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LIGHTNING

lightning arrester

A is an instrument whose goal is not to attract lightning but repel desonizando air and lead the discharge to land, so as not to cause damage to buildings or people. This contraption was invented in 1753 by Benjamin Franklin while performing a series of experiments on the property that have sharp points, placed in contact with the ground, discharging electrified bodies located in the vicinity.

structure and functioning

arresters consist of a metal post (stainless steel, aluminum, copper or steel ) with a scanning head. The head can take many forms depending on their operating principle: it can be a point, multipoint, hemispherical or spherical and protrude above the highest parts of the building they protect. The head is connected to ground through a copper wire conductor. The ground spades is done by kneeling on the ground, by also buried conducting plates, or with a dip tube in water from a well). In principle, a lightning rod protects a theoretical area of \u200b\u200ba conical shape with the apex at the head, the radius of the zone of protection depends on the cone opening angle and in turn this depends on the type of protection.

The main objective of these systems is to reduce the damage they can cause a lightning strike on other elements such as buildings, trees or people, including the building itself is protected.

To understand how a lightning rod, summarizes how we present the high-voltage electric field, also called electric shadow.

Ray

is the electrical reaction caused by the saturation of electrostatic charges are generated and accumulate progressively in the clouds during the activation of electrical phenomenon a storm. When the potential difference between cloud and land value increases enough (about 10 ... 45 kV) electrostatic energy stored in the cloud is able to cross the little conductive atmosphere, and becomes a burst of energy electromagnetic (visible lightning and noise interference), acoustic energy (thunder), and finally, heat, a phenomenon that occurs in a fraction of a second.

The phenomenon represents random lightning between cloud-cloud, cloud to ground or ground-tag from an electric potential (10/45 kV) between two points or zones of influence of different polarity and different potential to offset loads. E

Effect tip:

loads around a conductor is not uniformly distributed but accumulate more sharp edges.

In this way, if you have a tip-shaped object under intense electrostatic field (as generated by a storm cloud), the accumulation of charges on the end is also very high.

Principle of lightning:

The lightning rod is nothing but a device that is placed on top of a building, direct the beam through a cable to land without causing damage.

We have already commented that the storm clouds typically have negatively charged base, while the area of \u200b\u200bland that lies below them, the effect of electrostatic induction, has a positive charge.

negative charges repel each other tag and are attracted by the positive charges of the earth.

Since the rod is grounded, electrons are repelled by the cloud with what is positively charged as the ground beneath the cloud.

due to the shape and characteristics arrester (tip effect), the charge density at the tip of the lightning rod is such that ionizes the surrounding air, so that the positively charged air particles are repelled by and attracted the lightning rod for the cloud, thus performing a double Objective:

1. on the one hand, there is an electric potential compensation these ions to be attracted to air by the cloud, partially neutralizing the charge. This will reduce the potential for cloud-land to levels below the 10000 V marking the boundary between dielectric behavior and the driver of the air, and thus prevent the formation beam.
2. other, lead to ground lightning offering a path of least resistance. This road will form the rod, the exhaust pipes and ground rods.

A phenomenon that we must consider is " natural dissipation, which is produced by trees, fences, rocks and other sharp objects form, whether natural or artificial, subject the electric field of the thundercloud, which will produce the equipotential naturally, producing charge neutralization of the cloud, or at the least, significantly reduced, thereby decreasing the risk to get the cloud over populated areas or dangerous.

lightning Types:

Whatever the form or technology used, all rays have the same purpose: to provide the beam path of least resistance to ground if traversing the structure the building.

There are two main types of lightning:

Lightning tip:

formed by a rod of 3 to 5 m long, galvanized steel 50 mm in diameter with the tip coated tungsten (to withstand the heat produced by impact with the beam). If you also want to prevent the formation of lightning can carry various air ionization devices.

-type
• Flanklin: based on the " point effect." is a typical lightning formed by a metal rod finished in one or more points.

The area protected by a lightning Flanklin classic is tapered.

Fig.

protected by a lightning Area classic.

In this type of lightning, the potential effect of compensation is very low, resulting in high risk areas are often used other types of conductors.

radioactive
• -type: it consists of a metal rod at whose end there is a box containing a small amount of radioactive isotope, whose purpose is to ionize the surrounding air by releasing particles alpha.

This generation of ionized air helps to ground lightning channel, obtaining a protected area of \u200b\u200bspherical-cylindrical shape.

Royal Decree 1428/86 of the Ministry of Industry and Energy prohibited specifically the use of this type of arrester.

Fig. area protected by a radioactive lightning rod

• solar corona ion Type: This type of arrester includes an electrical device for generating ions form permanent, and represents the best alternative to atomic lightning. The energy required for operation is typically from photocells.

• the piezoelectric-based on the ability of piezoelectric materials, to produce electrical charge from changes in its structure due to external pressures (such as those produced by the wind during a storm).

To improve the performance of the lightning rod tip, you can use a technique called " scattering matrix, which consists of a set of simple tips or ionizing whose mission is to offer many discharge point between land and cloud, and thus spread the neutralization download a larger region so as to reduce the appearance of points with different potentials that favor the appearance of lightning.

1. Lightning reticular or Faraday cage: consist of covering the building structure through a grounded metal mesh.

Fig. reticular area protected by lightning rods.

should be noted that modern buildings with steel structure, play a role similar to the Faraday cage, so the probability that a ray enters one of these buildings is extremely small.

Where it is necessary to place a lightning rod:

According Technology Standards Building is necessary to install lightning rods in the following cases:

buildings over 43 meters.

Places to handle toxic substances, radioactive, explosive or flammable.

Places with a risk index exceeding 27. This index is calculated depending on your geographic location, building materials and

TYPES LIGHTNING PROTECTION:

Yosra the protection of structures and individuals is necessary to use a system of lightning protection , which has mission to attract and channel lightning currents to the ground.
there are four systems used for protection from lightning.

PUNTA FRANKLIN Its mission is to bring the excitement of air on any point of the structure to be protected, creating an ionization effect of its edges, making downloading your area affects the coverage, and derive the lightning current to ground. The coverage of this head arrester is limited to a pyramid of protection of radio at the base, once half times its height.

"Tender" protection is formed by one or more drivers Aerio located on the structure to be protected. Drivers will be connected to ground through a downspout at each end. We The protected area is given by the area formed by all drivers air services.

FARADAY GAVI The system consists of reception beam through a set of tips absorbers are joined together by a wire conductor forming a mesh large. This grid will be connected to ground through a network of wires.

ESE LIGHTNING (PDC) The PDC emit electrical discharges of lightning reverse polarity, resulting in the attraction of lightning, and raising the point of impact above the structure we are protecting. This will get a larger coverage radius at the base with respect to a conventional lightning rod. PDC A tip is not comparable to a Franklin rod, if not a group of them. This affects an economic benefit in the time of installation. When a lightning approaches land, it creates a download on any elevated. In the case of a passive protection system, such as a Franklin rod, only captures the downloads you can receive the tip of ionization itself. PDC head creates an easy path to discharge ensuring greater efficiency for the capture of lightning. Thanks to its prime device emits a high voltage signal amplitude and frequency determined and controlled. Ensures effectiveness through the rapid formation of the upward that spreads continuously until the downward beam, bringing the point of impact of the discharge well above the protected structure. Do to raise the impact point, automatically extend the radius of a lightning rod protection against conventional.

CERTIFICATES Nimbus PDC heads are contempldots with current standards UNE 21186 and NF C 17-102 French.

THE SURGE: download rays on any cable driver data or power transmission, causing transient currents, characterized by its short duration, rapid growth and very high peak values \u200b\u200b(up to several tens of kW.). download a beam propagating in a radius of several kilometers, and its spread to the ground, raises the potential, inducing strong surge in buried cables and increasing tensions grounded. In an electrical installation, all drivers who come from abroad, are likely to pave the way for the surge, causing damage to all connected devices or systems. surges caused by atmospheric phenomena reach the facilities in three different ways: The beam can fall directly on the airlines, the surge propagating along several kilometers. The surge ends up deriving the user and ground through their computers, causing damage or total destruction. radiation issued by the lightning strike with an object (eg lamppost, tree, lightning ...) next to power lines, telephone, data ... induced transients, leading them through the network within our facilities, causing damage or destruction of equipment connected. When lightning strikes the ground directly or through a grounded structure, the current of the lightning discharge can increase the potential of land to several thousand volts as result of the current in the field.

SURGE PROTECTION:

When a voltage on a line, it runs a current of about Ka. To avoid overvoltage
equipment connected to the line, has dew install a protector, which will lead to ground, the intensity generated by the surge without concerns him.
A guard acts as a voltage controlled switch. If the voltage is larger than nominal line to protect, guard goes low impedance earthed. In normal operation the protector is in high impedance and is transparent to the installation.

ideal protector, should derive all the maximum intensity generated by the surge, and ends the residual stress should be smaller, that borne by the protected equipment. In practice there is no protector that meets these two criteria.

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achieve a high discharge power and low value of residual stress in a single protector is impossible, so the use of a single guard does not ensure total protection of the facility where sensitive electrical devices. For this reason we installed two or more levels of protection, phased and coordinated.
A first level will be a guard with a high discharge power (65 Ka/40Ka). The second (up to a third level in some cases) will be protective of low residual stress, below the cost to the protected devices. These guards are fitted as close as possible to protect equipment.

telephone lines, whether voice, and data, analog or digital, are highly exposed to lightning overvoltages suffering, having most outside the network, by air. Also radio antennas tickets or information networks are vulnerable to surges induced by lightning.
Unlike the energy networks, to protect the transmission lines (telephone, radio ...), install a single level of protection, as do several steps we cause the loss of signal. These protections will be connected to the serial installation. In case of failure of an overvoltage protection, the line should be no continuity.

conditions.