Lightning rod

As a lightning rod means for protection of buildings is referred to lightning. With this the lightning rod part of the lightning protection system of a building dar.

Penetrates lightning into a house one, mostly produced considerable damage to property, because almost all electrical equipment and systems are destroyed. The high temperature (several 1000 ° C) there is a danger of fire.

A lightning rod is a guided up to an exposed place, grounded electrical conductor, which has a high electrical conductivity, thanks to its generous cross-section. He is said to derive the lightning current on the outside of the protected object along safely to the ground.

Function

A lightning protection system avoids primarily that lightning strikes in the protected building. The impact will instead be held in the lightning protection system. In the case of felling the lightning protection system provides the lightning current a defined, low-resistance current path, which damages are to be avoided on the protected object.

The actual lightning protection property is created by the peak effect and the low impedance of the grounded lightning rod:

• Through the lace effect is just above the top of the Ableitsystems a high electric field strength. The electric field strength reaches the breakdown field strength for air, this process can also be carried out in several steps such as corona discharge, the air is ionized in the immediate area and thus electrically conductive. This is the electrical discharge in the lightning rod. A lightning rod represents a termination system for atmospheric electrical discharge processes
• In addition, electrical charges always flow through the path of least electrical resistance, and the lightning conductor is usually a lower resistance than the rest of the building, - and is located closer to the source of the flash from the rest of the building.

Due to the good electrical conductivity of the lightning protection system, the space areas remain below or within the lightning protection system until shortly before discharge nearly field-free. For the determination of the shelter under a lightning rod the rolling sphere method is used, which is specified in IEC 62305-3: The radius of an imaginary sphere is limited by the bottom and the tips of the lightning protection system. The room area below the lightning protection device and outside of the rolling sphere is defined as shelter areas within the sphere represent Can available flash way dar. except the ground and the lightning protection system also touch to be protected parts of the building the imaginary sphere, is a lightning protection not given. In the rolling sphere method while four different protection classes are used: Class I is the highest requirement and Class IV the lowest.

For simple calculations, one starts from a capture range of 45 °. This means that everything that is at an angle of 45 ° below a fishing line or fishing rod of a lightning rod should be protected by this facility.

Lightning and electrical equipment

In electrical equipment, which are positioned in the vicinity of the lightning arrester, the strong formed by the flash electric and magnetic fields, however, can still cause damage by inducing currents and voltages in the lines of the device. The intensity of electric and magnetic fields will in the near field, ie under the assumption that the polluter is infinitely long ( which is the case near the flash), but linearly with the distance from the source, at a sufficient distance even with the square distance from the source decreases.

Even distant lightning strikes in or near power and communication networks ( telephone, cable TV, etc.) the devices can be dangerous in the house. For this purpose, various filters are offered that are designed to prevent the over voltage will damage the device in question.

History

As the inventor of the lightning rod is true Benjamin Franklin (1706-1790), who greatly interested in the 1740s for electricity. After his 1749 expressed theory flashes are nothing but sparks in a huge scale, he proposed in June 1752 before an experiment that resembles a lightning rod under construction. Franklin was in this perilous experiment in a summer thunderstorm a kite on a metal wire rising up and was able to show so that lightning represent electrical discharges. Regardless of Franklin recognized the Bohemian Premonstratensian Prokop Divis was the first in Europe, the principle and built in 1754 in his rectory garden in Přímětice Znojma a lightning rod. In Europe, especially Giambatista Beccaria had merit in Italy around the early spread of lightning rods.

In the early days of the lightning rod, it was felt that this applied not only at the highest point of the object to be protected, but also need to be especially acute. However, the shape of the highest point has no influence on the function. The first lightning rod in Germany was installed on the Hamburg Church of St. Jacobi in 1769. 1779 Lower Saxon university town Rinteln was surrounded with a wreath of seven freestanding lightning conductor rods that should protect completely the city. 1787 was built on the villa Lindengut in Winterthur, today the local museum of the city, the first lightning rod in Switzerland.

The lightning rod was however introduced relatively at the same time in many places in Germany, as reported by AT von Gersdorff in the Upper Lusatian provincial leaves of the design of a lightning rod in Upper Rengersdorf in the year 1772. This was part of the detailed description of the construction of a lightning rod for the tower of the castle Hainewalde which took place in 1782.

In southern Germany developed Johann Jakob Hemmer, Head of the Physics Cabinet at the court of the Elector Karl Theodor in Mannheim, " Hemmer 's five- pointed ." A lightning strike in the stables of Schwetzingen (1769 ) seems to have been the occasion that the famous polymath inhibitors also dealt with the need for lightning protection, and the five-pointed lightning rod, indicated by a vertical bar and a horizontal beams cross, invented and introduced. The first lightning rod inhibitor shear type was installed on 17 April 1776 the castle of Baron von Hacke in Tripp City / Pfalz. The further development was accelerated by a regulation of the Elector Karl Theodor, the particular 1776, that all castles and towers powder in the country are equipped with lightning rods. In the following years a further electricity swash spread in Germany, which led to the " inhibitor 's Five top " were in demand more and more. However, a benefit of the horizontal beams cross could never be proven. Therefore, the design was ultimately to no impact on the technical development of lightning protection.

A radioactive lightning rod was a particular execution of a lightning rod, in which a radioactive substance should ionize by their radiation, the air around the lightning rod tip and thereby deflect the flash on this. As a radioactive substance they contained typically enclosed alpha emitters ( radium -226 or americium -241 ) with a radioactivity of about 0.030 to 70 MBq per ray source. Several of these sources were mounted on a lightning rod. Radioactive lightning conductor with alpha emitters were so used, among other things, in western Switzerland, in France, under French influence in a number of countries, for example in Brazil and Spain. In Serbia and in all states of the former Yugoslavia gamma emitters and indeed 152Eu, 154Eu and 60Co were having an activity of about 4000 MBq to 20,000 MBq per radiation source is used with only one source of radiation per lightning rod was used. It has been shown, however, never in that the radioactivity improved efficacy. All lightning rods with radioactive sources are now dismantled for environmental reasons.