Modern comprehensive lightning protection measures
can cause damage to buildings and personal injuries and deaths caused by direct lightning strikes. Their protection is to use lightning rods, straps, wires, and nets as air-termination devices to receive the lightning current, and then quickly resolve them through a good grounding device. Send it back to the earth safely. The lightning electromagnetic pulse generated by cloud-to-ground discharge and cloud-to-cloud discharge will cause some conductors on the ground to produce an induced voltage of up to thousands of volts within a certain range. They invade the equipment through various wires and metal conductors, causing equipment damage. All kinds of lightning rods can only protect against direct lightning strikes, but are powerless against lightning strikes with electromagnetic pulses. The protection of lightning electromagnetic pulse can only be effectively protected by shielding, reasonable wiring, equipotential connection, shared grounding system and installation of various surge protectors.
Modern comprehensive lightning protection technologies include:
1. Air-termination devices: use metal air-termination devices (including lightning rods, lightning protection wires, lightning protection belts, lightning protection nets), and metal roofs and metal components used for lightning protection, which are installed on the top of buildings or Make the high end higher than the top of the building, attract thunder and lightning, conduct the strong current of thunder and lightning to the earth, prevent the lightning current from passing through the building, so as to protect the building from lightning strikes, and play a role in protecting the building.
2. Down conductor: Down conductor is the metal conductor connecting the air-termination device and the grounding device. It introduces the lightning current intercepted by the air-termination device into the earth channel. The number of down conductors directly affects the effect of shunting the lightning current. If there are more wires, the lightning current passing through each down wire will be less, and its induction range and intensity will be smaller.
3. Grounding technology: Lightning protection grounding is used to lead the lightning current into the earth to prevent the lightning current from causing electric shocks or property damage.
4. Shielding technology: Shielding is a basic measure to reduce electromagnetic interference. The objects to be protected are surrounded by conductors such as metal nets, foils, shells, tubes, etc., in a physical sense, it is the channel through which the lightning pulse electromagnetic field invades from space. Block it up, and strive to “drill without gaps.” In order to reduce the electromagnetic induction effect of lightning, shielding measures are often used on the exterior of buildings and rooms, and lines are laid and shielded in appropriate paths. These measures should be used in combination.
5. Reasonable wiring: In modern buildings, the wiring of electronic equipment such as lighting, power, telephone, television and working computer must be considered. The relationship between lightning protection facilities and various pipelines must be considered. Reasonable wiring is also an important measure for lightning protection projects. In the integrated wiring of the computer room, in order to make the wiring project beautiful and beautiful, many network cables are often placed in the wall, and the shielding of the UTP cable is not considered. Once some steel bars in the building discharge lightning current, it will cause high voltage induction and damage. equipment. From the perspective of lightning protection, the power cord should not be installed in the same slot with the network cable, and the data socket should be kept a certain distance from the power socket; the WAN cable should not be installed in the same slot with the LAN cable; when the network cable is arranged with the wall, it should be installed remotely if possible ; The shielding slot requires two points to be grounded.
6. Equipotential bonding: Equipotential bonding refers to connecting separate devices and conductive objects with equipotential bonding conductors or surge protectors to reduce the potential difference between them caused by lightning current.
Equipotential bonding is an extremely critical item in lightning protection measures. The perfect equipotential connection can also eliminate the “counterattack” phenomenon caused by the sudden rise of ground potential.
7. Overvoltage protection: All wires from outdoors that cannot be directly connected by conductors (including power lines, telephone lines, signal lines, or the metal jackets of such cables, etc.) are connected to the ground through a parallel surge protector (SPD) The function of the wire is to divert the lightning overvoltage wave passing through the wire into the ground through the SPD at the SPD, which is similar to blocking all the intrusion channels of the lightning current, and not only the first-level blocking, but also the multi-level blocking.
The basic principle of lightning overvoltage protection is to establish an equipotential between all conductive parts in the protected area within a very short time of transient overvoltage. Such conductive parts include the active lines and signal transmission lines of the power supply system. . That is to say, in order to prevent the electromechanical system from being struck by lightning, a lightning current of up to tens of thousands of amperes must be transmitted from the power transmission line and the signal transmission line to the ground in a very short time.
The above measures should be used in a comprehensive manner, and it is imperfect to adopt one or a few of these technologies alone. For lightning protection, there are still loopholes.