Research on lightning voltage protection measures

2022-10-01
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Research on lightning voltage protection measures of communication facilities

preface

with the rapid development of science and technology, large-scale integrated circuits and intelligence are widely used in communication equipment, making various advanced communication equipment have higher and higher requirements for overvoltage. Since the harm caused by the instantaneous overvoltage induced by lightning on the power line, signal line, antenna feeder, etc. often occurs, appropriate protective measures must be taken to avoid the harm to transmission lines, communication equipment and personnel caused by overvoltage and the resulting overcurrent.

lightning is a natural phenomenon, which has brought a lot of harm to human society. The International Electrotechnical Commission has called lightning disaster "a major public hazard in the electronic age". Lightning, induction lightning, power supply sharp wave and other instantaneous overvoltages have become the culprits of the destruction of electronic equipment. From the analysis of a large number of lightning stroke cases of communication equipment, experts believe that lightning electromagnetic pulse (LEMP) caused by lightning induction and lightning wave intrusion is the main reason for the damage of communication equipment. Therefore, only by understanding its formation process and seeking effective protective measures can we reduce the losses caused by lightning. According to meteorological observations, there are about 100 lightning strikes per second on the earth. According to the code for design of special telecommunication buildings, communication buildings are generally equipped with lightning rods, lightning rods or lightning strips, and all of them adopt the mode of joint grounding. Formally, it has a good performance of lightning protection and anti external electromagnetic interference. However, why do communication equipment sometimes suffer from overvoltage and overcurrent damage? Will it even pose a threat to the personnel of operation and maintenance personnel? This is because when lightning occurs, the charged clouds will rapidly expand in the field of new utilization of communication facilities and the production cost will decline, making the use of small metal new materials to generate induced charges on the increasingly basic and popular antenna, or lightning induction will invade through communication and power lines. If the DC path between the antenna and communication cable and the earth is not smooth, It will cause overvoltage due to the induction of high potential between the antenna and cable and the earth, so that the communication facilities cannot withstand the intrusion of strong current and will be damaged, and even endanger the personal safety of operators.

with the acceleration of the construction of Yangtze River communication and the large-scale application of advanced communication equipment in Yangtze River communication, a single protection system can no longer meet the requirements of modern communication network safety. Our bureau has also increased the investment in lightning protection and grounding system, and the protection system is becoming more and more perfect. The protection system has been changed from a single protection system to multi-level protection. Multi level protection includes protection against direct lightning strike, induced lightning, instantaneous overvoltage caused by ground potential counterattack and other aspects. The protection points and protection levels should be determined according to the different functions and different protected processes of all microelectronic equipment such as digital program control, digital microwave, VHF, photoelectric transmission, AC and DC power supply. According to the possible intrusion channels of the harm of instantaneous overvoltage caused by lightning, multi-level protection should be achieved from the power line to the data communication line. Therefore, the precautionary principle we should adopt is "overall defense, comprehensive treatment and multiple protection", and strive to reduce the harm it produces to the lowest point.

I. lightning protection measures for communication facilities

generally speaking, there are four ways to facilitate debugging and inspection and avoid lightning strikes on buildings and equipment: ① dredging, that is, the charge in the thunder cloud is dredged to the earth through the lead, so as to avoid direct lightning strikes or induced lightning current flowing through buildings or communication equipment, so as to protect buildings or communication equipment from lightning strikes. ② Isolation, that is, to isolate the overvoltage generated by lightning from the protected object, so as to avoid lightning strike. ③ Equipotential, that is, the iron tower ground, antenna feeder ground, equipment working ground, public ground of buildings, etc. are placed on equipotential. ④ Neutralization, that is, to release the opposite charge and the charge in the thunder cloud for neutralization, so as to prevent the formation of lightning. According to the above four lightning protection methods, specific to the lightning protection overvoltage of a communication project, the main measures are as follows.

1. external protection

external protection is mainly protected by lightning rods (lightning rods, lightning wires and lightning strips) and grounding devices (grounding wires, grounding electrodes). The protection principle is: when the thunder cloud discharges close to the ground, it distorts the electric field on the ground, and forms a partial electric field intensity distortion on the top of the lightning rod (lightning wire), so as to affect the development direction of lightning first introducing electricity, guide the lightning to discharge to the lightning rod (lightning wire), and then introduce the lightning current to the earth through the grounding downlead and grounding device, so as to protect the protected object from lightning, This is an effective method to prevent direct lightning strike, which has been proved by long-term practice. However, the passive discharge lightning rod has some shortcomings, such as poor reaction speed, small protection range and small conductivity. According to the requirements of modern communication development, the lightning rod should choose the active lightning protection device with early discharge, and should be considered from different angles such as 30 °, 45 ° and 60 ° to achieve the protection of various lightning strikes, increase the protection range and increase the conductivity. All exposed metal components (pipes) of the building shall be well connected with lightning protection (lightning wire or lightning strip).

(1) requirements for installing lightning rod or grounding device ① the lightning rod should be installed several meters higher than the tip of the antenna, and there should be a certain interval between the lightning rod and the antenna. It is a two-dimensional crystal composed of carbon atoms, so as to prevent the existence of lightning rod from damaging the radiation pattern of the antenna and affecting the communication effect. The general practice is that the lightning rod becomes the main pole of the antenna tower, but the communication Tianqian is installed outside the lightning rod about 1.5 wavelengths.

② the resistance of the DC path of the lightning ground wire is required to be low enough, generally 10-50 Ω. Due to the large lightning surge current, wide spectrum and short duration, it is required to have as little inductance as possible.  

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