Summer is the peak season for cable television systems to fail. Lightning damage to the cable television system is very strong, so lightning protection, lightning protection and grounding issues have become an important topic for cable TV maintenance personnel.
As the cable television transmission network is spread over urban and rural areas, and optical cables and cable lines span various complex terrains, it is crucial to ensure the safety and quality of cable television broadcasting. In the initial stage of building the network, it is necessary to conduct investigations and investigations, survey routings, select grounding points for grounding lines, measure the soil resistivity of the ground trenches, review the meteorological data of the past years, and understand the distribution of lightning strikes. After grasping the relevant information, the following grounding methods can be used to prevent lightning strikes.
Front-end lightning protection measures
The front end is the core of the entire cable television system. The front end includes various open-circuit antennas, satellite antennas, satellite receivers, modulator demodulators, and light-emitting devices. In the event that these devices are damaged by lightning strikes, in addition to causing serious economic losses, they will also cause a wide range of outages. Therefore, front-end lightning protection measures are very important.
There are two main types of lightning protection at the front end:
1. Lightning protection of the receiving antenna. Lightning protection measures include: A. Determining the geographical position of the receiving antenna. When installing the antenna, it is necessary to ensure the quality of the received signal and avoid the minefield. B. Add the signal lightning protector. The main function of this lightning protection device is to make The signal passes smoothly, and in the event of an abnormally high voltage caused by thunder and lightning, its internal amplification tube immediately acts to prevent the lightning from damaging the equipment; C. erecting the lightning rod, which is a universal and more effective lightning protection measure. Lightning rods should be made of high-quality metal materials with relatively large diameters. They must be buried underground and reliably grounded. The grounding resistance should be controlled within 4Ω.
2. Lightning protection of the power supply. Lightning protection measures include:
The installation of lightning protection devices will damage the equipment on the circuit when the mains generates high pulse voltage due to lightning or other factors. Therefore, install a lightning protection device in the cable television room. Its role is to release a large amount of pulse energy generated by an induced lightning strike on the safety ground in the shortest time, so as to protect the front-end equipment in the computer room.
To do work grounding, in the cable television system, the AC power used is generally provided by a low-voltage power supply network that is not grounded on the neutral line. Electrical and electronic equipment provided by this low-voltage power supply network should adopt protective grounding measures. , that is, the implementation of the work grounding, this protective grounding is the electrical equipment, metal shell, frame and other grounding device and the earth reliably connected, the working ground to ensure that the working room ground potential is zero potential, through the work ground, you can escape Leakage of equipment can also discharge static electricity generated by various friction. Lightning carried by the signal input and output cables in the equipment room and the metal protective layer of the cable is also discharged through the working ground.
Light node lightning protection
The lightning protection of the optical node is also very important. The lightning protection measures of the optical node are mainly grounding and lightning protection of the power supply. In general, the optical receiver itself has a lightning protection device, but it needs a good grounding to really work. The optical node chassis is connected with the grounding body, and the optical receiver and the power supply box are connected with the optical node chassis, and all the device housings are guaranteed. All of them are reliably grounded. The lightning protection of the power node of the optical node must be equipped with a lightning protection device to release a large amount of pulse energy generated by the utility lightning due to the induced lightning strike on the grounding body, so as to protect the electrical equipment within the optical node and achieve better performance. The lightning protection effect.
Lightning Protection Measures for Cable Nets
The lightning protection of the cable network must be considered from two aspects: First, the device is subjected to lightning strike through the induction of the coaxial cable; second, when the mains lightning is struck by lightning, the pulse current caused by the abnormally high voltage causes damage to the device. Measures against damage caused by lightning protection of the cable network are:
1. Cable erection and power supply methods The coaxial cable shielded cable in the cable television system and the stranded cable for overhead support cables should have good grounding.
Every 10 poles are equipped with grounding protection. One ground wire (according to the specific resistance of the soil) can be used as a grounding body with an angle of 50mm x 50mm x 5mm of 1.5 meters long. The lightning conductor and the support strand are grounded. Tied with iron tie into one. At the same time, it is necessary to scientifically select the power supply mode of the amplifier and use centralized power supply as much as possible. Lightning is most likely to enter the electronic equipment from the power cord. Since cable TV's electronic equipment is much more tolerant to over-voltage than the power equipment, lightning arrestors must be installed on the incoming line. The power cord can be wound before entering the electronic equipment. The coils form a small inductor, which has no effect on the 50HZ current, but it has a certain effect on blocking the lightning wave from entering the equipment. When the system is grounded, it must pay attention to the minimization of the grounding resistance, and the grounding resistance has a large effect on lightning protection. It is best to reduce the grounding resistance as much as possible and control the impedance below 8Ω.
2. Lightning protection of amplifiers and branch distributors In the selection of amplifiers, amplifiers with lightning protection devices at both ends of the connector should be used as far as possible. Each amplifier box should be equipped with a lightning protection ground wire, and the grounding resistance of the ground wire should be less than 10Ω, so that lightning can be generated. The energy is released to the ground and protects the amplifier. The mains amplifier is used. The induction lightning introduced by the mains power is also prevented from damaging the amplifier. Therefore, a lightning arrester can be installed in areas where there are frequent lightning strikes. 220V The overvoltage protection device should be provided at the power supply end of the power amplifier, and the overvoltage protection is considered as an important prerequisite.
The lightning protection of cable television system is a comprehensive technical project. Taking the current understanding of the objective laws of lightning phenomena and the level of protection technology, taking the above measures can significantly reduce the frequency of lightning damage, but it cannot be completely avoided. Therefore, only by truly doing a good job in the maintenance of cable television networks will reduce the incidence and harm of lightning strikes and improve the overall benefits of the cable TV industry.
As the cable television transmission network is spread over urban and rural areas, and optical cables and cable lines span various complex terrains, it is crucial to ensure the safety and quality of cable television broadcasting. In the initial stage of building the network, it is necessary to conduct investigations and investigations, survey routings, select grounding points for grounding lines, measure the soil resistivity of the ground trenches, review the meteorological data of the past years, and understand the distribution of lightning strikes. After grasping the relevant information, the following grounding methods can be used to prevent lightning strikes.
Front-end lightning protection measures
The front end is the core of the entire cable television system. The front end includes various open-circuit antennas, satellite antennas, satellite receivers, modulator demodulators, and light-emitting devices. In the event that these devices are damaged by lightning strikes, in addition to causing serious economic losses, they will also cause a wide range of outages. Therefore, front-end lightning protection measures are very important.
There are two main types of lightning protection at the front end:
1. Lightning protection of the receiving antenna. Lightning protection measures include: A. Determining the geographical position of the receiving antenna. When installing the antenna, it is necessary to ensure the quality of the received signal and avoid the minefield. B. Add the signal lightning protector. The main function of this lightning protection device is to make The signal passes smoothly, and in the event of an abnormally high voltage caused by thunder and lightning, its internal amplification tube immediately acts to prevent the lightning from damaging the equipment; C. erecting the lightning rod, which is a universal and more effective lightning protection measure. Lightning rods should be made of high-quality metal materials with relatively large diameters. They must be buried underground and reliably grounded. The grounding resistance should be controlled within 4Ω.
2. Lightning protection of the power supply. Lightning protection measures include:
The installation of lightning protection devices will damage the equipment on the circuit when the mains generates high pulse voltage due to lightning or other factors. Therefore, install a lightning protection device in the cable television room. Its role is to release a large amount of pulse energy generated by an induced lightning strike on the safety ground in the shortest time, so as to protect the front-end equipment in the computer room.
To do work grounding, in the cable television system, the AC power used is generally provided by a low-voltage power supply network that is not grounded on the neutral line. Electrical and electronic equipment provided by this low-voltage power supply network should adopt protective grounding measures. , that is, the implementation of the work grounding, this protective grounding is the electrical equipment, metal shell, frame and other grounding device and the earth reliably connected, the working ground to ensure that the working room ground potential is zero potential, through the work ground, you can escape Leakage of equipment can also discharge static electricity generated by various friction. Lightning carried by the signal input and output cables in the equipment room and the metal protective layer of the cable is also discharged through the working ground.
Light node lightning protection
The lightning protection of the optical node is also very important. The lightning protection measures of the optical node are mainly grounding and lightning protection of the power supply. In general, the optical receiver itself has a lightning protection device, but it needs a good grounding to really work. The optical node chassis is connected with the grounding body, and the optical receiver and the power supply box are connected with the optical node chassis, and all the device housings are guaranteed. All of them are reliably grounded. The lightning protection of the power node of the optical node must be equipped with a lightning protection device to release a large amount of pulse energy generated by the utility lightning due to the induced lightning strike on the grounding body, so as to protect the electrical equipment within the optical node and achieve better performance. The lightning protection effect.
Lightning Protection Measures for Cable Nets
The lightning protection of the cable network must be considered from two aspects: First, the device is subjected to lightning strike through the induction of the coaxial cable; second, when the mains lightning is struck by lightning, the pulse current caused by the abnormally high voltage causes damage to the device. Measures against damage caused by lightning protection of the cable network are:
1. Cable erection and power supply methods The coaxial cable shielded cable in the cable television system and the stranded cable for overhead support cables should have good grounding.
Every 10 poles are equipped with grounding protection. One ground wire (according to the specific resistance of the soil) can be used as a grounding body with an angle of 50mm x 50mm x 5mm of 1.5 meters long. The lightning conductor and the support strand are grounded. Tied with iron tie into one. At the same time, it is necessary to scientifically select the power supply mode of the amplifier and use centralized power supply as much as possible. Lightning is most likely to enter the electronic equipment from the power cord. Since cable TV's electronic equipment is much more tolerant to over-voltage than the power equipment, lightning arrestors must be installed on the incoming line. The power cord can be wound before entering the electronic equipment. The coils form a small inductor, which has no effect on the 50HZ current, but it has a certain effect on blocking the lightning wave from entering the equipment. When the system is grounded, it must pay attention to the minimization of the grounding resistance, and the grounding resistance has a large effect on lightning protection. It is best to reduce the grounding resistance as much as possible and control the impedance below 8Ω.
2. Lightning protection of amplifiers and branch distributors In the selection of amplifiers, amplifiers with lightning protection devices at both ends of the connector should be used as far as possible. Each amplifier box should be equipped with a lightning protection ground wire, and the grounding resistance of the ground wire should be less than 10Ω, so that lightning can be generated. The energy is released to the ground and protects the amplifier. The mains amplifier is used. The induction lightning introduced by the mains power is also prevented from damaging the amplifier. Therefore, a lightning arrester can be installed in areas where there are frequent lightning strikes. 220V The overvoltage protection device should be provided at the power supply end of the power amplifier, and the overvoltage protection is considered as an important prerequisite.
The lightning protection of cable television system is a comprehensive technical project. Taking the current understanding of the objective laws of lightning phenomena and the level of protection technology, taking the above measures can significantly reduce the frequency of lightning damage, but it cannot be completely avoided. Therefore, only by truly doing a good job in the maintenance of cable television networks will reduce the incidence and harm of lightning strikes and improve the overall benefits of the cable TV industry.
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