In our country, the number of casualties caused by lightning strikes is estimated to be 3,500 to 4,000 people each year, and the property loss is estimated to be about 7 to 10 billion yuan. Therefore, before understanding the lightning protection products, we may wish to make some understanding of the lightning protection knowledge so that we may have the necessary correct understanding in the purchase and use.
One, lightning strike
Thunder is a discharge phenomenon in the atmosphere. There are mainly two kinds of lightning strikes: direct lightning and induced lightning. Among them, direct strike lightning accounts for only about 10% of the lightning strike, and the scope of harm is relatively small. In CATV systems and networks, lightning rods, lightning conductors, and lightning protection nets are commonly used for protection; and the most inductive induction mines account for 90% of the lightning stroke rate, and the scope of harm Wide, it is difficult to effectively protect, most of the electronic devices are mainly caused by lightning and lightning damage.
1. Direct lightning strikes and hazards: Direct lightning strikes are caused by discharges between charged cloud layers and the earth. In the procedure for forming thunderclouds, some clouds show a positive charge and gradually increase the potential; other clouds are negatively charged. When the two clouds approach to a certain degree, a rapid and intense discharge occurs. The discharge temperature can reach as high as 20,000 degrees. The air expands rapidly due to heat, and each discharge discharges considerable energy in approximately a few microseconds. When the thundercloud is very low and there are no other thunderclouds with other opposite charges around it, an opposite-pole charge will be induced in the building or on the ground. This will cause the charged cloud layer to discharge to the ground or buildings. This kind of lightning is a direct lightning strike. Buildings and people, livestock, trees and other hazards are huge, because at this time the discharge current can reach tens or even several hundred kiloamperes, the discharge time is very short, simply can not avoid, the commonly used lightning rod method is to reduce the direct damage of direct lightning damage is better The protection method, but the user often found in the actual work after the direct thunder, many electronic devices still have greater damage, most of the burned fuse devices, power transformers, rectifier devices, and even integrated circuits. What causes this? This is caused by the induction of lightning, which causes damage through the power transfer device of the CATV system.
2. The generation and damage of the induced lightning: The induced lightning is caused by two reasons: the electrostatic reactor and the electromagnetic induction caused by the lightning current. When the charged lightning cloud is close to the transmission line, opposite charges will be induced on the line. The charge is bound by the thundercloud charge. When the thundercloud discharges to the nearby field or the air-termination device, its charge is quickly neutralized. At this time, the bound charge on the transmission line becomes a free charge, forming a local induced high potential. The high level of induction occurs at up to 100KV on low-voltage overhead lines and 40-60KV on telecommunication lines. And it can extend the line into various electronic devices to cause damage, and the main cause of damage is electromagnetic induction. Electromagnetic induction is a phenomenon in which a large lightning current after a lightning strike generates an alternating magnetic field in the surrounding space and causes a high-voltage damage device in the vicinity of the mine field device. The lightning current of a lightning-inducing current (from zero to straight) is usually a few seconds, and the wave tail is also several tens of microseconds, but the lightning current of the induced lightning contains rich higher harmonics, and its fundamental frequency is approximately equal to Dozens of kilohertz. Therefore, the protection of inductive lightning has been plaguing users of various types of electronic devices, especially users of various system networks used in field environments, such as power lines, communication lines, cable television lines, and monitoring system lines. Broadband data network systems, etc., are therefore most vulnerable to induced lightning.
Second, the principle of the destruction of lightning
The mechanical force of the lightning current can cause the object to be damaged. The principle of lightning damage is mainly reflected in the following aspects:
1, lightning current thermal effect of the principle of destruction: Lightning hit the ground object, lightning current Joule - Yuji thermal effect, although the peak current is high, but the role of time is very short, can only produce local transient high temperature, strong lightning current through Lightning strikes objects that produce very high temperatures that melt, vaporize, or burn, allowing smaller volumes of metal to melt. In the attack phase, the peak discharge of Thundercloud to ground can reach more than 105A and the instantaneous power can reach more than 1011W. At this moment, it will cause a strong heating effect on its channel, and the air temperature in the discharge channel can rise to 30000 degrees instantaneously. As a result, when a flammable substance is encountered on the passageway, a fire will occur.
2, the principle of destruction of lightning current shock wave: As the air in the lightning channel is heated to expand rapidly, and spread to the surrounding area at ultrasonic speed, the cold air near the periphery is strongly compressed to form a "shock wave". The outside of the compressed air is called "shock wave front". Where the “shock wave†arrives, the air density, pressure, and temperature suddenly increase. After the “shock wave frontâ€, the air pressure in the area fell until it was below atmospheric pressure. Such "shock waves" spread in the air, causing damage to nearby buildings and humans and animals as well as injuries to nearby buildings, people and livestock. Thunderclouds in the process of contraction after discharge, due to the sudden contraction of lightning, but also produce infrasound waves, it also has a harmful effect on people and livestock.
3. The principle of destruction of the electro-dynamic effect of lightning currents: Since the peak value of the lightning current is very large and the action time is very short, the resulting electromotive force has an impulse characteristic. This electromotive force has a greater destructive effect on metal conductors.
4. Principles of electrostatic induction and electromagnetic induction destruction of lightning: Lightning produces a powerful mechanical effect and heating effect at the return passage and its close proximity. At the same time, it also produces an electromagnetic effect that can spread farther away. The harmfulness of this electromagnetic wave leads to A large number of electronic devices are damaged and interrupted.
(1) Electrostatic induction: When there are charged lightning clouds in the space, the ground and buildings under the thundercloud are charged with opposite charges due to electrostatic induction. In the event of a lightning strike, the charge carried on the thundercloud quickly neutralizes the alien charge of the ground by the flash strike. Some local parts, such as the induced current on the overhead conductor, cannot withstand the same short time due to the large resistance between the ground and the earth. Disappearing, this creates a local induced high voltage. This induction high voltage can reach 300-400KV on high-voltage overhead lines, 100KA on low-voltage overhead lines, 4-60KV on telecommunication lines, and 20-40KV on cable television lines, on buildings. It can also generate a rather high dangerous voltage. This overvoltage due to electrostatic induction not only damages the poorly grounded electrical system, but also causes the occurrence of sparks between the metal frame and the poorly grounded metal parts, and places or places where flammable or explosive materials are stored. , causing a fire or explosion.
(2) Electromagnetic induction: Due to the extremely large peak and steepness of the lightning current, there is a powerful changing electromagnetic field in the space around it, and the conductor in this electromagnetic field will induce a large electromotive force. This electromagnetic induction can also cause flammable fires and explosions.
5. Lightning counterattack and the introduction of high potential (1), lightning counterattack, direct lightning hit the metal body (including the air-termination device, grounding lead and grounding body), the metal body in the moment of lightning and the ground there is a high voltage, This voltage will strike the other metal objects connected to the earth.
(2) When lightning is introduced into a high potential, when a lightning strike or inductive lightning is introduced into a building from a lead-in line such as a transmission line, a communication cable, or a radio antenna, an accidental lightning strike may occur.
3. Lightning Invasion Route 1. When a lightning strikes a building, the lightning energy is transmitted along the power supply line, the communication line, the network line through potential counterattacks, various coupling mechanisms (current coupling, inductive coupling, capacitive coupling), and electromagnetic pulse radiation. Metal pipes enter the equipment, causing damage to the equipment. Within a radius of 1.5~3km from the center of the lightning strike, lightning electromagnetic pulses radiate radiation along the various lines and enter the equipment.
2. When a lightning strike occurs on the high voltage transmission line, the overvoltage generated on the line will also be transmitted along the line until the low side of the transformer, causing damage to the equipment.
3. The discharge between thunderclouds and thunderclouds will also generate lightning surges and enter the equipment through various metal conductor lines.
4, clouds charged, so that a building on the surface of a building or long wire induction with a different charge, resulting in surge into the device.
Fourth, the lightning protection zones <br> <br> according to GB50343 "Building an electronic information system lightning protection technical specifications", according to the building space needed protection from outside to inside is divided into different lightning protection zone: non-direct lightning protection zone (LPZOA), direct strike protection zone (LPZOB), first protection zone (LPZ1), second protection zone (LPZ2), and subsequent protection zone (LPZn). As shown in Figure 5-2.
The practical significance of lightning protection partitions:
1. It is possible to calculate the intensity of the spatial lightning electromagnetic pulse in each LPZ to confirm whether further shielding measures are needed.
2. The position of the equipotential bonding can be determined (usually at the junction of each LPZ zone).
3. The specific indicators for selecting surge protectors at the junction of different LPZs can be determined.
4. You can select the safe placement of sensitive electronic devices.
5. The minimum core cross section of the equipotential bonding conductor at the interface of different LPZs can be determined.
V. How to prevent lightning 1. Integrated lightning protection design Modern lightning protection technology is an integrated system engineering. The more reasonable the system structure is, the more reasonable the organic combination among the various components (or elements) of the system will be. The more coordination, the overall system to achieve the best operating status.
The building integrated lightning protection device is divided into two major parts: an external lightning protection device and an internal lightning protection device. In the lightning protection design, the external lightning protection device and the internal lightning protection device must be taken into consideration as a whole.
2. System lightning protection design as a system, lightning protection for the power and signal of the electrical equipment, electrical appliances, and electronic equipment (including the power supply and distribution room, engine room and power supply, equipment room equipment, line equipment, etc.) used in the entire system, It needs to be considered from the overall system protection, security and standardization.
3. Single-unit lightning protection As a single device, a single consideration and design can be made from the specific technical requirements of the device.
One, lightning strike
Thunder is a discharge phenomenon in the atmosphere. There are mainly two kinds of lightning strikes: direct lightning and induced lightning. Among them, direct strike lightning accounts for only about 10% of the lightning strike, and the scope of harm is relatively small. In CATV systems and networks, lightning rods, lightning conductors, and lightning protection nets are commonly used for protection; and the most inductive induction mines account for 90% of the lightning stroke rate, and the scope of harm Wide, it is difficult to effectively protect, most of the electronic devices are mainly caused by lightning and lightning damage.
1. Direct lightning strikes and hazards: Direct lightning strikes are caused by discharges between charged cloud layers and the earth. In the procedure for forming thunderclouds, some clouds show a positive charge and gradually increase the potential; other clouds are negatively charged. When the two clouds approach to a certain degree, a rapid and intense discharge occurs. The discharge temperature can reach as high as 20,000 degrees. The air expands rapidly due to heat, and each discharge discharges considerable energy in approximately a few microseconds. When the thundercloud is very low and there are no other thunderclouds with other opposite charges around it, an opposite-pole charge will be induced in the building or on the ground. This will cause the charged cloud layer to discharge to the ground or buildings. This kind of lightning is a direct lightning strike. Buildings and people, livestock, trees and other hazards are huge, because at this time the discharge current can reach tens or even several hundred kiloamperes, the discharge time is very short, simply can not avoid, the commonly used lightning rod method is to reduce the direct damage of direct lightning damage is better The protection method, but the user often found in the actual work after the direct thunder, many electronic devices still have greater damage, most of the burned fuse devices, power transformers, rectifier devices, and even integrated circuits. What causes this? This is caused by the induction of lightning, which causes damage through the power transfer device of the CATV system.
2. The generation and damage of the induced lightning: The induced lightning is caused by two reasons: the electrostatic reactor and the electromagnetic induction caused by the lightning current. When the charged lightning cloud is close to the transmission line, opposite charges will be induced on the line. The charge is bound by the thundercloud charge. When the thundercloud discharges to the nearby field or the air-termination device, its charge is quickly neutralized. At this time, the bound charge on the transmission line becomes a free charge, forming a local induced high potential. The high level of induction occurs at up to 100KV on low-voltage overhead lines and 40-60KV on telecommunication lines. And it can extend the line into various electronic devices to cause damage, and the main cause of damage is electromagnetic induction. Electromagnetic induction is a phenomenon in which a large lightning current after a lightning strike generates an alternating magnetic field in the surrounding space and causes a high-voltage damage device in the vicinity of the mine field device. The lightning current of a lightning-inducing current (from zero to straight) is usually a few seconds, and the wave tail is also several tens of microseconds, but the lightning current of the induced lightning contains rich higher harmonics, and its fundamental frequency is approximately equal to Dozens of kilohertz. Therefore, the protection of inductive lightning has been plaguing users of various types of electronic devices, especially users of various system networks used in field environments, such as power lines, communication lines, cable television lines, and monitoring system lines. Broadband data network systems, etc., are therefore most vulnerable to induced lightning.
Second, the principle of the destruction of lightning
The mechanical force of the lightning current can cause the object to be damaged. The principle of lightning damage is mainly reflected in the following aspects:
1, lightning current thermal effect of the principle of destruction: Lightning hit the ground object, lightning current Joule - Yuji thermal effect, although the peak current is high, but the role of time is very short, can only produce local transient high temperature, strong lightning current through Lightning strikes objects that produce very high temperatures that melt, vaporize, or burn, allowing smaller volumes of metal to melt. In the attack phase, the peak discharge of Thundercloud to ground can reach more than 105A and the instantaneous power can reach more than 1011W. At this moment, it will cause a strong heating effect on its channel, and the air temperature in the discharge channel can rise to 30000 degrees instantaneously. As a result, when a flammable substance is encountered on the passageway, a fire will occur.
2, the principle of destruction of lightning current shock wave: As the air in the lightning channel is heated to expand rapidly, and spread to the surrounding area at ultrasonic speed, the cold air near the periphery is strongly compressed to form a "shock wave". The outside of the compressed air is called "shock wave front". Where the “shock wave†arrives, the air density, pressure, and temperature suddenly increase. After the “shock wave frontâ€, the air pressure in the area fell until it was below atmospheric pressure. Such "shock waves" spread in the air, causing damage to nearby buildings and humans and animals as well as injuries to nearby buildings, people and livestock. Thunderclouds in the process of contraction after discharge, due to the sudden contraction of lightning, but also produce infrasound waves, it also has a harmful effect on people and livestock.
3. The principle of destruction of the electro-dynamic effect of lightning currents: Since the peak value of the lightning current is very large and the action time is very short, the resulting electromotive force has an impulse characteristic. This electromotive force has a greater destructive effect on metal conductors.
4. Principles of electrostatic induction and electromagnetic induction destruction of lightning: Lightning produces a powerful mechanical effect and heating effect at the return passage and its close proximity. At the same time, it also produces an electromagnetic effect that can spread farther away. The harmfulness of this electromagnetic wave leads to A large number of electronic devices are damaged and interrupted.
(1) Electrostatic induction: When there are charged lightning clouds in the space, the ground and buildings under the thundercloud are charged with opposite charges due to electrostatic induction. In the event of a lightning strike, the charge carried on the thundercloud quickly neutralizes the alien charge of the ground by the flash strike. Some local parts, such as the induced current on the overhead conductor, cannot withstand the same short time due to the large resistance between the ground and the earth. Disappearing, this creates a local induced high voltage. This induction high voltage can reach 300-400KV on high-voltage overhead lines, 100KA on low-voltage overhead lines, 4-60KV on telecommunication lines, and 20-40KV on cable television lines, on buildings. It can also generate a rather high dangerous voltage. This overvoltage due to electrostatic induction not only damages the poorly grounded electrical system, but also causes the occurrence of sparks between the metal frame and the poorly grounded metal parts, and places or places where flammable or explosive materials are stored. , causing a fire or explosion.
(2) Electromagnetic induction: Due to the extremely large peak and steepness of the lightning current, there is a powerful changing electromagnetic field in the space around it, and the conductor in this electromagnetic field will induce a large electromotive force. This electromagnetic induction can also cause flammable fires and explosions.
5. Lightning counterattack and the introduction of high potential (1), lightning counterattack, direct lightning hit the metal body (including the air-termination device, grounding lead and grounding body), the metal body in the moment of lightning and the ground there is a high voltage, This voltage will strike the other metal objects connected to the earth.
(2) When lightning is introduced into a high potential, when a lightning strike or inductive lightning is introduced into a building from a lead-in line such as a transmission line, a communication cable, or a radio antenna, an accidental lightning strike may occur.
3. Lightning Invasion Route 1. When a lightning strikes a building, the lightning energy is transmitted along the power supply line, the communication line, the network line through potential counterattacks, various coupling mechanisms (current coupling, inductive coupling, capacitive coupling), and electromagnetic pulse radiation. Metal pipes enter the equipment, causing damage to the equipment. Within a radius of 1.5~3km from the center of the lightning strike, lightning electromagnetic pulses radiate radiation along the various lines and enter the equipment.
2. When a lightning strike occurs on the high voltage transmission line, the overvoltage generated on the line will also be transmitted along the line until the low side of the transformer, causing damage to the equipment.
3. The discharge between thunderclouds and thunderclouds will also generate lightning surges and enter the equipment through various metal conductor lines.
4, clouds charged, so that a building on the surface of a building or long wire induction with a different charge, resulting in surge into the device.
Fourth, the lightning protection zones <br> <br> according to GB50343 "Building an electronic information system lightning protection technical specifications", according to the building space needed protection from outside to inside is divided into different lightning protection zone: non-direct lightning protection zone (LPZOA), direct strike protection zone (LPZOB), first protection zone (LPZ1), second protection zone (LPZ2), and subsequent protection zone (LPZn). As shown in Figure 5-2.
The practical significance of lightning protection partitions:
1. It is possible to calculate the intensity of the spatial lightning electromagnetic pulse in each LPZ to confirm whether further shielding measures are needed.
2. The position of the equipotential bonding can be determined (usually at the junction of each LPZ zone).
3. The specific indicators for selecting surge protectors at the junction of different LPZs can be determined.
4. You can select the safe placement of sensitive electronic devices.
5. The minimum core cross section of the equipotential bonding conductor at the interface of different LPZs can be determined.
V. How to prevent lightning 1. Integrated lightning protection design Modern lightning protection technology is an integrated system engineering. The more reasonable the system structure is, the more reasonable the organic combination among the various components (or elements) of the system will be. The more coordination, the overall system to achieve the best operating status.
The building integrated lightning protection device is divided into two major parts: an external lightning protection device and an internal lightning protection device. In the lightning protection design, the external lightning protection device and the internal lightning protection device must be taken into consideration as a whole.
2. System lightning protection design as a system, lightning protection for the power and signal of the electrical equipment, electrical appliances, and electronic equipment (including the power supply and distribution room, engine room and power supply, equipment room equipment, line equipment, etc.) used in the entire system, It needs to be considered from the overall system protection, security and standardization.
3. Single-unit lightning protection As a single device, a single consideration and design can be made from the specific technical requirements of the device.
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