the double exponential function model and the Heidler model. The modified transmission line model visualizes the return stroke as the propagation of current pulse from the ground end of the leader to the cloud end, it assumes that the shape and speed remain the same with height while the amplitude is exponentially decay with height. With this model the tip current becomes equal to 0. Hence the disadvantage of having a discontinuity at the stroke tip, which is presented in other models, is acoided.In this part, the electromagnetic field around lightning channel is calculated in both the time-domain and the frequency-domain. It is the fundamental part of this dissertation.In part two (including chapter 3 to 5), the telegrapher's equations which describe the coupling between the electromagnetic field of the lightning and the multiconductor transmission line are deduced from...
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