Lightning protection measures for the hottest wire

Lightning protection measures for cable network equipment

every summer, due to more thunderstorms and abnormal climate, it is the peak season for cable TV system failures. Lightning is very harmful to cable TV system, so lightning protection, lightning protection and grounding have become urgent problems to be solved

lightning strikes are generally divided into three categories, namely direct lightning strikes, induction lightning that makes it an environment-friendly "green product" and lightning intrusion waves. The direct lightning strike rate is only about 10% of the lightning strike rate, and the harm range is generally small. Lightning rods, lightning wires and lightning protection can be used to protect. Although the induction lightning is not as strong as the direct lightning strike, its probability of occurrence is much higher than the direct lightning strike. Moreover, the induced lightning over-voltage can be transmitted far through the power line, antenna feeder, output cable, etc., expanding the scope of influence, The electronic equipment of the cable TV system was damaged by lightning strike according to the actual situation of each city, which was mainly caused by induction lightning. Induction lightning does not contain much energy, and there are certain rules to follow. It can be prevented by various correct and effective lightning protection measures. The electromagnetic induction of lightning current causes extremely high voltage on the metal conductor to discharge, which is called inductive lightning. Even if the electronic equipment of the cable TV system is within its protection range, it may still be damaged by lightning, most of which are fuses and power transformers. Rectifying elements, three terminal voltage regulators, and serious damage to integrated circuits and other components may also be caused by inductive lightning. Generally speaking, lightning intrusion is mainly through the following three ways:

1, intrusion by power lines. When the mains power supply equipment and lines are struck by lightning, the average Lightning Overvoltage on the 220/380 V power line can reach 10000 v. the lightning impulse wave invades the microelectronic equipment and system along the power line, which can cause a devastating blow to the system equipment

2. Invaded by various transmission networks. The invasion of communication and network lines can be divided into two cases: (1) when the ground protrusion is hit by direct lightning, the strong lightning voltage will puncture the adjacent soil, and then puncture the cable sheath of communication and network lines, so that the high voltage invades the network system; (2) When Leiyun discharges to the ground, it induces an overvoltage of thousands of volts on the communication and network lines, damaging the network system equipment connected to the lines

3. The ground potential counterattacks the invasion of voltage through the grounding body. When lightning strikes the lightning rod, a radial potential distribution will be generated near the grounding body of the lightning rod, which will generate a high-voltage ground potential counterattack against the grounding body of electronic equipment close to it, and the intrusion voltage can be as high as tens of thousands of volts

therefore, specific lightning protection measures should be formulated according to the above lightning intrusion characteristics. Among the current lightning protection measures, the most effective and widely used method is grounding, that is, the charge generated by lightning is completely or partially introduced into the ground to avoid lightning accidents

since cable TV transmission networks are all over urban and rural areas, optical cables and cable lines span various complex terrain, it is very important to do a good job in lightning protection to ensure the safe and high-quality broadcasting of cable TV

I. lightning protection measures at the front end

the front end is the core of the entire cable TV system, including various open-circuit antennas, satellite antennas, satellite receivers, modulators and demodulators, optical light-emitting receivers and other equipment. In case these devices are damaged by lightning, in addition to causing serious economic losses, it will also cause a wide range of suspension of broadcasting, which will affect the image of cable stations. Therefore, the lightning protection measures at the front end are very important. There are two main types of lightning protection at the front end. 1. Lightning protection of receiving antenna; 2. Lightning protection of power supply

1. Lightning protection measures for the receiving antenna include: A. determine the geographical location of the receiving antenna, and ensure the quality of the received signal and avoid the minefield when erecting the antenna; B. Add a signal lightning protector. The main function of this lightning protector is to make the signal pass smoothly. In case of abnormal high voltage caused by lightning, it will immediately act on its internal amplification tube to prevent lightning from damaging the equipment; C. Lightning rod is a common and effective lightning protection measure. Since the receiving antenna is usually erected on the roof, it is easy to introduce lightning into the front end, especially the satellite antenna. Lightning protection measures must be considered comprehensively. On the one hand, the receiving antenna should be in the protection area of the lightning rod, on the other hand, the grounding resistance of the lightning rod should be reduced. The lightning rod should be made of high-quality metal materials with a larger diameter, It should be buried underground and reliably grounded, and the grounding resistance should be controlled within 4 Ω

2. Lightning protection measures for power supply: A. install power lightning arrester. When the municipal power supply generates high pulse voltage due to lightning strike or other factors, it will damage the equipment on the circuit. Therefore, install power lightning arrester in cable TV room. Its function is to release a large amount of pulse energy generated by inductive lightning strike on the circuit to the safety ground wire in the shortest time, so as to protect the front-end equipment in the machine room; B. Do a good job of working grounding. In the cable TV system, the AC power used is generally provided by the low-voltage power supply with ungrounded neutral line. The electrical equipment using the AC power provided by this low-voltage power supply should take protective grounding measures, that is, implement working grounding. This protective grounding measure is to reliably connect the metal shell, frame and other electrical equipment with the earth with grounding devices, Working grounding ensures that the working ground potential in the machine room is zero potential. Working grounding can help them reduce the overall size of the product, and at the same time, it can drain the leakage of equipment and the static electricity generated by various friction. The lightning brought into the metal protective layer of signal input and output cables and optical cables in the machine room is also discharged through the working grounding, so the working grounding plays a role in protecting equipment and protecting the personal safety of workers