Lightning-protection system

Under lightning protection encompasses measures against the harmful effects of lightning strikes to buildings.

Lightning strikes can destroy parts of buildings without lightning protection, if for example in building materials evaporate water contained or resin or essential oils explosively in wood or fires occur. The flash can couple directly or through its strong electromagnetic field in electric lines (eg, from antennas or photovoltaic systems ) or pipes (for example, solar collectors) and penetrate into the interior of buildings, potentially causing further destruction.

A complete lightning protection system consists of an outer and an inner lightning protection lightning protection (overvoltage protection).

• 4.1 -termination systems 4.1.1 rolling sphere method
• 4.1.2 Protective angle method
• 4.1.3 mesh method

Standardization

The comprehensive lightning protection is international european defined in EN 62305 in IEC 62305 and. In German-speaking EN was recorded with in accordance with the common rules of CEN / CENELEC by publication of an identical text with national foreword to the respective national standards.

The EN 62305 standard consists of four parts:

• Part 1: General principles
• Part 2: Risk management
• Part 3: Physical damage to structures and life hazard
• Part 4: Electrical and electronic systems within structures

The IEC 62305 was published in December 2010 in four parts. But the second part ( EN 62305-2 ) has not reached the required voting majority in Europe (but the IEC 62305-2 2010). Therefore, this part had to be reworked in CENELEC. Meanwhile became part 2 as DIN EN 62305-2; VDE 0185-305-2:2013-02 published.

In Germany the DIN EN 62305 was also because it contains security provisions on the prevention of danger to people, animals and things that added to the VDE rules and regulations under VDE 0185-305 with. It unfolds thus according to the prevailing law, the presumption to be an acknowledged rule of technology.

Function

A lightning protection system reduces the damage caused by a weft flash of lightning in the object to be protected. In the case of felling the lightning protection system provides the lightning current a defined, low-resistance current path. The primary protective function is passed out on the lightning current path object to be protected.

The protective effect of the capture device based on the fact that trained by the high edge field strength directly to the grounded capture device such as partial discharges, corona discharges. These weak gas discharges preferentially lead to electrically conductive tips and edges according to the peak discharge at the capture device to a partial ionization of the surrounding air, resulting in a possibly strikes in a row onset flash with higher probability in the capture device. Lightning protection systems are designed to increase the field strength over the edge of the lightning rod with a pointed end upwards as possible.

Means the concentration of charge carriers, which are oppositely charged to the electric charge of a cloud, the lightning strike is directed into the capture device.

Development of lightning protection systems

• About 1725-40 on the so-called Leaning Tower of Nevyansk ( Ural ) by Akinfiy Demidov
• 1752 Academy of Philadelphia and Pennsylvania State House, by Benjamin Franklin
• 1754 Přímětice / Prenditz near Znojmo / Znojmo, Monastery, by Prokop Divis OPraem
• 1760 Philadelphia, Home of Mr. West, by Benjamin Franklin
• 1733-1763 Dresden, Dresden Castle 1774 1 renewal
• 1765 Newbury (Berkshire ), Church
• 1766 Plymouth Lighthouse
• 1769 Żagań, Church, by Johann Ignatz of Felbinger
• 1769 Hamburg, St. Jacobi Church, by Johann Albert Heinrich Reimarus
• 1770 Vienna, Penzing, Church
• 1776 Trippstadter castle, first inhibitor shear Five Spitz - by Johann Jakob Hemmer
• 1779 Mannheim, Home
• 1779 Hamburg, St. Peter's Church
• 1780 Georg Christoph Lichtenberg in Göttingen
• 1782 Vienna, Narrenturm in the old General Hospital
• 1787 Winterthur, Villa Lindengut, now home to the Museum of the City, by Benjamin Franklin (the first lightning rod in Switzerland)

Secondary damage

Should a flash in spite of the lightning protection effect in the lightning protection system, so flow momentarily very high currents within the lightning rod. These high currents induce within the electrical supply cables ( mains, telephone lines, antenna cable, network cables, etc. ) of the protected object secondary voltages and secondary currents ( cf. transformer ) which electrical devices that are connected to this electrical lines, can destroy you. This effect occurs especially when the electrical supply lines near and parallel to the lightning rods are.

External lightning protection

The external lightning protection provides protection against lightning strikes that would take place directly in the plant to be protected. It consists of air-termination systems, drainage system and grounding system. In an idealized adopted building whose roof and exterior walls are made of metal or reinforced concrete, the external lightning protection could be executed as a Faraday cage.

Termination systems

The fishing facilities have to EN 62305 part 3, the task of direct lightning strikes, which would strike without the catcher in the building to capture. Termination systems can consist of rods, wires, ropes or metal parts to be protected plant such as pieces of metal roofs. The capture device surmounted by design, the outer contour of the actual building structure.

Your material must be weather-resistant, its good electrical conductivity and carrying lightning current. Therefore, metals such as copper, aluminum alloy ( AlMgSi), stainless steel (V2A) or galvanized steel be used. The cross section (usually 50 mm ²) or diameter (min. 8 mm) must be selected so that the high energy input of a lightning strike does not lead to melting of the arresting gear. It should also be borne in mind that the lightning current flows only a few milliseconds.

Exposed areas of a plant that are eligible for a direct lightning strike in question are often provided with safety devices or as a capture device. The termination systems are typically connected to each other and the shortest route to the discharge system.

Rolling sphere method

The rolling sphere method is a key method for the determination of entry points that are eligible for a direct lightning strike in question is standardized in EN 62305-3. It defines the endangered area as a lightning sphere whose center is the peak of the flash. The surface of the sphere represents an equipotential surface of an electric field dar. There are four lightning protection classes corresponding respectively to different probabilities that the peak value of the lightning current is below a predetermined current. The lightning protection class of an installation shall be determined on the basis of a risk assessment in accordance with EN 62305-2. For each lightning protection class a rolling sphere is defined with a given radius:

Experience has shown that a system that could be contacted by a sphere of such size, carried a lightning strike with appropriate lightning protection class anywhere. The smaller the radius of the rolling ball is believed the more potential impact points are detected.

The rolling sphere method can be applied by rolling a ball on a full scale model of the plant or with the help of geometry. Any lightning protection system must be able to withstand a full review after the rolling sphere method.

The empirically determined probabilities that a bolt of lightning strikes not in the installation to be protected, but is intercepted by constructed after the rolling sphere method fishing facilities, are:

For smaller lightning currents specified as the catch is less likely. The most comprehensive lightning protection is thus provided with lightning protection class I.

Protective angle method

The protective angle method is derived from the rolling sphere method simplified procedure, the limited regions defined by a calculated angle under termination systems, in which no direct lightning strike can take place. This angle is derived from tangents to a circle with the radius of the rolling sphere, and therefore on the level (upper end ) of the arresting gear above the reference plane dependent. About this angle can also be the required height of the capture device calculated.

Stitches method

The mesh is a method derived from the rolling sphere method simplified method that defines a network of lightning conductors to protect flat surfaces. The maximum mesh width depends on the required protection class.

In industrial process, the mesh is usually complemented by fishing rods, protect the components (for example air conditioners and roof domes ) that protrude through the mesh system.

Derivation system

The derivation system routes the lightning current from the catching equipment to the grounding system.

It consists of approximately perpendicularly out derivatives which are distributed over the periphery of the building. As derivatives of both lines separate and adequately dimensioned and carrying lightning currents associated metal parts can be used the system to be protected. The required number of discharges and their maximum distance depends on the required protection class.

Earthing system

The grounding system routes the lightning current into the ground.

Always contains the foundation earth, if it is present. He must have a run to the outside connection for each lead. If the foundation is completely isolated ( in old houses often lack the foundation earth ) or the earth resistance is too high, the foundation earth must be supplemented by additional ring earth, Strahlenerder, ground plate, ground rod or natural grounding. These must be permanently protected against corrosion and are therefore possible from stainless steel V4A material no. 1.4571 created. Only unaffected earth electrodes can be made of galvanized steel.

Ring earth, earth plates and Strahlenerder must be at least 50 cm deep placed in the ground. The depth prevents drying of the earth electrode in dry summers (increase of the grounding resistance ) and increased corrosion by air. Ground rod be driven vertically into the ground and can be quite nine feet or longer. They are usually made of stainless steel V4A, galvanized steel comes again when there is no risk of corrosion ( note electrochemical corrosion) only to be used there.

Internal lightning protection

Internal lightning protection is the set of measures against surge voltages of various kinds are also effects of a lightning strike to within 1.5 km distances and transferred to installations and electric and electronic equipment of the building.

These overvoltages may occur in several ways:

For overvoltage protection of electrical equipment and devices Surge protection devices ( Surge Protective Devices) are used, which are divided into three categories according to the standard EN 61643-11:

• SPD Type 1 ( coarse protection ) must be used on all entries of electrical wiring within the scope of the external lightning protection. They derive the full lightning current, but leave it at a dangerous for electronic devices overvoltage. The use of Kombiableitern (combined type 1 and type 2) may be more economical. The advantages lie in a space and cost savings, compared to a similar SPD type 1
• SPD Type 2 ( medium protection) to further reduce the voltage level. They are usually used in sub-distributions.
• SPD type 3 ( fine or device protection) reduce the voltage level to a safe level for electronic devices. They are close in as possible, max. 10 m, used in the terminals to be protected. SPD type 3, eg overvoltage protection sockets and surge protection socket adapter.

Lightning protection for antennas

Antennas are particularly at risk from lightning represents objects as they are functional reasons in a prominent position and are electrically conductive. If lightning strikes an antenna, the lightning current on the shield of the coaxial cable connected is led into the building. To avoid that then ignites in building an arc between the shield and grounded parts, each antenna is not in the scope of a catching device must be grounded. The high lightning current in the shield causes a high voltage on the cable, which destroys connected devices. This can be prevented by surge protection devices at both ends of the cable.

Self- Radiant masts for long and medium wave can not be grounded because of the ground which radiated RF energy would flow. Such masts have on Fußpunktisolator a radio link over which the flash can skip. This spark gap is adjusted so that when the applied voltage on the mast can not discharge occur even in heavy downpours. To promote skipping the flash over the radio path in addition, an inductor having one turn, the loop is incorporated in the flash feed line.

A monitored Verstimmschutz whether the antenna always has the correct resistance and results in a lightning strike, leading to the short circuit of the transmitter output, a brief switching off the transmitter. This prevents fed by the transmission power arcs remain, which may pollute the mast statics and the transmitter under certain circumstances. Sometimes even UV detectors are present, the monitor that no arcs remain. After a certain number of opening operations of the transmitter is often switched off for a long time and the mast is automatically grounded.

For the dimensioning of the isolation of Pardunenunterteilungsisolatoren is the static charge during storms the main criterion and not the transmission power. Since the insulators must be equipped with surge protectors that require maintenance always, the backstays are occasionally also on coils, which cause a detuning of the ropes, or grounded directly in exceptional cases. In such constructions, it is only on the mast and to the surge coils.

The details of the lightning protection controls in Germany the DIN EN 60728-11. Accordingly, all antenna systems must be equipped with a grounding conductor and a lightning protection, the grounding conductor must be connected to the equipotential bonding rail.

Exceptions apply to antenna systems, such as satellite antennas that are 2 m below the eaves edge and no more than 1.5 m from the wall mounted ausragend. This is usually the case when the antenna is mounted on the balcony or by a wall bracket below the eaves edge.

Lightning protection for overhead lines

Overhead lines for high voltage spans usually with earth wires. However, their effectiveness as a safety device can not be assessed because there is no recognized rules of technology for lightning protection of overhead lines. The International Electrotechnical Commission found several years ago, only that they are missing and should be formulated in the standard IEC 62305-5.

Lightning protection ropeways

Like all towers and overhead lines also run cable cars, especially cable cars, the risk of being struck by lightning. Should a flash in a cable car support directly into a gondola or in a support, train or a Rope, takes place a potential settlement with the ground. Cable car gondolas act like cars as Faraday cages, that is the interior remains in free approximation of the electric field (see also the operation of vehicles during a thunderstorm ).

Supports must be grounded in accordance with statutory regulations. When lightning strikes in one suspension cable, the lightning current is dissipated through the metal support rope saddles or bracing, with strikes in hoist ropes and pull ropes that run at the poles via rubber lined rollers, the current through the steel cables to the stations flows. You have technical components, especially sensors and other electrical and electronic components can be damaged by the lightning current, where the cables were not timely specially grounded before the approach of the storm.

The contact of the train or winding ropes with the roles and Seilumlenkscheiben not enough because of the rubber feeding from the same alone to ensure a low impedance path to ground. Although the rubber pads of rollers and deflection to avoid resulting in regular operation and thunderstorms electrostatic charging of electrically conductive material are produced, this limited conductive rubber material can not derive stronger lightning currents.

A positive contact is only possible with stationary ropes. In older systems, the cable car ropes are manually grounded with a firm grounding rod to be assembled before a thunderstorm, in modern systems can be fully automated. Generally reduce ground wires which are tensioned above the roadway from mast to mast, the risk of strikes in the Ropeway Ropes.

In steel cables single strands can be damaged at the lightning strike point. Although a lightning strike has so far brought no cable car cable directly to tear the cable car parts in the periodic rope inspections are visually inspected for possible damage from lightning strikes. Other effects of lightning strikes hit particularly exposed mounted anemometer and associated electrical lines ( and lines for electricity, telephone, speakers, data) without lightning rod nearby.

Lightning strikes in tows are very dangerous because of the potential equalization can be carried out by the bodies of more or less grounded lift users. Such investments would therefore be set according to the operating rules of thunderstorms out of service.