9.5 Lightning and surge protection for cable networks and antennas for TV, sound signals and interactive services

Transcription

1 9.5 Lightning and surge protection for cable networks and antennas for TV, sound signals and interactive services IEC 6078-: 005 complies with the state of the art and offers easy, standardised and effective protective mechanisms against the effects of lightning strikes into antennas. Antennas installed according to this standard do not increase the probability of lightnings to strike the object under consideration. Nor is an antenna system installed according to this standard a substitute for a lightning protection system of a building or structure. This standard deals with the safety requirements for stationary systems and devices and is, if applicable, also valid for mobile and temporary systems (e.g. campers, recreational vehicles). The range of validity comprises cable TV networks (CATV networks) and satellite community antenna television systems as well as individual receiving networks. Outside antennas which are installed at a level of more than m below the roofing or the roof-edge and at distance of less than.5 m from the building (Figure 9.5.) as well as antenna systems inside a building are excepted from the following measures. However, at least the of the coaxial cable shields to an is urgently recommended. All interconnected, conductive and touchable components of the installation should be integrated into the bonding as well. Antennas must not be installed on buildings with easily inflammable roofing (e.g. thatch or similar materials). Antenna cables and ing conductors must not lead through those sections of rooms where easily inflammable materials like hay, straw or alike are stored, or in which there is a potential risk of explosive atmosphere to arise. An has to be mechanically solid with a copper cross section of minimum 4 mm. The shields of the coaxial cables going in or out of the building have to be connected with an and by the shortest route with a common. An ing conductor being capable of carrying lightning current can be a single solid wire having a minimum cross section of 6 mm of insulated or bare copper, or of insulated 5 mm aluminium or of 50 mm aluminium wrought alloy (not to be directly installed on or in plaster nor on or in concrete), or of steel 50 mm, preferably for external installation. Fig min. m max..5 m Horizontal and vertical distances of antenna arrangements requiring no ing Natural components which can be used, are for example, the frame of the building or structure, the interconnected reinforcement steel of the building or structure, facades, railings and substructures of facades, provided that their dimensions meet the requirements of down-conductor systems and their thickness is not less than 0.5 mm, their electrical conductivity in vertical direction is ensured (these permanent s have to be carried out by brazing, welding, pressing, screwing or riveting), or that the distance between structures does not exceed mm and the overlapping of two structural elements is at least 00 cm. IEC 605- does no longer stipulate this possibility of overlapping sheet, except the substructure is continuously conductive in vertical direction. If not, the overlapping sheet 50 LIGHTNING PROTECTION GUIDE

2 m 0.5 m foundation electrode α > 60.5 m flat shaped electrode α.5 m m.5 m rod ing m.5 m m.5 m rod building foundation steel skeleton, reinforced concrete buildings Fig Examples of permitted electrodes s have to be safely interconnected according to the requirements of IEC Attention: Forming of loops has to be avoided. The -termination system has to be designed according to one of the following manners (Figure 9.5.): Connection with the external lightning protection system of the building or structure. Connection with the -termination system of the building or structure. Connection with at least two horizontal electrodes having a minimum length of.5 m, being installed in an angle > 60, at least 0.5 m deep and not closer than m to the foundation, or connected with one vertical or slanted electrode not shorter than.5 m or two vertical electrodes not shorter than.5 m, installed at a distance of m from each other and not closer than m to the foundation. Minimum cross section of each electrode to be 50 mm copper or 80 mm steel. Natural components such as interconnected reinforcement of concrete or other suitable underground constructions embedded into the foundation of the building the dimensions of which complying with the above limit values, can be used as well. Other -termination system according to IEC 605- are also permitted. If a supplementary electrode is installed adjacent to the LIGHTNING PROTECTION GUIDE 5

3 ing conductor 6 mm Cu DEHNiso Distance Holder e.g. with pipe clamp Part No protective angle highly insulating distance holder without mains Fig Earthing and bonding of antennas on buildings without external lightning protection system Fig Antenna with air-termination rod and highly insulating distance holder on pitched roofs with external lightning protection system bonding Potentialausgleichsleiter conductor protective angle of isolated airtermination system to external lightning protection system Air-termination rod, e.g. 500 mm Part No Concrete base, e.g. 7 kg Part No s Fig Antenna with air-termination rod on a flat roof of buildings with external lightning protection system termination system of the building, the electrodes have to be interconnected. In case of buildings without lightning protection system (LPS), the mast with an ing conductor has to be connected by the shortest route with the electrode. The ing conductor has to be installed straightly and vertically. The coaxial cable shields have to be connected with the mast by s (Figure 9.5.). In case of buildings with lightning protection system (LPS), the antennas preferably shall be installed within the protective range of an air-termination system, which means in the range of DEHNgate DGA FF TV DEHNflex DFL M 55 Part No Part No Fig Surge protective devices downstream the for the coaxial cable shields in case of antenna systems with external lightning protection system and isolated air-termination system 5 LIGHTNING PROTECTION GUIDE existing protective zones or by isolated air-termination systems. Only if this is not possible, a direct with the external lightning protection system shall be implemented. In this case the ariswww.dehn.de

4 ing conductor 6 mm Cu ing conductor 6 mm Cu combined lightning current and DEHNgate DGA FF TV Part No DEHNflex DFL M 55 Part No DEHNgate DGA GFF TV Part No DEHNgate DGA FF TV Part No DEHNflex DFL M 55 Part No Fig Surge protective devices downstream the for the coaxial cable shields in case of antenna systems without external lightning protection system and with isolated air-termination system Fig Combined lightning current and s downstream the for the coaxial cable shields in case of antenna systems without external lightning protection system ing partial lightning currents via the coaxial conductors have to be taken into account individually. Lightning bonding has to be performed for the conductors going into the building. If an antenna is protected by isolated air-termination systems it means that in the area of flat roofs an air-termination rod will be installed with the required separation distance s, putting the whole antenna arrangement (mast and antennas) in the protective zone of the protective angle (Figure 9.5.4). Now the antenna arrangement is no longer in lightning protection zone LPZ 0 A (risk of direct lightning currents) but lightning protection zone LPZ 0 B (risk of indirect impulse currents and of the unattenuated electromagnetic field of lightning. that in the area of pitched roofs an air-termination rod will be installed with the required separation distance s using highly insulating distance holders (DEHNiso distance holders) to fix it at the antenna mast, putting the whole antenna arrangement (mast and antenna) into the protective zone of the protective angle (according to the applicable class of LPS) (Figure 9.5.5). Also here the antenna arrangement is no longer in lightning protection zone LPZ 0 A (risk of direct lightning currents), but in lightning protection zone LPZ 0 B (risk of indirect impulse currents and of the unattenuated electromagnetic field of lightning). Protection against surges, irrespective of an installed isolated air-termination system, has to be provided for the coaxial cable shields by surge protective devices, to be installed downstream the (Figure 9.5.6). These surge protective devices to be used both as single devices and for rail mounting protect the downstream devices against inductive and/ or capacitive inputs of waveform 8/0 μs, arising from cloud/ cloud flashes, distant strikes or direct strikes into the isolated air-termination system. Surge protective devices Type have to be provided for any electrical equipment with 0/50 Hz downstream the, which LIGHTNING PROTECTION GUIDE 5

5 combined lightning current and... junction box amplifier terminal block DEHNgate DGA GFF TV Part No DEHNgate DGA FF TV Part No DEHNflex DFL M 55 Part No equiptential Fig Combined lightning current and s downstream the for the coaxial cable shields in case of underground cable networks is installed for the coaxial cable shields. Care has to be taken that the lightning bonding is carried out for all systems leading into the building. A lightning protection system not being installed, the following is recommended: An air-termination rod mounted with insulated distance holders prevents from a direct strike to the antenna. For this the air-termination rod has to be connected with the electrode by a separately installed ing conductor (Figure 9.5.7) to be guided preferably on the outside of the building and to be connected with the electrode at ground level. Antenna mast and bonding bar have to be connected with the electrode via an. If the antenna mast is ed directly, combined lightning current and s have to be provided (Figure 9.5.8), because partial lightning currents, which the surge arresters are not able to control, will be conducted in this case through the coaxial cables. The antenna mast has to be connected with the electrode by an ing conductor. Underground utility lines of systems require combined lightning current and s being able to carry lightning currents. They also have to be mounted near the point of entrance into the building (Figure 9.5.9). 54 LIGHTNING PROTECTION GUIDE