Research On The Electromagnetic Influences Of Lightning On The Buildings And Transmission Lines

Lightning is a frequent electromagnetic phenomenon in the nature which can cause power outages, equipment trouble, personal injury and other safety accident, so it is necessary to take the lightning protection and natural disaster reduction as a long-term goals. Lightning will produce a greater threat to the buildings and transmission lines near the lightning channel, but the research on the distribution regularities of electromagnetic field in the vicinity of the lightning channel just starts and lacks of systemic understanding.This dissertation is supported by the Fundamental Research Funds for the Central Universities (14MS90) "Research on electromagnetic disturbance of lightning on the buildings and transmission lines", and emphatically carry out the research on the electromagnetic influences of lightning on the buildings and transmission lines. The main contents are as follows:The leader model, channel base current model and the return stroke model are proposed. Analyzing the physical mechanism of lightning development, the parameters such as radius, speed, current and charge can be used to describe the characteristics of lightning channel. In the leader channel model, the thundercloud, lightning channel and ground can be treated as electric quasi static field. The channel base current model uses the improved Heilder function, and build the return stroke model which considers the charges carried by the thundercloud and lightning channel. In the return stroke model, the thundercloud, lightning channel and ground can be treated as magnetic quasi static field.The computational method of the electromagnetic field in the vicinity of the lightning channel is proposed. Before lightning leader arrives to ground, the electric field is induced by the charges in the cloud, lightning leader and the induced charges on the ground. During the return stroke, the electric field is induced by return stroke current and the charges deposited in the thundercloud and lightning channel, and the magnetic field is excited by the return stroke current. Based on the models, deduce the the electromagnetic field in the vicinity of the lightning channel. The calculated electromagnetic fields are compared with the measured, and the effectiveness of the method is proved.Based on the equivalent transmission line model, the lightning current distribution in the lightning protection system (LPS) is calculated. Considering structural features of LPS and the spectrum character of the lightning current, a numerical model is built based on equivalent transmission line networks, the electromagnetic coupling between the lightning channel and LPS is considered. This dissertation adopts improved discrete complex images method (DCIM) to extract the quasi-static item and the low frequency approximation item from the kernel function, and this method can improve the computational efficiency. The calculated results are compared with the measured by the International Center for Lightning Research and Testing, and the effectiveness of the method is proved.An approach based on the partial element equivalent circuit technique (PEEC) has been proposed to analyze the transient current distribution in the LPS. The lightning channel is modeled as distributed parameter circuit, and the electromagnetic coupling between the lightning channel and LPS is modeled by means of partial inductances. The calculated results are compared with the literature, and the effectiveness of the method is proved. Due to the number of conductors is bigger, in order to facilitate the calculation, this dissertation writes partial inductance calculation procedure which can be calculate the partial inductance quickly and efficiently.This dissertation proposes the concept of improved shielding angle. Extracts the slope angle, slope aspect by use of digital elevation model (DEM), deduces the computing method of improved shielding angle under different topographic condition, and analyzes the influence of slope angle and slope aspect on lightning trip out rate, unify the influence of terrain factors on the shielding failure performance with the improved shielding angle. This dissertation proposes a set of evaluation process covering pre-assessment and re-evaluation. Combining with operational experience and environmental characteristics, the pre-assessment system determines the easily hit segment based on regulation method, then the easily hit segment will be modeled by improved the Electrical Geometric Model method and ATP/EMTP simulation computing technology. The feasibility and effectiveness has been proved through instance analysis.