![]() It cannot be used on objects of great height, as there are recommendations to protect against downstream lightning. Instructions on lightning protection IS 153-34.21.122-2003 is applied for buildings, structures and industrial communications, not exceeding 150 m. ![]() Principles of settlement and determination of protection zones of high-rise lightning rods are regulated by several accepted documents, but the formulas offered in them do not always remain relevant. The peculiarities of operation of lightning rods when installed on high-rise buildings Their possible trajectories are unpredictable. The first often overshoot and can affect not only the side surfaces of the object, but also the surrounding area. The main difference between the downstream and upstream breakdown is in the accuracy of their impact. Performing the design of lightning protection, it is necessary to take into account that at the altitudes below 200 m, the total number of atmospheric discharges drawn is also calculated by the above formula, but the percentage of upstream lightning begins to increase proportionally to the distance the top of the object from the ground surface. Lightning strikes the Ostankino TV tower* When binding in these cases the theory with the reality, the match percentage is close to 100, if not to take into account a small feature: the downstream discharges hit the tops only in half cases from the calculated values, the rest of the lightning are ascending, and their motion starts from the upper points of the objects.įigure 1. At the same time a 100 m building will attract a lightning discharge once a year, and 200 -meters-building four times more often. Lightning strikes into the highest point of the object 30 m high approximately 0.1 times per year (the probability is indicated at the absence of higher buildings nearby). Long and meticulous observations after the already exploited sites confirm the existence of a direct quadratic dependence of the amount of projected lightning strikes on the height of the top of the structures under consideration. On the major part of the Russian territory, this index is equal to 3, although for some regions it may reach 10. Where n M - the average number of discharges per year per 1 km 2 of the smooth ground surface of the selected region. ![]() The possible number of strikes can be described by the formula This isolated group presents itself a rod having a predetermined height h and which is able to attract lightning in the radius of 3h. To carry out a simple analysis to determine the expected number of lightning strikes in high-rise buildings, it is better to treat them as a separate group significantly exceeding the nearby objects in height. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |