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Lightning, Lightning Protection and test Standards
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... It is installed on a geometrical structure provided with earth wire and a ground electrode. The Franklin rod receives the lightning flashes directly or indirectly by induced effect and it discharges them to the ground so the building is safe [15][16][17]. ...
... The building structures used for experiments and simulation were scaled down and were tested in Malaysian ambient weather conditions. The Lightning Air Terminals (LATs) were installed on selected shapes according to American standard NFPA 780 [15]. Scaling of the building structures was performed according to [28][29][30][31]. ...
In this paper, upward leader initiation and the probability of lightning flashes on different air terminal were analyzed in detail. With the growing global warming, lightning flash density has increased abruptly, especially in tropical countries. Upward leaders are the critical elements to be considered for defining comprehensive protective measures against lightning during thunderstorms. This article presents the lightning flashover phenomenon on scaled buildings with installed lightning rods. Moreover, the electric field and initialization of upward leaders from Lightning Air Terminals (LATs) were analyzed in detail using Ansys Maxwell as a simulation tool. For the experimental work, a high-voltage impulse generator was used. The air gap between the lightning rods and the top electrode was kept constant in all scaled structures. The purpose of using an identical air gap was to study the upward leader and its electric field for all structures. The effects of the upward leaders on the electric field plots are explained in detail and allowed the determination of the electric field’s intensity around each air terminal for the provided air gap between the tip of the rod and the top electrode. A low-cost lightning protection system was taken into account, as the economic crisis is worsening with time. A Franklin rod was used as the primary protection device for the initiation of the upward streamer. The experimental results were obtained in Malaysian weather conditions based on standard values of temperature and pressure. The study presented in this article shows that based on the experimental work, field plots were obtained for both the air insulation scenario and the condition when the upward leader was incepted. The simulation results showed a firm agreement with the measured values. Similarly, by upward leader inception, the strikes could be predicted accurately on every installed air terminal.
... Because of the involvement of the grounded metal poles, the telephone network of the houses and the power wiring in those houses, the charge collection and dissipation efficiency was very high. Metal objects on ground are known to become instrumental in causing high lightning currents [14]. The cable inside the poles was found burnt and broken. ...
Cloud to ground lightning causes damage to objects and injures people by different mechanisms like direct hit, contact voltage, side flash, step voltage etc. Understanding the different ways of involvement of objects and personnel in lightning disasters is helpful in deciding the type and level of external protection. Details of investigations conducted in 47 lightning disasters spread over several years are presented. The different types of mechanisms of involvement of objects and personnel in these incidents are discussed. All the incidents investigated were from Kerala, India which is a region of relatively high vegetation density. In 51% of the cases objects and personnel were found to have got involved by ground conduction of lightning energy into dwellings. Some of the cases of ground conduction involvements are unusual. The high degree of damage in some of the unusual cases is attributed to the continuing current component. The role of metal objects in charge collection and dissipation is also discussed. The relative importance of ring conductor to the lightning conductor in places of high vegetation density is brought out.
Eine Abschätzung der im Gewitter zum Umsatz kommenden Energiebeträge zeigt, daß die in den elektrischen Phänomenen verbrauchte Energie im Gesamt-Energie-Umsatz nicht ins Gewicht fällt. Zieht man jedoch den Vergleich nur zu dem Teilbetrag des mechanisch-thermodynamischen Energieumsatzes, der sich über den normalen Energie-Umsatz des Wetter- bezw. Austauschgeschehens erhebt, und nimmt versuchsweise für diesen den aus dem Niederschlag allein abgeleiteten Betrag an, so ergibt sich, daß die elektrischen Phänomene etwa 1/4 dieses Betrages beanspruchen. — Die Abschätzung des elektrischen Energie-Umsatzes erlaubt es, die mittlere in einem Erdblitz umgesetzte Energie abzuleiten: Sie ergibt sich zu rund 2000 kWh. Eine noch nicht lösbare Diskrepanz ergibt sich für die Feldstärke unterhalb der Gewitterwolken.
Summary
By an estimate of the energy budget of the thunderstorm is shown that the energy of electrical activity is entirely negligible in considerations of the whole budget. But if the energy of electrical activity is only compared with that amount of the whole energy which exceeds the normal energy amount of the «Austausch» it can by shown that the electrical phenomena need about 1/4 of this amount (this amount is estimated only from the precipitation). — By the estimation of the electrical energy budget it is possible to give the mean energy of a lightning: about 2000 kWh. In considerations of the potential-gradient under thunderstorm clouds a contradiction is given which can not be solved until now.
On or before June, 1751, Benjamin Franklin and co-workers showed that gunpowder could be ignited by a small electric spark, and subsequently people used gunpowder to enhance the explosions of "thunder houses" to demonstrate that grounded metallic rods would protect model structures against lightning damage. Even before the sentry box and kite experiments proved that thunderclouds are electrified and that lightning is an electrical discharge in 1752, Franklin had hypothesized that a tall, well-grounded conductor might reduce or prevent lightning damage by silently discharging the cloud, and if a discharge did occur, then the tall rod would offer a preferred place for the lightning to strike, and the grounding conductors would guide the current into the ground in a harmless fashion. Over the next 10 years, experience gained through practice showed that grounded rods did indeed protect ordinary structures from lightning damage, but a question remained about the best way to protect gunpowder magazines. In 1762, Franklin recommended a tall "mast not far from it, which may reach 15 or 20 feet above the top of it, with a thick iron rod in one piece fastened to it, pointed at the highest end, and reaching down through the earth till it comes to water," and in 1772 he made a similar recommendation for protecting the British powder magazine at Purfleet. In 1780, Jan Ingenhousz asked Franklin to "communicate to me some short hints, which may occur to you about the most convenient manner of constructing gun powder magazines, the manner of preserving the powder from moisture and securing the building in the best manner from the effects of lightning." In his reply, Franklin detailed a method of protection that is almost perfect, "they should be constructed in the Ground; that the Walls should be lin'd with Lead, the Floor Lead, all 1/4 Inch thick & the Joints well solder'd; the Cover Copper; with a little Scuttle to enter, the whole in the Form of a Canister for Tea. If the Edges of the Cover scuttle fall into a Copper Channel containing Mercury, not the smallest Particle of Air or Moisture can enter to the Powder, even tho' the Walls stood in Water, or the whole was under Water." In 1876, the Scottish physicist, James Clerk Maxwell, made almost exactly the same recommendation for protecting against lightning, a method known today as a "Faraday cage."
The first wideband dE/dt recordings have been obtained for the narrow bipolar pulses previously identified by Le Vine (1980) as sources of the strongest RF radiation from lightning. These dE/dt waveforms are dramatically different from those of other known lightning processes. A burst of high-frequency noise is superimposed on the slower bipolar pattern that might be expected from the relatively smooth E waveforms. For 18 such pulses from an isolated thunderstorm cell at known range, the mean E and dE/dt, rnage-normalized to 100 km, were 8.0 + or - 5.3 V/m and 20 + or - 15 V/m/microsecond respectively. Spectral analysis indicates that the sources of these pulses radiate much more strongly than first-return strokes at frequencies from 10 MHz to at least 50 MHz. Absolutely calibrated power and energy spectra are presented which are reliable from 200 KHz to perhaps 20 MHz. At 18 MHz the narrow pulses appear to contain nearly 16 dB more spectral energy than first return-stroke waveforms from the same range. Supporting evidence shows that they generally occur as isolated pulses in intracloud flashes but not associated with K changes or other known phenomena. They can occur in either polarity.
Forty-two years of lightning casualty and damage reports in Colorado are summarized. The data are from NOAA's Storm Data, which is compiled monthly by the US National Weather Service. The dataset contains 103 deaths, 299 injuries, and 191 damage reports from 1950 through 1991. Houses were the most common objects reported as damaged by lightning. Fire was the most common source of lightning damage. Comparisons are made of these with previous studies of lightning in other locations around the world. Geographical patterns of lightning incidents for the state are shown in maps of total number of casualties, and number of casualties normalized by population density for each county. Higher casualty rates per population and area occur over the mountains and some areas of the eastern slopes than elsewhere. People involved in recreation or employment were more likely to become lightning victims. Outdoor recreation casualties were most frequent in the mountains, agricultural cases over the eastern plains, and sports and domestic casualties along the urban corridor east of the mountains. Year-to-year variability was high in all categories. Ranch and farm casualties decreased greatly after the early 1960s. Outdoor recreation, urban, and work cases steadily increased over the entire period in accordance with the population increase. However, sports casualties increased at a substantially larger rate than would be expected from the population increase. Statewide lightning victim counts by 5-yr periods correlate well with statewide summertime temperature, but not as well with precipitation. -from Authors
A physical model of initiation of lightning flashes by aircraft in thunderstorms, based on the ``bi-directional, uncharged leader'' concept of Kasemir, is verified with airborne data from lightning strikes to instrumented airplanes (NASA F-106B and FAA CV-580). Characteristics of electromagnetic processes during lightning attachment to aircraft are identified with those in negative stepped leaders and positive leaders in natural lightning, in flashes triggered by wire-trailing rockets, and in laboratory discharges. It is shown that (1) a triggered flash starts on aircraft with either a negative corona or a positive leader that depends on the ambient electric field vector and the vehicle form factors; (2) the positive leader with continuous current that increases with time to the level of several hundred amperes is followed in a few milliseconds by the negative stepped leader with current pulses of a few kiloamperes; and (3) the two leaders develop in space simultaneously and bi-directionally from the oppositely charged extremities of the airplane.
The analysis of airborne electromagnetic records of seven lightning strikes to the FAA CV-580 instrumented airplane during the 1987 field campaign and eleven strikes to the French C-160 airplane during the 1988 Tranasll campaign was aimed at revealing and interpreting processes taking place during the intracloud propagation of lightning strikes initiated on or intercepted by the airplane. It is shown that intracloud development of the strike may consist of recoil streamers, dart leader/return stroke sequences, and the secondary initiations of new discharges. These processes, with their high current-pulse amplitudes, may present greater threat to aircraft than current pulses during strike initiation. The latter are presently considered by the technical community to be the primary lightning threat to aircraft.
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Measurements of the electric field E and dE/dt signatures radiated by first return strokes striking seawater in 1985 show that the average peak E and peak dE/dt are 8.6+/-4.4Vm-1 and 42+/-13Vm-1mus-1, range-normalized to 100 km, after correcting for the effects of propagation. The full width at half maximum of the initial half-cycle of dE/dt is 64+/-22ns. The corresponding peak current and peak dI/dt, inferred using a simple semiempirical relationship, are 29+/-15kA and 105+/-34kAmus-1. These results are in good agreement with similar measurements made in 1984.
within a few tens of kilometers to the east over the Atlantic Ocean. Biases that are introduced by a finite threshold in the triggered recording system were kept to a minimum by triggering this system on the output of a wideband RF receiver tuned to 5 MHz. Values of the peak dE/dr during the initial onset of 63 first strokes were found to be normally distributed with a mean and standard deviation of 39 _+ 11 V m- /xs - after they were normalized to a range of 100 km using an inverse distance relation. Values of the full width at half maximum (FWHM) of the initial half-cycle of dE/dr in 61 first strokes had a mean and standard deviation of 100 +_ 20 ns and were approximately Gaussian. When these results are interpreted using the simple transmission line model, after correcting for the effects of propagation over 35 km of seawater, the average value of the maximum current derivative, (dI/dt)p, and its standard deviation are inferred to be 115 + 32 kA/s -, with a systematic uncertainty of about 30%. The FWHM after correction for propagation is about 75 +_ 15 ns. The inferred values of (dI/dt)p are significantly higher than most previous measurements of natural first strokes during direct strikes to instrumented towers but are in good agreement with direct measurements of dI/dt during subsequent return strokes in rocket-triggered discharges in Florida.