lightning rod

1. The role of lightning rod

Conventional lightning protection can be divided into direct lightning protection, induction lightning protection and comprehensive lightning protection. Lightning protection devices to prevent direct lightning strikes are generally composed of three parts, namely lightning rods, down conductors and grounding bodies; lightning rods, lightning cables, lightning belts, and lightning nets. The principle of lightning protection using lightning rods as air-termination devices is: the lightning rods are connected to the ground through a wire, forming an equipotential difference with the ground, and using their own height, the electric field of the lightning cloud with the electric field strength increased to the limit value will be distorted, and begin to ionize and go down. Leading discharge; the lightning rod produces a sharp discharge under the action of a strong electric field, forming an upward lead discharge; the two converge to form a lightning path, and then flow into the earth to achieve the lightning protection effect. In fact, the lightning rod is a lightning rod, which can attract the surrounding lightning and discharge it in advance, and transmit the lightning current to the ground through its own grounding conductor to avoid direct lightning strikes.

2. Attention to the installation of lightning rod

(1) There should be no less than 5m between the independent lightning rod and the protected object to avoid counterattack when lightning strikes the lightning rod. An independent grounding device should be provided for the independent lightning rod, and the distance between the ground and the grounding grid shall not be less than 3m.

(2) Lightning rods should not be installed on the frame and roof of high-voltage power distribution devices of 35kV and below. The lightning rod installed on the frame should be connected to the grounding grid, and a centralized grounding device should be installed.

(3) Lightning rods should not be installed on the door frame of the transformer.

(4) The distance between the lightning rod and the grounding device from the road and the exit should be greater than 3m, otherwise the gravel or asphalt surface should be 5-8cm thick to protect the person from the step voltage hazard.

(5) It is strictly forbidden to install overhead lighting lines, telephone lines, broadcasting lines, antennas, etc. on lightning rods or structures.

(6) If a lighting lamp is installed on an independent lightning rod or frame, the power cord must use lead-covered cables or penetrate steel pipes, and be directly buried in the ground with a length of more than 10m.

3.purchase

1. Reasonably choose the calculation method of lightning rod protection range

Common methods for calculating the protection range of lightning rods (here only refers to single needles) include the broken line method and the rolling ball method. The main feature of the "broken line method" is that the design is intuitive, the calculation is simple, and investment can be saved, but it is not suitable for buildings with a height greater than 20m; the main feature of the "rolling ball method" is that it can calculate the lightning rod or lightning strip and the grid combination The scope of protection, but the calculation is relatively complicated, and the investment cost calculated by this method is relatively large.

Among the two calculation methods, the "broken line method" is a relatively mature method. In the power system, it is also called the "regulation method", that is, the protection range of a single lightning rod is a broken line cone with the lightning rod as the axis. The protection range of a single lightning rod is stipulated in the standard DL/T620-997 "Overvoltage Protection and Insulation Coordination of AC Electrical Installations"; "Rolling Ball Method" is the calculation of the protection range of air-termination devices recommended by the International Electrotechnical Commission (IEC) One of the methods. my country's building lightning protection code GB50057-1994Z also compulsorily adopts the "rolling ball method" as a method for calculating the protection range of lightning rods. The rolling ball method is to roll a sphere with hR as the radius along the part that needs to prevent lightning strikes. When the sphere only touches the air-termination device (including the metal object used as the air-termination device) or only touches the air-termination device and the ground (including the When the earth touches the metal object that can withstand lightning strikes), but does not touch the part that needs protection, the part will be protected by the lightning receptor. In recent years, the “rolling ball method” stipulated in the national standard has also begun to be recognized by the industry. However, the “rolling ball method” has also encountered some problems in actual application, especially when calculating the protection range of the sky lightning rod. In general, these two algorithms have their own characteristics, and generally high-rise buildings use the "rolling ball method".

2. Can I use the lightning rod in advance to discharge it?

In fact, no lightning protection equipment is foolproof. It is not that there is no lightning strike in the protection range, but the lightning energy is small. From an economic point of view, it would be very wasteful to be foolproof. Therefore, the "Code for Design of Building Lightning Protection" and other design codes and standards have already "reduced" lightning strikes. Therefore, lightning protection devices designed in accordance with national and international standards are not 100% safe. In addition to direct lightning strikes, high-rise buildings may also be affected by side strikes and induced lightning.

There are two main advantages of pre-discharging a lightning rod. One is that it can "discharge in advance" and has better lightning performance than ordinary lightning rods. The second is to convert its advance discharge time into advance discharge distance, which is equivalent to increasing the height of the lightning rod, thereby increasing the protection radius. But there is still no way to protect against side lightning and induction lightning.

3. It is important to ensure the discharge capacity of the lightning rod

Various lightning protection regulations require that the lightning rod have an independent down-lead ground, which can ensure that the lightning current quickly leaks into the ground. When purchasing, don't listen to the suggestions of some irregular manufacturers, and connect the lightning rod to the grounding system of the building itself to save costs.

4. It is very important to choose a regular lightning protection manufacturer

Lightning rods are actually lightning rods, so lightning protection projects need to undergo rigorous scientific calculations. A little carelessness may lead to lightning. Therefore, when choosing a lightning rod supplier, you need to check whether it has a professional design qualification for lightning protection engineering and a professional construction qualification for lightning protection engineering. The domestic lightning rod market is a mixed bag. Some distributors who represent foreign brands advertise that their products meet advanced foreign standards. It is difficult to distinguish between true and false. It is recommended to inspect products in accordance with national standards and IEC standards when purchasing.