Lightning protection technology of intelligent bui

2022-06-14
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Intelligent building lightning protection technology

when human society enters the electronic information age, a large number of electronic equipment such as communication and computer are installed in the resulting intelligent building and form an intelligent system, which is called intelligent building. Intelligent buildings mainly include communication network system, information network system, building equipment monitoring system, safety protection system, generic cabling system, automatic fire alarm and fire linkage system, etc. A large number of computers and microelectronic equipment are used in these systems to provide services to users through detectors, controllers, network equipment, cabinets and so on throughout the building. Due to the characteristics of low power, low working voltage, low insulation, poor overvoltage bearing capacity and weak anti-interference and anti surge ability of computer and microelectronic equipment in intelligent buildings, once disturbed by lightning, it will not only damage the expensive equipment in the system, but also paralyze the operation of the whole system and cause huge economic losses. Therefore, it is particularly important to be familiar with lightning and master the protection technology of building intelligent equipment and its system against lightning attack

I. types of lightning action

the forms of lightning attack intelligent system mainly include direct lightning stroke, lateral lightning stroke, lightning induction, lightning wave intrusion, in addition to lightning electromagnetic pulse, etc

1. Direct lightning strike: lightning strikes the building directly. When lightning flows through the building and leaks to the earth, it will produce electrical effect, thermal effect and mechanical effect

2. Lightning induction: when lightning discharges, there will be a strong electromagnetic field around the lightning current passing through, resulting in a high induced voltage on the conductor or metal components passing through the current and power devices, sometimes up to hundreds of thousands of volts, which can completely damage the insulation layer of general electrical equipment; In the circuit of cross connection of metal components, sparks will be generated due to poor contact or contacts with gaps

3. Lightning wave intrusion: the effect of lightning on overhead lines or metal pipelines. Lightning will invade the interior of buildings along these pipelines, endangering the safety of intelligent systems and equipment

4. Lightning electromagnetic pulse (LEMP): the effect caused by direct lightning strike and nearby lightning strike as interference source. Most of them are interference through connecting conductors, such as lightning current or part of lightning current, potential rise hit by lightning and magnetic radiation interference

II. The proportion of various raw materials and the new characteristics of lightning disaster

when high technology is widely used, the characteristics of lightning disaster are very different from the past, and new characteristics appear. For example: (1) the affected area has increased, extending from the two industries of construction and electric power to other industries, especially the fields with wide application of high technology. Such as posts and telecommunications, computers, aerospace, intelligent systems, etc. (2) The spatial scope of lightning disaster has expanded from two-dimensional space intrusion to three-dimensional space intrusion. Lightning is a kind of pulsed electromagnetic field with large market use, direct strike and overvoltage wave transmitted along the pipeline and added to space lightning, which invades into any corner in the form of three-dimensional space and causes disasters everywhere. (3) The degree of lightning damage has been greatly enhanced, and the direct and indirect economic losses of lightning disasters have increased significantly. (4) The object of lightning disaster has focused on the expensive equipment using electronic devices or microcomputer. There is no doubt that intelligent buildings will be the main object of lightning damage

therefore, we must clearly realize that the importance, urgency and complexity of lightning protection engineering have increased to a considerable extent, and the lightning protection has changed from single protection to system protection. We must be familiar with and study the contemporary lightning protection technology according to the new characteristics and stand at a new height, so as to improve people's comprehensive ability to prevent lightning disasters

III. principle of lightning protection

due to the emergence and wide adoption of intelligent buildings and the new characteristics of lightning disaster, we must set up defense layer by layer in an all-round way, not only to discharge and intercept, but also to balance potential, shielding and isolation, overvoltage and overcurrent protection, so as to achieve the purpose of comprehensive lightning protection

IV. lightning protection measures

intelligent buildings are widely used in class I and II buildings. The lightning protection grade is usually class I and II. The impulse grounding resistance of class I lightning protection shall be less than 10 ohms, the impulse grounding resistance of class II lightning protection shall not be more than 20 ohms, and the grounding resistance of public grounding system shall be less than or equal to 1 ohm. In the project, the roof lightning strip, lightning arrester, lightning rod or mixed lightning arrester are used as the lightning receiving device, the reinforcement in the structural column of the building is used as the downlead, the foundation beam reinforcement, bearing platform reinforcement or pile foundation main reinforcement of the building are used as the grounding device, and they are well welded with the grounding wire. At the same time, the roof metal pipes, metal components, metal equipment shells, etc. are connected with the lightning receiving device, and the metal components or steel frames of the outer wall of the building and the outer ring beams of the building are connected with the downlead, so as to form a closed and reliable "Faraday cage". In the building, the equipment shell, metal distribution frame, wiring bridge, threading metal pipeline, etc. in the intelligent system are combined with the total equipotential or local equipotential. While the lightning arrester is installed in the high-voltage cabinet and low-voltage cabinet in the distribution system, the surge protector (SPD) is installed in the power box and signal line box of the intelligent system. So as to achieve the purpose of comprehensive defense against lightning and ensure the safety of intelligent buildings

(I) external lightning protection

the main devices for external lightning protection include lightning arrester, lightning downlead, grounding device, etc., which are mainly used to prevent direct lightning

1. Lightning arrester

(1) lightning rod: generally made of galvanized round steel or welded steel pipe. In the project, connect the lightning rod with the lightning down lead, or with the lightning strip, or with the lightning

(2) install 12mu diameter galvanized round steel as lightning strip at the corner, ridge, parapet and cornice around the roof vulnerable to lightning strike. 40mmx4mm galvanized flat steel shall be used on the roof, and a grid of no more than 10mx10m or 15mx15m shall be set, which is connected with the lightning strip

(3) structures on the roof or other objects protruding from the roof, such as brick water tank, stair top cover, elevator machine room top cover, roof shape, etc., shall be equipped with lightning protection belt along its four circumference; Galvanized round steel lightning strip with a diameter of 12mm shall be installed on the roof lightning arrester and buildings outside the protection scope, such as the roof of the podium of the main building and the channel connecting the single building; Metal objects on the roof of the main building, such as antenna, cooling tower, fire pipe or other water supply pipe, fan, stainless steel water tank, etc., must be connected with the roof lightning strip, and the section of the connecting line shall not be less than that of the roof lightning strip

(4) when the height of the building exceeds 30m, the balcony metal railings of 30m and above of the building, metal components such as metal doors and windows, steel frames or other metal projections on the outer wall must be connected with the lightning down lead to form an electrical path, so as to prevent lateral lightning stroke

2. Lightning down lead

lightning down lead usually uses the main reinforcement in the building structural column. When the diameter of the main reinforcement is greater than or equal to 16mm, two of the reinforcement shall be welded as a group of lightning down lead; When the diameter of the main reinforcement is less than 16 -, four of them shall be welded as a group of lightning down lead. The upper part of the lightning down lead is connected with the lightning strip, and the lower part is connected with the grounding device

3. Grounding device

at present, most buildings are buried deeper than 60.. The foundation reinforcement is used as the grounding device, and the two main reinforcements of the ground ring beam are used to form a closed ring. If the two main reinforcements of the ground beam ring are connected with the reinforcement at the bottom of the bearing platform. If there is a pile foundation, the main reinforcement of the pile foundation shall be connected with the main reinforcement of the ground beam ring as the grounding wire at the setting of the down lead

(II) internal lightning defense

internal lightning defense mainly includes defense against lightning induction, lightning wave intrusion and lightning electromagnetic pulse. The usual measures are shielding isolation, equipotential connection and grounding, installation of surge protector, etc

1. Measures to prevent lightning induction

(1) local equipotential box (LEB) shall be set in the central control room of intelligent system, computer network center, monitoring center, fire control room, machine room and equipment rooms on other floors. The terminal board in the local equipotential box shall be connected with the grounding body or the terminal board in the general equipotential box of the building by galvanized flat steel or copper plate or copper wire, and the metal equipment shell, cable bridge, threading metal pipe The equipment support, electrostatic floor support or other metal components shall be reliably connected with the terminal board in the local equipotential box

(2) install a galvanized flat steel or copper plate in the weak current shaft, connect the cable tray and the threading steel pipe of vertical pipeline with it every three layers, and connect the distribution frame, equipment cabinet or support in the shaft of each floor with the galvanized flat steel or copper plate

(3) the metal shells of various equipment installed on site in the building by the intelligent system, such as sensors, controllers, card readers, camera frames, etc., shall be connected to the local equipotential of the floor nearby

(4) the electrical path of cable tray, threading steel pipe and the connection between box and cabinet shall be good

2. Measures to prevent lightning wave intrusion

(1) power cables into buildings, especially cables for intelligent systems, shall be buried as far as possible. Install the general equipotential box on the bottom floor of the building, and connect the indoor fire pipes, various metal protective sleeves, cable metal protective layer, etc. with the terminal board of the general equipotential box with copper wire. If the intelligent system machine room is located on the ground floor, the metal pipe and cable metal protective layer can also be connected with the local equipotential terminal board in the machine room with copper wire. The interruption of metal pipe shall be bridged

(2) if overhead laying is required, the cable shall be replaced into the house, the lightning arrester shall be installed at the connection between overhead and cable, and the lightning arrester, cable metal sheath, protective steel pipe and other metal parts shall be grounded together

3. Measures to prevent lightning electromagnetic pulse

the protection of lightning electromagnetic pulse is to discharge lightning overvoltage and overcurrent to the ground by using shielding isolation, voltage sharing, overvoltage protection, overcurrent protection, grounding and other methods on all channels of lightning intrusion into the building (such as power lines, signal transmission lines and various pipelines entering the building), so as to achieve the purpose of protecting intelligent building equipment

4. Surge protector (SPD) protection in other areas

surge protector is a non-linear voltage limiting element, which is used to limit transient overvoltage and shunt surge current. It is divided into off type, voltage limiting type and hybrid type; According to the function of surge protector in intelligent system, it can be divided into power line surge protector, antenna feeder line surge protector and signal line surge protector

(1) the surge protection of power lines can generally adopt four levels. The third level surge protection box is installed in the main power distribution box of the machine room, in which the third level surge protection box is used for all equipment; The fourth level is installed in the power box of equipment requiring special protection (such as digital program-controlled switch, main switch of computer network system, etc.). Surge protectors at all levels of the power line shall be installed at the front end of the power supply of the protected equipment, and their terminals shall be connected with the corresponding phase lines of the power box; The grounding terminal is connected with the PE terminal board in the power box. The length of connecting wires of surge protectors at all levels shall not be greater than 0.5m

(2) the surge protector of antenna feeder line is connected in series between the antenna feeder and the protected equipment

(3) the signal line surge protector is installed on the signal port of the protected equipment, and its output end is connected with the port of the protected equipment

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