With the rapid development of information technology, intelligent building construction to the development of automation, information technology and energy-saving direction, microelectronic applications for the new technology represents technology has penetrated into all application areas of intelligent building and growing . There are many and complex microelectronic devices in buildings. These microelectronic devices are usually weak current devices with low overvoltage resistance and high interference prevention requirements, and they are most afraid of lightning strikes. When a lightning strike occurs, part of the energy (about 50%) leaks into the ground through the lightning protection device outside the building, and the other part of the energy is induced or coupled to the metal pipeline through the lightning current and enters the building to destroy the equipment. Therefore, the lightning protection of the intelligent building Protection is becoming more and more important.
Second, the main technical measures integrated lightning protection of intelligent buildings
first line of defense is to intercept direct lightning lightning information. The most economical and effective method is still the lightning rod (lightning strip, lightning net) method. Although lightning protection has many negative effects on electronic information equipment, it should adopt a positive and prudent attitude toward advantages and avoid disadvantages, and adopt effective technical measures to restrain them.
mask is one of the fundamental means of preventing any form of electromagnetic interference. The purpose of shielding is to limit the spread of electromagnetic energy inside a certain area, and to prevent or reduce the spread of external electromagnetic radiation energy to the protected space. Due to the different properties of electric field, magnetic field and electromagnetic field, the shielding mechanism is also different. According to the different shielding requirements, the complete shielding body of the shielding room (box, tube) or the incomplete shielding body of metal mesh, wave guide and honeycomb structure can be used respectively. Shielding is generally divided into electric field shielding, magnetic field shielding and electromagnetic field shielding.
①Electrostatic shielding (electric field shielding)-in order to eliminate and suppress the interference of electrostatic electric field.
②Magnetic field shielding-in order to eliminate or suppress interference caused by magnetic field coupling. Magnetic field shielding is divided into low-frequency shielding and high-frequency magnetic shielding.
③Electromagnetic field shielding-in general, a pure electric or magnetic field is rare in a space far from the interference source. The interference occurs in the form of high-frequency electromagnetic field radiation that exists at the same time as the electric field and the magnetic field. The lightning electromagnetic pulse can be regarded as a plane electromagnetic field propagation under far-field conditions. Therefore, the shielding of electric and magnetic fields should be considered at the same time.
④ Full shielding of signal transmission cables-cable shielding is a very important technical measure. It requires that all overhead and buried cables inside and outside the machine room be shielded with a metal layer to prevent interference from lightning electromagnetic pulses , This is called full shielding. When the fully shielded cable touches or passes through another metal part, the intermediate point should also be used. Therefore, fully shielded cables require multiple grounding.
3 equipotential connecting
equipotential bonding conductor is to make all interconnected good conductivity, and a ground communication system. Among them, the non-live conductors are directly connected by wires, and the live conductors are connected by lightning arresters. Its essence is to form a potential compensation system by a reliable grounding system, metal wires for equipotential connection, equipotential connectors (that is, lightning arresters, grounding isolators) and all conductors. The function of this potential compensation system is to provide a low-impedance continuous channel for the lightning current, so that it can be quickly introduced into the earth to discharge. The second is to prevent the various parts of the system from generating enough potential differences to cause damage. That is, in the very short time that the transient phenomenon exists, this potential compensation system can quickly establish five equipotential regions between all conductive parts in the area where the protected system is located. This area may have a potential difference of tens of kilovolts relative to the outside world. The important thing is that in the area where the system needs to be protected, there can be no significant potential difference between all conductive parts, so as to achieve the purpose of protecting equipment and personal safety.
The objects that need equipotential connection mainly include: a. Uncharged metal objects. Such as various metal pipes, cable shielding layers, metal bases and metal shells of equipment. b. Charged metal objects. Such as power cords, various signal transmission lines, etc.
The process of discharging lightning current energy to the ground should conform to the principle of hierarchy. Hierarchy is to classify and release lightning energy according to the divided lightning protection zones. As much and as quickly as possible, vent the excess energy into the ground before introducing it into the information system. Because the energy of lightning overvoltage is very large, a single measure or a line of defense cannot eliminate the damage of lightning overvoltage. Multi-level protection measures must be taken to limit the intrusive lightning overvoltage within a safe range that the equipment can withstand.
One of the most effective means of grounding is split and bleed direct lightning and lightning electromagnetic interference energy, but also the basis for potential equalization compensation system. The purpose is to discharge the lightning current to the earth through the low impedance grounding system, thereby protecting the safety of buildings, personnel and equipment. Without a good grounding system or poorly grounded lightning protection facilities will become a disaster for lightning into the room; poor grounding of lightning protection devices also provides opportunities for lightning electromagnetic pulses to produce inductive and capacitive coupling interference to electrical and electronic equipment.
Third, a comprehensive lightning protection design Intelligent Building
1 lightning protection
for direct lightning strike protection, diversion measures can be taken, the use of lightning rods, lightning belt, lightning network lightning current into the earth along the deflectors to prevent direct lightning strike In buildings or equipment.
Air-termination tapes, air-termination nets or air-termination rods should be used as air-termination devices on the roof of buildings. The air-termination net (belt) should be laid along the corners, ridges, eaves and corners of the roof and other parts that are vulnerable to lightning strikes, and an air-termination grid that should not be larger than 10m×10m or 12m×8m should be formed on the entire roof. The steel bars in the building’s reinforced concrete roof, beams, columns, and foundations are used as down conductors to make the entire building a frame cage structure. The lightning net (belt) should be Φ12 galvanized round steel or -40×4mm galvanized flat steel. There should be no less than two dedicated down conductors, and they should be arranged evenly or symmetrically along the building’s circumference, and their average spacing should not be greater than 18m.
2 Lightning protection of power supply system
Because lightning produces strong over-voltage and over-current, it is impossible to complete current discharge and voltage limitation at one time, so the power system must adopt multi-level lightning protection, at least two levels of lightning protection before and after current discharge and voltage limitation must be adopted. . According to the current relevant regulations and requirements in my country, the power system should adopt multi-level lightning protection. That is, install a first-level lightning protection device where the power line enters the LPZ1 area from the LPZ0B area, and install a second-level lightning protection device where the power line enters the LPZ2 area from the LPZ1 area, and the equipment power supply and UPS power input that need to be protected Install a third-level lightning protection device at the end, and set up precision protection for the power supply. Through the use of multi-level power supply lightning protection measures, the lightning overcurrent is completely discharged and the overvoltage is restricted, so as to prevent as much as possible the lightning from entering the electronic information system through the power line and damaging the system equipment.
① PB25-385/B+C/4 (limp=25kA, ln=25KA, Up=1.8KV, Uc=385V) can be used at the main power distribution cabinet where the power line enters from the LPZ0B zone into the LPZ1 zone. Phase surge protector, the test category is Type I test. The front end is connected in series with a 63A power circuit breaker as the first-level lightning protection of the power system.
②PC40-385/4 (ln=20KA, Up=1.7KV, Uc=385V) power supply three-phase surge protector can be used at the power distribution cabinet. The test category is Type Ⅱ test, and the front end is connected in series with 32A power supply disconnection As the second-level lightning protection of the power supply system.
③ PD20-275/4 (ln=10KA, Up=1.2KV, Uc=275V) power three-phase surge protector can be used at the power distribution box of the equipment and the UPS power inlet end that needs to be protected. The test category is Class II test. The front end is connected in series with a 32A power circuit breaker as the third-level lightning protection of the power system.
④PC40-85VDC (ln=20KA, Up=0.5KV, Uc=85VDC) DC power surge protector can be used at the DC screen. The test category is Type II test, as the lightning protection of the DC power system.
⑤ PDU1-J1G08/16 (ln=5KA, Up=1.2KV, Uc=275V) type power distribution unit surge protector can be used at the power supply of the equipment in the computer room. The test category is Type II test as the end lightning protection of the power system. protection.
Lightning 3 signal lines of
information within the network is no longer a modern building islands of information, it must be an open network interconnection, to meet the needs of people exchange information. The connection of physical media is required between buildings and between buildings and external networks. There are many ways of communication between the internal network and the external network. Some are interconnected by ordinary telephone twisted pair as the communication medium, such as PSTN. (Dial-up access), ISDN technology, DDN technology, ADSL technology, etc.; some use Category 5 unshielded twisted pair, optical fiber as the medium to achieve communication connection.
In the above-mentioned communication methods, in addition to the optical fiber medium (the metal inside the optical fiber should also be equipotentially connected at the entrance), other mediums may be subjected to direct lightning or induced lightning to infringe the network system connected at both ends.
In order to avoid the possibility of lightning damage caused by communication cables, the usual technology is to connect the signal lightning arrester (signal SPD) before the cable is connected to the network communication equipment, that is, a transient overvoltage protector is connected in series in the link. It can protect electronic equipment from conducting surge overvoltage caused by lightning strikes and other interference, block the intrusion of overvoltage and lightning waves, and reduce the impact of lightning on system equipment as much as possible. Since the signal arrester is connected in series in the communication line, the signal arrester must meet the requirements of network performance indicators such as signal transmission bandwidth in addition to the lightning protection performance characteristics. Therefore, when selecting related products, full consideration should be given to lightning protection performance indicators and network performance indicators such as network bandwidth, transmission loss, and interface type.
SNH-RJ45/16 (ln=3KA, Up≤25V, Uc=6V) network signal surge protector can be used for signal line lightning protection, and the test category is Type II test. As the lightning protection on the network signal system.
Lightning protection of 4 antenna feeder system
The antenna feeder system is one of the important components of microwave relay communication. The antenna converts the electromagnetic wave transmitted in the feeder into the electromagnetic wave transmitted in the free space, or converts the electromagnetic wave transmitted in the free space into the electromagnetic wave transmitted in the feeder. The feeder is the transmission channel of electromagnetic waves. When a coaxial cable is used for the feeder, a coaxial SPD with a nominal discharge current of not less than 5KA should be installed at the entrance of the coaxial cable into the computer room. The grounding lead of the coaxial SPD grounding terminal should be from the grounding wire and flashing on the outside of the antenna feeder entrance. Belt or ground net lead connection.
The lightning protector of the antenna feeder can adopt PR-F, PR-N and other antenna feeder lightning protectors according to the interface form, the nominal discharge current ln=10KA, the voltage protection level Up≤600V, the insertion loss≤3dB, the standing wave ratio≤ 1.2, as the lightning protection on the antenna feeder line.
5 Lightning Monitoring System
monitoring system front-end equipment outdoor and indoor two types of equipment installed in the room are generally not subject to direct lightning, is mounted on the outside of the device, most in a relatively open area, a greater risk of direct lightning, it must be Consider the problem of direct lightning protection. The front-end equipment of the security monitoring system, such as cameras, should be placed within the effective protection range of air-termination devices (air-termination rods or other air-termination conductors). For front-end equipment that is already within the protection range of other air-termination systems or high-rise buildings, it is generally no longer necessary to consider direct lightning protection; for front-end equipment that is not within the protection range of any air-termination system, both The problem of direct lightning protection should be considered. From a technical and economic point of view, it is not feasible to install an independent air-termination rod for direct lightning protection of front-end equipment. Generally, the air-termination rod is erected on the support rod of the camera. The downline can directly use the metal rod itself (also can use Φ8 galvanized round steel or 30×3mm galvanized flat steel), but in order to prevent electromagnetic induction, the power line and signal line of the camera along the pole should be laid through a metal pipe, and the metal pipe should be reliably grounded.
Statistics show that more than 80% of lightning accidents in the security monitoring system are caused by the overvoltage of lightning intrusive waves induced on the lines connected to the system. Therefore, protecting the lines connected to the system is a link that cannot be ignored in the overall lightning protection. Effectively connect the metal sheath and metal tube of the cable to the lightning protection ground at the entrance end. Corresponding lightning protection devices should be installed at both ends of all transmission lines.
Install SV-BNC (ln=3KA, Up≤40V, Uc=12V) video signal lightning protection device at the front end of the monitoring host, and the test category is Type II test. As the lightning protection on the transmission line of the monitoring system;
install OP-SV3/24 three-in-one surge protector in front of the camera, the power part parameters are (ln=5KA, Up≤900V, Uc=275V), and the control signal part parameters are ( ln=3KA, Up≤40V, Uc=12V), the test category is Type II test, used as lightning protection for the camera’s power supply line, signal line and control line.
6 equipotential bonding
all water entering the building or other metal pipes effectively grounded upon entering the building and with each reservation equipotential connector in electrical communication. The connection uses 16mm2 stranded copper wire. All metal components and non-charged metal enclosures in the building must be connected to each other with 6mm2 copper wires and be reliably connected to the grounding busbar. According to the requirements of GB50057-2010, the functional equipotential connection between various boxes, shells, racks and other metal components of an electronic system and the building grounding system should be S-shaped star structure or M-shaped. The mesh structure is connected, so 40mm×4mm copper bars are used in the machine room to be laid along the periphery of the machine room, and the main steel bars of the eight structural columns of the outer building of the machine room are electrically connected to the grounding busbar one by one. All the metal parts in the machine room are connected to the grounding busbars one by one.
all of the metal wires in the building, including power cables, communication cables and signal cables are made through shielded wire and metal tube shield, on the room walls, metal doors and windows to be effective welding and reserve ground member , So that the entire computer room forms a Faraday cage to prevent external electromagnetic pulses from interfering with the equipment in the computer room.
8 Reasonable wiring design
Anti-lightning electromagnetic pulses have very strict requirements on indoor wiring. Because the steel bars in the reinforced concrete column used for down conductors and the shielding net of the entire building are located at the outer wall, the lightning current needs to be shunted to the grounding device through the steel bar here, so the current density at the outer wall is high, and the electromagnetic field is strong. . The main lines of power and communication lines in the machine room should be set near the elevator shaft in the center, and various electrical feeders in the building are protected by metal pipes or double-shielded cables (or coaxial cables).
9 Ground system design
based on available basic information soil resistance and soil distribution, according to the principles of scientific and rational, economical, should be equalizing, equipotential principle, joint grounding system, lightning protection and grounding, low voltage distribution system (protection ) Grounding, working grounding, shielding grounding, equipotential grounding, etc. share the same grounding system. The building should use its reinforced concrete foundation as the ground network. Its power frequency grounding resistance should not be greater than 1 ohm. If the soil resistivity is high and the grounding resistance is difficult to meet the requirements, you can reduce the resistance by adding artificial grounding bodies and using resistance-reducing materials.
Set the total equipotential terminal at the entrance of the building and connect it with the grounding device. Connect the grounding of all metal pipes and cables that enter the building, such as the grounding of the antenna feeder, the grounding of the fiber optic cable reinforcement core, and the grounding of the shielded pipe of the power supply line.
The material selection of the grounding device, the metal grounding body should be made of hot-dip galvanized material. Since the original hot-dip galvanized layer has been destroyed at each welding point, anti-corrosion treatment must be done. The length of the vertical grounding body is 1.5-2.5m, and the interval of the vertical grounding body is 1.5-2 times of its own length. The upper end of the grounding body is not less than 0.7m from the ground, and it should be under the frozen soil layer. The vertical grounding body can be made of ∟50*50*5mm angle steel or grounding copper rods, and the horizontal grounding body and grounding lead-in can be made of -40*4mm flat steel and grounding modules, and materials such as resistance reducing agents can be added to reduce the grounding resistance.