9/12/2023 0 Comments Lightning rod system![]() ![]() ![]() Lightning damage has been with humanity since people started building structures. Wooden church with lightning rods and grounding cables The results of this study suggest that moderately blunt metal rods (with tip height–to–tip radius of curvature ratios of about 680:1) are better lightning strike receptors than are sharper rods or very blunt ones. Since the field strength at the tip of a sharpened rod tends to be limited by the easy formation of ions in the surrounding air, the field strengths over blunt rods can be much stronger than those at distances greater than 1 cm over sharper ones. As a result, at a few centimeters above the tip of a 20-mm-diameter blunt rod, the strength of the field is greater than that over an otherwise similar, sharper rod at the same height. "Lightning Rod Improvement Studies" by Moore et al say: Calculations of the relative strengths of the electric fields above similarly exposed sharp and blunt rods show that although the fields, prior to any emissions, are much stronger at the tip of a sharp rod, they decrease more rapidly with distance. According to field research, a rod with a rounded or spherical end is better. It is commonly believed, erroneously, that a rod ending in a sharp point at the peak is the best means to conduct the current of a lightning strike to the ground. Lightning rods should be placed where they will prevent the sphere from touching a structure. Points which the sphere cannot roll across and touch are safest from lightning. At each point we are simulating a potential leader position and where the sphere touches the ground the lightning is most likely to strike. To determine which strike points consider a sphere rolling over the terrain. Noting this, locations that are safe from lightning can be determined by imagining a leader's potential paths as a sphere that travels from the cloud to the ground.įor lightning protection it suffices to consider all possible spheres as they touch potential strike points. It is standard practice to approximate the sphere's radius as 60 m near the ground.Įlectricity travels along the path of least resistance, so an object outside the critical distance is unlikely to be struck by the leader if there is a grounded object within the critical distance. Objects are likely to be struck if they are nearer to the leader than this critical distance. ![]() The maximum distance that each step may travel is called the critical distance and is proportional to the electrical current. As the step leader of a lightning bolt jumps toward the ground, it steps toward the grounded objects nearest its path. To understand this requires knowledge of how lightning 'moves'. This has been found to be unsatisfactory for protecting taller structures, as it is possible for lightning to strike the side of a building.Ī better technique to determine the effect of a new arrester is called the rolling sphere technique and was developed by Dr Tibor Horváth. Historical understanding of lightning assumed that each rod protected a cone of 45 degrees. Electrical substations usually have a web of the lighter conductor wires covering the whole plant.Ĭonsiderable material is used in the construction of lightning arresters, so it is prudent to work out where a new arrester will have the greatest effect. This conductor is grounded at various points along the link. Similarly, high-tension power lines carry a lighter conductor wire over the main power conductors. In telegraphy and telephony a lightning rod is placed where wires enter a structure, preventing damage to electronic instruments within and ensuring the safety of individuals near them. If the underground cable will resist corrosion well, it may be covered in salt to improve its electrical connection with the ground. Ideally, the underground part of the assembly should reside in a muddy area, or an area that tends to become so during storms. Lightning rods sometimes possess a short circuit to the ground that is interrupted by a thin non- conductor over which lightning jumps. The term 'lightning rod' is also used as a metaphorical term to describe those who attract controversy.Ī lightning rod is connected via a low- resistance wire or cable to the earth or water below, where the charge may be safely dissipated. Sometimes, the system is informally referred to as a lightning conductor, lightning arrester, or lightning discharger however, these terms actually refer to lightning protection systems in general or specific components within them. Its formal name is lightning finial or air terminal. An example of a standard, pointed-tip air terminalĪ lightning rod (or lightning protector) is a metal strip or rod, usually of copper or similar conductive material, used as part of lightning safety to protect tall or isolated structures (such as the roof of a building or the mast of a vessel) from lightning damage. ![]()
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