Numerical Study On The Effect Lightning Distance Of Tall Buildings To Surrounding Buildings

Cloud-to-ground lightning process has a great impact on our production activities. Although the lightning protection methods have some limitations at present, it is necessary to adopt the leader development model to conduct a research of the relationship between lightning and ground objects. It is not only beneficial to understand the physical mechanism of lightning propagation, but also more valuable to the research of how to apply lightning protection measures to constructions. In this paper, the main works has two parts:First is the study of corona trigger threshold. The second part is that after the tips of buildings occur corona discharge, upward leader which the respective tip triggers connects with the downward leader from a thunderstorm. The main research results of each part are as follows:(1) We got the corona pulse waveform when the mental tips were producing corona discharge through laboratory test. The result showed that along with the higher voltage, corona pulse frequency increased. As the plate voltage decreasing, pulse amplitude decreased as well; when the plate voltage dropped to a fixed value, the corona pulse would disappear immediately. The corona voltage threshold increased, and this change was in accord with diameter and in contrast with height. But after the calculation of mental tips electric field suggested that cylindrical tip was likely to have a fixed corona trigger threshold electric field that Ec=736.096kV/m as same as the taper-cylindrical tip which Ec=215.58kV/m. Under the action of positive voltage source, each metal tip of the corona inception voltage was lower than the voltage value corresponding to the negative voltage source.(2) According the model results we found that when the lightning stroke multiple buildings, tall buildings had shielding effect to low buildings, and there was a critical protection distance value. When fixed the height and width of the tall and low buildings, by changing the distance between the two buildings founded, the low buildings were not suffered by lightning strike or the probability of lightning strike was tiny within the threshold. Otherwise when exceeding the critical distance value, the probability of low buildings struck was enhanced with the distance. Furthermore, the critical protection distance and the height of high buildings had a positive correlation, and the height of low buildings has a negative correlation. We also summarized the correlation equation between critical protection distance and the height of tall & low buildings.(3) The protection scope of different buildings height was simulated, and we founded that even the initial position of downward leader was over the buildings, lightning would not certainly hit the buildings; even if the initial position of downward leader was far away from buildings, the lightning has a great hit rate which was the stochastic characteristic of the lightning strike location. Besides, the results showed that with the increased of the buildings height, the protection scope showed increased trend. Moreover the protection radius obtained from model were larger compared with the protection scope of rolling sphere method, and the bias increased with the buildings height.