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Lightning --- A Case Study Dr Anil Kumar Tripathy , faculty GHITM Puri , Odisha Abstract---- Concept behind Lightening are a discharge of electricity & involve a very high electrical energy discharge and may put an adverse effect to structural damage , machinery /equipment and puts fatal effect to human beings and animal life when comes in contact . The paper gives an ample of ideas related to protection, effect and provides a solution for the cause behind it. Keywords: Lightening origination, Charge separation, Cloud cover factor, Temperature Gradient, Effects, Protection Provider Mechanism, etc. 1. Introduction--The mechanisms behind lightning are a discharge of electricity & involve a very high electrical energy discharge caused by the difference in potential between clouds or between the clouds and the ground. Clouds are formed in the upper atmosphere. The air around the lightening heats the air forming a channel with temperature 0f 30,000 0k and currents are more than 20 kA in 80% of cases and can reach in the region of 200 kA (or even more) with rise times of a few microseconds (source CIGRE – Electra no. 41 and 69). II. MECHANISM OF LIGHTNING The mechanism behind lightening is based on separation of charges of the thunderstorm which carries a positive charge on top & negative charge on bottom. The ground below the storm also develops a positive charge. As a result there exist differences in electrical potential which is caused for freezing of water to form ice crystals due to thermo-electric effect. In this process electrons flow from colder to warmer areas due to thermal gradient (electrical gradient). Since electrons carry a negative charge, the ice crystal then has a negatively charged core and a positively charged outer edge. A positive charge develops in the ground below the storm. When a lightning bolt jumps from one place to another, it originates in an area of negative charge and moves to an area of positive charge. The flow of electricity between the two then reduces some of the difference in electrical potential. Electricity may flow up and down the channel several times in the course of a single lightning strike. Depending on the direction in which the charge develops (cloud-to-ground or ground-to-cloud) and whether the charge is negative or positive, there are four different types of ground lightning strike. i. ii. iii. iv. Negative cloud-to-ground Positive ground to cloud Positive cloud to ground Negative ground to cloud -- -- -- + + +++++ ++++++ - - - - - - -- - - - - - - - - - Negative Positive Cloud - to- ground -toGround cloud Positive cloud -toground Negative ground - tocloud III. EFFECTS OF LIGHTNING Further sub divided into direct and indirect effects. A) Direct effects (strikes on structures) The simplest way to catch up structural effect will follow a path to ground layer through either lightning protection system or metallic path. In another way it may put directly strike to Electrical appliance (power lines, antennas, antenna feeders and overhead telephone cables) as well as mechanical services like water and gas piping. It may put a fatal state to human beings. Mechanism --At the point of contact, lightning generate a. Thermal effects caused by the electric arc b. Thermal and electrodynamics effects induced by circulation of the lightning current Protection against the direct effects of lightning is based on catching the current and discharging it to earth (lightning conductor, catcher rods, etc). B) Indirect effects Indirect effects of lightening may leads to damage in three ways voltages as caused by transient over - a. By conduction process which may put direct lightning strikes on lines (power, telecommunications, TV, etc.) entering or exiting buildings - b. By feedback process from earth via the earthing system, the protective conductors and the exposed conductive parts of equipment - c. by induction process in the installation's conductive elements (structure of the building, etc.) and internal lines (power, telecommunications, etc.) The effects of lighting can be felt by induction within a 1 km radius, and by conduction (feedback from earth and strikes on lines) within a radius of more than 10 km. Statistically, damage to electrical installations and equipment is mainly the result of the indirect effects of lightning strikes and over-voltages from operations, against which it is important to provide protection by installing voltage surge protectors. Mechanism – In two ways 1. When lightning current falls on a lightning conductor causes an overvoltage between the earthling system and the internal lines within the installation. Through distribution network overvoltage spreads to neighboring installations & strike hits the ground near the building directly via their earthing electrodes so as equip all installations supplied by the same LV network with voltage surge protectors During the period of lightening, (discharge current) it generate a field of Electric and magnetic component where radiation is received and forming appropriate aerial, which becomes induced current. Thus there makes a linkage between lightening conductor to the conductors in the structure. 2. 4. PROTECTION OF STRUCTURE FROM LIGHTNING A) External protection a. Passing the discharge current (during lightning) to earth. The main protection behind lightening effect can be protected by doing proper earthing . b. Uses of proper capture device may leads to protection of unshaped structural size (wider area), current density should be higher with probability of capture area. c. Some specific techniques such as shielding technique, Galvanic decoupling methods may be adopted to protect a total coverage area having different heights of tall building & Electric as well as magnetic effect . d. It is strongly recommended for buildings having many floors, that the lightning conductor, down conductor(s) is connected to the bonding systems on each floor to avoid a spark over through the walls of the building due to the voltage difference that occurs between the down conductors and the internal exposed conductive parts. The consequences in the installation of the effects caused by circulation of the lightning current in the down conductors can be minimized by: - Increasing the number of down conductors in order to divide the current and limit the effects caused - Ensuring that the down conductors are interconnected with the bonding systems on all floors in the building - Creating equipotential bonding systems incorporating all conductive elements e. Enhance the system in such a way that it must be must be capable of discharging the lightning current, avoiding a voltage rise in the earthing system itself and the surrounding ground. We must follow the scientific and objectively obtaining installation of voltage feedback points, to provide protection against high frequency voltage rise in the circuits interconnected with it. B) Internal protection a. Voltage surge protectors serve better rather than fuses and circuit breakers in case of protection towards electric and electronics equipment due to lightening from over voltage. b. Protect equipment against high-frequency interference, for which filters must be used. c. Protect an installation against the risks of temporary over voltages due to faults on the high or low voltage supply, such as neutral breaks. 5. CONCLUSION Due to complexity nature of lightning generation, an ample idea has been suggested in its transmission path, path of destruction (Short or long), fatal effect to man & animal, adverse effect in relation to its Structural view, mode of destruction, places for prone to lightening. The one and only one solution is a good lightning protection system helps to provide that path, thus reducing the probability that damage will occur to people or animals etc . REFERENCES [1] Golde, R.H., lightning protection, 1973 [2] IEEE standard 1100, IEEE Recommended practice for Powering And grounding sensitive electronic equipment (Emerald book). [3] National fire protection Association 780, Standard for the Installation of lightning protection systems, NFPA, 1997&2000. [4]Uman, Martin A and Krider, E. Philip,” Naturally and artificially Initiated lightning,” SCIENCE, 27 October 1989, volume 246 [5] Principle of lightning protection by Phillip R Tompson [6] Abdel-Salam, M. et al, Lightning Protection Using Energised, Franklin RodsAssiutUniversity, IEEE 1995. [7] Allen, N.L., On the Performance of Active and Passive Terminations in LightningProtection, University of Leeds. [8] Petrov, N.I. et al, Determination of the Striking Distanceof Lightning to EarthedStructures, University of WalesCollege of Cardiff, the Royal Society 1995. [9] Kunal Patel-- Protection Measures of Lightning Effect on Building [10] Power guide –A complete set of technical documents –Protection against lightning effect --R World Headquarters and International Department 87045 Limoges Cedex - France