What are the main measures of modern lightning protection technology (air-termination device)?
Modern lightning protection technologies include external lightning protection and internal lightning protection. External lightning protection refers to the implementation of lightning protection measures on the outside of the building, intercepting lightning outside the building, so that people, animals and buildings are protected from lightning strikes.
Internal lightning protection refers to the implementation of lightning protection measures in various ways that may transmit and induce lightning, intercept the damage of lightning to electronic equipment and electrical systems in buildings, and protect people and electrical equipment.
Modern lightning protection technical measures can be simply boiled down to the seven letters of ABCDGS. Hide: Avoid, Equipotential Connection: Bonding, To: Conducting, Shunt: Dividing, Grounding: Grounding, Shielding: Shielding.
1. It is a very important economical and effective measure to adopt "hiding" measures in modern lightning protection engineering technology. There is another kind of "hiding" that is positive. This is to consider lightning protection in the site selection and planning of the building, avoiding mine areas or places prone to lightning. This can reduce the cost of lightning protection and avoid getting into trouble in the future.
2. Equipotential bonding, from the perspective of physics, is to weld various metal objects with thick wires, or weld them directly to ensure that the points are equal. The perfect equipotential connection can also eliminate the "counterattack" phenomenon caused by the sudden rise of equipotential, which is often encountered after a microwave station antenna tower is struck by lightning.
3. The function of conduction is to guide the huge energy of lightning to the large underground to dissipate it. Of course, other methods can also be studied to absorb and dissipate its energy so that it cannot cause damage to the object to be protected.
4. The function of shunting is to divert the overvoltage wave introduced along the wire into the ground through the arrester at the lightning arrester, which is similar to intercepting all the intrusion channels of lightning current, and more than one level of interception, multi-level interception.
5. Grounding is the leakage of lightning energy into the ground. Although grounding measures are the basis of lightning protection measures, without it, the three lightning protection measures of equipotential connection, conduction and shunting cannot achieve the expected effect. , Whether the grounding is proper or not is a link that is particularly valued in lightning protection technology. Various lightning protection specifications have made clear provisions on grounding measures. It is also the focus and difficulty of lightning protection engineering, and the main work of lightning protection device safety inspection is carried out around it.
6. Shielding means that metal nets, foils, tubes and other conductors wrap the objects that need to be protected. In a physical sense, it is to intercept the passage of lightning pulse electromagnetic field from space intrusion, and strive to be "seamlessly drillable."
All kinds of shielding must be properly grounded, so the five measures "BCDGS" is an organically linked overall lightning protection system, and a complete implementation can achieve a foolproof effect.
What is an air-termination device? What are the commonly used air-termination devices in lightning protection projects?
The metal conductor used to intercept current is what people call an air-termination device. Commonly used lightning rods, lightning cables, lightning belts and lightning nets. Sometimes the large metal frame on the top of the building is also used as an air-termination device. These non-dedicated metal conductors that can be used as air-termination devices are also called natural air-termination devices.
In lightning protection projects, one type of lightning rod can often be used as needed. For example, some lightning protection buildings often need to install independent lightning rods, or a combination of two types of lightning rods, such as lightning rods and lightning belts or lightning rods and lightning nets. Combination etc.
Which parts of the building can be used as natural air-termination devices?
The following components related to buildings can be used as natural air-termination devices:
1. Cover the metal plate that needs lightning protection space. The metal plate should meet the following requirements:
There is a reliable electrical connection between the metal plates;
When it is necessary to prevent the metal plate from being broken down by lightning (perforation or hot spot), the thickness of the metal plate shall not be less than steel: 4mm, copper: 5mm, and aluminum: 7mm;
When it is not necessary to prevent the metal plate from being penetrated by lightning or ignite the combustibles under the metal plate, the thickness of the metal plate is not less than 0.5mm;
The metal plate has no insulation covering layer;
Non-metallic materials on or above the metal plate can be excluded from the space that needs lightning protection.
2. When the non-metal roof can be excluded from the lightning protection space, the metal parts of the roof structure below it.
3. The cross-section of drain pipes, decorations, railings and other metal parts of the building shall not be less than the cross-section specified by the corresponding standard air-termination parts.
4. Metal pipes and metal cans with a thickness of not less than 2.5mm, and there will be no danger or other unacceptable conditions during lightning breakdown.
5. Metal cans and pipes with a thickness of not less than steel: 4mm, copper: 5mm, and aluminum: 7mm, and the temperature rise of the inner surface of the lightning strike is not a danger.