Comprehensive lightning protection technology for buildings and its application?

What is the specific content of comprehensive lightning protection technology and its application in buildings? Zhong Da Consulting will answer your questions below.

Lightning strike is a natural phenomenon, and its great energy is well known. For centuries, human beings have formed a set of mature theories on the research, exploration and preventive measures of lightning damage. From the perspective of EMC (electromagnetic compatibility), lightning protection can be divided into multi-level protection zones from the outside to the inside. The outermost layer is level 0, which is a direct lightning strike area with the highest risk. Mainly protected by external (building) lightning protection system, the deeper the risk, the lower. The interface division of protected areas is mainly composed of lightning protection system, reinforced concrete and shielding layer composed of metal pipes. From the 0-level protection zone to the innermost protection zone, multi-level protection must be implemented to reduce the overvoltage to the level that the equipment can bear. Generally speaking, about 50% of lightning will directly leak into the earth after passing through traditional lightning protection devices, and 50% will flow into electrical channels on average.

The general lightning protection principle is:

1. Lead most lightning current directly to underground leakage (external protection);

2. Blocking overvoltage waves introduced along power lines or data and signal lines (internal protection and overvoltage protection);

3. Limit the amplitude of surge overvoltage on the protected equipment (overvoltage protection).

These three lines of defense cooperate with each other, perform their duties and are indispensable.

First, the application of comprehensive lightning protection technology for buildings

(1) Railway yard

The key areas of direct lightning protection in railway stations and yards are communication building, signal building and outdoor fork throat equipment.

1. Direct lightning protection of communication buildings

Using a microwave tower about 45 meters high near the communication building, IF3 lightning rod is installed at the top of the tower, and the installation height of the lightning rod is 2.5 meters higher than the top of the tower. After calculation, the protection radius of lightning rod to the ground can reach 1 19 meters. The down conductor shall be galvanized flat steel with a cross section greater than 1 2 mm× 4 mm. The grounding resistance of the lightning protection grounding device shall be less than1ohm.

2. Direct lightning protection of signal building

Using the signal building of the protected building, the height is about10m, and the IF3 lightning rod is installed at the top of the signal building, and the installation height of the pin exceeds the roof by 5m. After calculation, the protection radius can reach 109 m. The roof is embedded with 350mm×350mm× 10mm thick steel plate, which is convenient for welding the lightning rod base. Weld two down leads in the opposite direction from the base, and lead them underground with round steel greater than 8mm along the external wall of the building, and connect them with the grounding ring of the building. The grounding resistance of the lightning protection grounding device is less than 1 ohm, and the lightning rod is connected with the grounding device.

3. Direct lightning protection in outdoor bifurcation throat area

The throat area of railway station bifurcation group has the characteristics of centralized equipment distribution. The length of throat area in bifurcation group is about 145 meters. There is a12m-high iron tower near the throat area of the bifurcation group, and IF3 lightning rod is installed at the top of the tower. After calculation, the protection radius can reach111m. The down conductor shall be galvanized flat steel with a section greater than12 mm× 4 mm. The grounding resistance of the lightning protection grounding device shall be less than10Ω.

(2) Civil airports

The design and construction of lightning protection and lightning protection electromagnetic pulse and internal overvoltage in civil airports should not only reliably design lightning protection devices outside the building, but also consider a large number of electronic information equipment inside the building to improve the protection against lightning electromagnetic pulse and internal overvoltage. Some key points in the design are discussed below.

1. External lightning protection system

In the airport, the lightning receptors of the first and second lightning protection buildings are mainly composed of ordinary needles, belts and nets. If the building itself can't implement ordinary lightning protection measures, it can adopt advanced foreign E.S.E lightning rod. When designing the external lightning protection system of lightning protection buildings, total equipotential connection and common grounding should be realized. Considering the practical application effect, the downlead can be checked point by point by using the welded steel downlead in the main load-bearing column.

2. Design of lightning protection electromagnetic pulse and internal overvoltage protection for buildings.

Special attention should be paid to the protection of lightning electromagnetic pulse introduced by low-voltage cables. According to GB50057.94 Code for Lightning Protection Design of Buildings and IEC 6131General Principles for Design of Lightning Protection Electromagnetic Pulse, as well as relevant national and industrial standards, for Class I electrical equipment with a large number of electronic equipment (PE wires are introduced), according to IEC 668,

Second, the application of lightning protection technology in forecasting work

Hydrological forecasting system

Hydrological flood forecast is carried out within the specified time, and there is no choice in time. In the site where the hydrological cableway is erected, the main cable and working cable of the cableway are all made of steel, which is a conductor and vulnerable to lightning. In order not to affect the hydrological test, the ropeway must be equipped with lightning protection facilities.

1. Lightning protection of hydrological cableway facilities

The span of hydrological cableway is small, so lightning rod can be used for lightning protection; When the span is large, the lightning rod can not take into account the full-span ropeway, so the lightning rod is used for lightning protection. A lightning tower with a height of more than 3m is erected at the upper end of the main pole of the cable way, and then a lightning conductor is installed in the lightning tower, so that the lightning conductor and the steel support are connected with the grounding grid by flat steel. The lightning rod is required to be galvanized steel strand with a cross-sectional area of not less than 35m㎡；; Round steel with a diameter of not less than 8mm is preferred for down lead, and the resistance of grounding grid is not more than 4Ω. The protection of ropeway induced lightning mainly depends on measures such as power supply lightning protection, signal lightning protection and reasonable grounding network laying, which can reduce or eliminate the influence of induced lightning. Most hydrological stations in the Upstream Bureau of Hydrology Bureau of Yangtze River Committee adopt 3 ~ 5m high lightning protection towers at the upper ends of steel supports on the left and right banks, install lightning protection wires and connect them with the ground network, which has obvious lightning protection effect.

2. Lightning protection of water level and rainfall instruments

Lightning protection system with lightning rod, down lead and grounding grid is adopted to prevent water level and rainfall instruments from being directly struck by lightning. Because the observation of water level and rainfall is carried out in the field, the observation equipment; Rainfall pipes, satellite antennas and solar panels are all installed at the top of the self-recording well (the maximum diameter at the top of the self-recording well is less than 2m), so the lightning rod can only be installed at the top of the self-recording well. If the height of the satellite antenna is 1.0m and the height of the lightning rod is 2.7m, the antenna can be placed in the effective protection range with the lightning rod as the center and a radius of about 3m (the protection angle of the lightning rod is calculated as 60, and the lightning rod should be installed in the northeast of the maritime satellite antenna, because the southwest is the landing direction of the satellite).

In order to avoid the induction lightning of the power line to the instrument, the solar battery is used to supply power by floating charge. The signal line of water level and rainfall information transmission adopts shielded wire, which is introduced into the flood forecasting station from underground through PVC sleeve. The flood forecasting station transmits the water level and rainfall information to the hydrological sub-center through PSTN or network, and the flood forecasting station can also pass through the standby channel. Maritime satellite (or Beidou satellite) sends water level and rainfall information directly to hydrological sub-center.

3. Lightning protection system of hydrological sub-center

Water information sub-centers are generally built in large and medium-sized cities. The geographical and geological conditions make it more difficult to lay the grounding network, but the distance between the lightning rod and the satellite antenna and the solar panel is arranged in strict accordance with the requirements of the 60-degree protection angle.

(2) Weather radar

The construction of weather forecast system radar should also consider lightning protection. Scientists have applied special comprehensive lightning protection technology in the construction of a new generation weather radar in Simao, and reported and analyzed the specific design work.

1. Lightning connection

Using lightning rods and combined protection: four FRP lightning rods with the same height of 10m are installed at the top of the radar detection building with equal circumference and equal spacing from the outer edge of the radome, and a lightning rod with an overhead height of 3.5m is installed along the top of the roof parapet, so that the radar antenna and the building are jointly protected by lightning rods and direct lightning.

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A metal shielding grid of 150cm× 150cm is laid along the walls and window frames around the machine room to "enclose" the electrical equipment in the machine room, and the exposed conductive parts of various equipment are properly grounded, so that the indoor radar equipment is in the first, second and third shielding protection zones.

3. Balanced connection

The method adopted is: from the foundation of the building, the metal components at the same level, at the same entrance and at the junction of the lightning protection area are connected with equal potential layer by layer to form an equipotential connection network. Equalizing wiring is a complicated work and one of the main factors to judge the quality of lightning protection design and construction.

4. Overvoltage protection

The protection adopts voltage switching type and voltage limiting type surge protectors. The power supply system adopts three-level protection; SPD 1 is installed on the main distribution box of transformer low-voltage side power supply, which is 0/00 meters away from radar station/KLOC-0. On the three-phase line, I-class classified test impulse current Iimp is selected, and the amplitude current of 50KA( 10/350μs) passes through SPD. SPD2 is installed on the switchboard of the radar station building, and SPD with nominal discharge current of 40KA(8/20μs) is selected for the three-phase line and neutral line. SPD3 is installed on the switchboard of the radar main room, and SPD with nominal discharge current of 10kA(8/20μs) is selected for the three-phase line and neutral line.

5. Grounding

The grounding treatment of meteorological radar station follows the grounding principle of "* * * ground is not * * *", that is, lightning protection grounding, power supply grounding, power supply protection grounding, anti-static grounding and logic grounding are combined into a qualified public * * * grounding network. In addition to the natural grounding of buildings, about 5000 artificial auxiliary grounding bodies are added to the grounding of meteorological radar stations, and the grounding resistance of the public grounding network formed is 0.8 Ω, which meets the requirements of meteorological radar stations for grounding resistance under the condition of soil resistivity.

Third, the application of comprehensive lightning protection technology in telecommunication system

Not only the lightning protection and grounding of buildings, but also the lightning protection and grounding of electrical systems and electronic equipment should be considered.

(1) CATV system

The lightning protection and grounding of CATV system should include front end, trunk line (including super trunk line) and power distribution system.

1. front lightning protection grounding?

The front-end computer room is generally not an independent building. Therefore, the whole building lightning protection grounding system can protect the safety of the front-end computer room system equipment, and there is no need to do lightning protection grounding, but there are several points to be noted: lightning may access the front-end system from the receiving antenna; The ground of the broadcasting room is anti-static floor, and the signal cables and power cables are buried in trenches. When the open wire of power line is introduced, lightning may string in from the power grid.

2. Lightning protection and grounding of trunk lines

The trunk line (including super trunk line) of CATV system includes electric (optical) cable and trunk equipment (such as amplifier or optical receiver). When the component is placed outdoors, lightning protection must be considered. ?

2. 1 lightning protection and grounding of electric (optical) cables?

For electric (optical) cables laid underground, the metal pipe or cable metal sheath shall be connected with lightning protection grounding device at the down lead and down lead; Both ends of the hanging wire of urban overhead electric (optical) cable and the metal pipeline in the overhead electric (optical) cable line shall be grounded; For outdoor overhead electric (optical) cable lines in suburbs, lightning rods shall be installed at every 10 ~ 15 pole of branch pole, lead pole, terminal pole, angle pole with angle depth greater than 1m, and straight pole. The messenger wire shall be grounded, and the grounding device shall be 35mm×35mm×2000mm angle steel or 65,438+.

2.2 Lightning protection and grounding of trunk equipment?

The housings of optical receiver, trunk amplifier and power supply shall be grounded nearby, but shall not be connected with the grounding wire of power transformer and cable broadcasting; For amplifiers and power supplies that need external power supply, power arresters should be installed according to the requirements of lightning protection standards. ?

(2) Computer room system

1. Equipotential bonding grounding system and * * *

For the lightning protection facilities of computer room system, the key of equipotential connection is to arrange an equipotential connection network with star structure (S-type) or mesh structure (M-type) or a combination of S-type and M-type in the computer room of information system, so that the metal shell, cabinet, rack, outer layer of shielding wire and grounding terminal of various surge protectors (SPD) in the computer room can be connected to the equipotential connection network in the shortest distance. In order to optimize the design of grounding type, some grounding materials with good conductivity, strong thermal stability, corrosion resistance and strong lightning current resistance should be selected, such as high-efficiency anti-corrosion resistance reducer, copper, cast steel grounding electrode and ion grounding electrode.

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The attenuation calculation of lightning electromagnetic field intensity can provide guidance for the arrangement of information system equipment and corresponding shielding measures. According to the calculation results, the main computer room of information system should generally be located in the center of the low-rise building, and the information system equipment should be as far away from the structural column of the external wall of the building as possible, and set in the area with the highest lightning protection level.

3. Selection and application of surge protector

3. 1 Selection and configuration of surge protector for low-voltage distribution system

Energy cooperation includes cooperation with or without decoupling elements, cooperation with trigger SPD, cooperation between two voltage switching SPDs, cooperation between voltage switching SPD and voltage limiting SPD, cooperation between two voltage limiting SPDs, and cooperation between the last SPD and the protected equipment. Despite the correct energy coordination, if SPD is not installed on or near the lightning protection zone interface and the protected equipment, the terminal of the equipment may still be damaged. The reason is that the line between SPD and the protected equipment may cause oscillation, which will lead to high voltage more than twice the SPD residual voltage and damage the equipment.

3.2 Selection and Configuration of Signal Line Surge Protector

According to the working voltage, interface type, characteristic impedance, insertion loss, power, signal transmission rate, frequency band width, transmission medium parameters, etc. of the protected equipment, the signal line SPD should be selected with small insertion loss and limited voltage not exceeding the withstand voltage of the equipment port.

3.3 Selection and Configuration of Feeder Surge Protector

The maximum transmission power of SPD selected on the antenna feeder should be 1.5-2.0 times of the average power. Other parameters, such as operating frequency, standing wave, insertion loss, characteristic impedance and interface, should meet the requirements of the system.

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