Induction effects: in a variable electroma-gnetic field, every conductor harnesses induced currentĮffects on a living being (human or animal): the passage of a transient current of a certain r.m.s value is sufficient to incur risks of electrocution by heart attack or respiratory failure, together with the risk of burns. They may result in deforma-tionsĮlectrochemical effects: these relatively minor effects are conveyed in the form of electrolytic decomposition through the application of Faradays law Thermal effect: heat generated by the Joule effect in the ionised channelĮlectrodynamic effects: these are the mechanical forces ap-plied to the conductors placed in a magnetic field created by the high voltage circulation. Wave (rise in pressure) originating in the discharge path this effect is perceptible up to a range of around 10 km Mechanism acoustic effects: caused by the propagation of a shock The effects of lightningThe effects of lightning are those of a high-strength impulse current that propagates initially in a gaseous environment (the atmosphere), and then in a solid, more or less conductive medium (the ground): visual effects (flash): caused by the Townsend avalanche In an average negative lightning stroke, the maximum current is around 35000A.ĪBB hlita lightning protection systems | 3
Helita lightning protection series#
The ascending jets then converge, producing a return stroke from the ground towards the cloud (the upward streamer) dur-ing which the electric current circulates: The convergence of these two phenomena produces the main discharge, which may be followed by a series of secondary discharges, passing unbroken along the channel ionised by the main discharge. The process is repeated until the tip of the last leader reaches a point a few dozen metres, or even just a few metres above ground level.
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A second leader then leaves the same point, follows the previous path at comparable speed, goes beyond the final point of the first leader by an approximately identical distance, then disappears in turn. Most lightning bolts exhibit the following phenomena: a leader leaves a point in the cloud and travels about 50 m at a very high speed of around 50000km/s. This can only be done with high-speed cameras.
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Mechanism of a lightning strokeIt is impossible to discern the individual phases of the light-ning stroke by simple visual observation. In practice, lightning strokes of the descending and negative type are by far the most frequent: it is estimated that on plains and in our temperate zones, they account for 96% of all cloud / ground discharges. LightningAccording to the direction in which the electrical discharge develops (downward or upward), and the polarity of the charges it develops (negative or positive), four classes of cloud-to-ground lightning stroke can be distinguished. Before and during the appearance of the lightning stroke, discharges can be seen both within the cloud and between clouds. The atmospheric electrical field on the ground, about 600V/m in fine weather is reversed and can reach an absolute value of 15 to 20kV/m when a ground discharge is imminent (the lightning stroke). Thus the cumulo-nimbus formation constitutes a sort of huge plate /ground capacitor whose median distance can often reach 1 to 2km. positive over the part of the ground nearby). Conse-quently, the lower part of the cloud causes the development of electrically opposite charges (i.e. In a typical storm cloud, the upper part, consisting of ice crystals, is normally positively charged, whilst the lower part, consisting of water droplets, is negatively charged.
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The existence of extreme temperature gradients in a cumulo-nim-bus (the temperature can drop to -65C at the top) generates very rapid ascending air currents, and results in the electrical energisation of the water particles. Its highly character-istic shape is often compared with the profile of an anvil of which it displays the upper and lower horizontal planes.
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This type of cloud is very extensive, both horizontally (about 10km in diameter) and vertically (up to 15km). StormsThe presence of unstable, moist and warm air masses gives rise to the formation of cumulo-nimbus storm clouds. Procedure for measuring the Early Streamer Emission of an ESEĪir terminal according to standard NF C 17-102 appendix C 10Įarly Streamer Emission Air Terminal - ESEAT 27Įxtension masts - Industrial chimney offset and bracket 31Ģ | ABB hlita lightning protection systems Hlita lightning protection systemsExternal lightning protectionĪBB hlita lightning protection systems | 1