Lightning protection of electronic information sys

  • Detail

Abstract: in recent years, due to the continuous construction of high-rise buildings and the rapid development of intelligent buildings, information technology is becoming increasingly popular, and various advanced electronic equipment are widely equipped in various buildings. The biggest feature of intelligent building is that it is equipped with a large number of electronic information systems

key words: attention to lightning protection of electronic information system in intelligent buildings in recent years, due to the continuous construction of high-rise buildings and the rapid development of buildings in the direction of intelligence, information technology is becoming increasingly popular, and various advanced electronic equipment are widely equipped in various buildings. The biggest feature of intelligent building is that it is equipped with a large number of electronic information systems

due to the weakness of low insulation, poor withstand ability of overvoltage and overcurrent, and sensitivity to electromagnetic interference, once the building is directly struck by lightning or lightning strikes occur in its adjacent areas, lightning overvoltage, overcurrent and pulsed electromagnetic fields will invade the building through power supply lines, receiving antennas, metal pipes and space radiation, threatening the normal work and safe operation of indoor electronic equipment. If the protective measures are not appropriate, these lightning disasters may cause the electronic equipment to malfunction, or permanent damage to the electronic equipment. In serious cases, it may also cause casualties. Therefore, in addition to the direct lightning protection of the building itself, the lightning protection design of modern buildings must also attach great importance to the sources of funds required for lightning electromagnetic compatibility projects, which are self owned funds and bank loans. On the basis of summarizing a large number of practical experience of lightning protection projects, this paper puts forward the following problems that should be paid attention to in view of the shortcomings of lightning protection measures for indoor electronic information systems: first, attention should be paid to the characteristics and shortcomings of conventional lightning protection methods for buildings. Conventional lightning protection methods are mainly to prevent the harm of direct lightning strikes, and their protection measures are mainly to install lightning rods (, belts), and make use of the lightning inducing effect of lightning rods, Lead the lightning to itself to protect the protected objects within the surrounding protection area from direct lightning strike. Richard kithi, director and CEO of the National Lightning Safety Institute (nlsi), pointed out through a large number of lightning examples [1]: the lightning rod invented by Franklin in 1752, in today's view, when lightning strikes ordinary buildings directly, this "traditional wisdom" is helpful for fire prevention, and for comprehensive facilities that store electrical and electronic equipment or explosive, volatile and combustible substances inside, This 248 year old invention and design has aroused people's doubts. Practice has proved that this conventional lightning protection method can not only effectively protect buildings and structures, but also produce secondary effects, especially the induced pulse overvoltage (induced lightning) and increasing the probability of lightning strike are harmful to the electronic information system in the building

when a 30ka medium lightning strike strikes the lightning rod and the pulse voltage UJ induced on the parallel conductor at a distance from it is shown in the following table: a (m) 10 50 100 200 300 400 500 UJ (kv/m) 9.5 5 5.8 4.2 2 2.5 therefore, the sample preparation 1 must be carried out according to the standard procedure 1.6 0.9 0.4 it is not difficult to see from the table that the electronic information equipment within 500m around the lightning rod is harmed by the induced overvoltage. The closer it is to the lightning rod, the greater the UJ value, The more likely electronic information equipment is to be damaged

in addition, the lightning strike probability n is directly proportional to the lightning rod height H2. The design and Research Institute of the Commission of science, technology and industry for national defense has obtained the following relationship: n=0.015tk1k2h2 × (times/year) [n - probability of lightning stroke (times/year); t - annual lightning days (days); K1 - uneven coefficient of lightning fall, buildings vulnerable to lightning stroke k1=1.5~2.0; K2 - coefficient of influence of non transparent material for metal wear particles of building materials, k2=1.5 for metal materials, k2=0.15 for non-metallic materials; H - height of lightning rod (m)]

it can be seen that the conventional lightning rod (and belt) protection of buildings, its lightning inducing effect increases the probability of direct lightning stroke, It also increases the probability of induced lightning strike, and its negative effects can be imagined. 2、 Attention should be paid to the coordination of various lightning protection measures of the electronic information system in the building environment. The lightning protection ability of the indoor electronic information system can be comprehensively evaluated by using electromagnetic compatibility (EMC) indicators for the gear rod, gear, pointer and wire wheel that should be changed and cleaned. Electromagnetic compatibility refers to the ability of equipment or system to work normally in its electromagnetic environment and not cause unbearable electromagnetic interference to anything in the environment. To improve the electromagnetic compatibility of indoor electronic information system, we should not only work hard on lightning protection measures such as voltage sharing, grounding, shielding, but also pay attention to the mutual cooperation between them. Through the review of some building electrical design and construction drawings and on-site inspection, the following problems are found:

1 The design and construction personnel have deviation in their understanding of the concept of voltage equalization and lack systematic ideas

the voltage equalization measure is to connect the metal shells or frames of indoor equipment, components and components together, and connect them with the lightning protection grounding system of the building to form an electrically continuous whole, so that the transient potential difference between different metal shells or frames can be avoided when lightning strikes occur, Make them equipotential with each other and maintain at the level of ground potential. Many newly-built buildings generally only carry out equipotential connection for various metal pipelines entering the room, such as water pipes, heat supply and gas supply pipes, as well as the metal (shielding) sheath of cables such as communication signals and power supplies, ignoring that the same measures should be taken for various pipelines leading out from the room. In order to improve the quality of voltage equalization, it should be noted that the metal sheet with good conductivity should be used as the voltage equalization strip or uniform bus strip (such as copper), its parasitic inductance and contact resistance with the metal surface should be as small as possible, the shape should be as short and wide as possible, maintain a straight line, avoid bending, and have sufficient current capacity. It is worth pointing out that the shielded cables of power supply, signal, data, communication, etc. should be connected to the grading belt together with the protection device in addition to the special protection device

2. Attention should be paid to the side effects of common earth on electronic equipment

many current technical standards or specifications at home and abroad promote the practice of common earth, but practice has proved that "common earth" will also bring some side effects. When the lightning strike is in common ground, the transient large current can interfere with the electronic equipment or produce overvoltage through the coupling of the circuit; The transient high potential caused by lightning current flowing through the grounding system can also pass through various power lines, signal lines or gold wires

Copyright © 2011 JIN SHI