1、 How is lightning formed?

Answer: Lightning is an atmospheric discharge phenomenon that occurs during the formation of cumulonimbus clouds. Some cloud clusters carry positive charges, while others carry negative charges. They induce static electricity on the ground, causing opposite charges to be generated on the surface of the ground or buildings. When the charges accumulate to a certain extent, the electric field strength between different charge clouds or between clouds and the ground can penetrate the air (usually 25-30KV/cm) and begin to discharge freely, which we call 'lead discharge'. The leading discharge from the cloud to the ground gradually develops as the cloud jumps towards the ground. When it reaches the ground (buildings, overhead power lines, etc. on the ground), a reverse leading main discharge from the ground to the cloud cluster will occur. In the main discharge stage, due to the intense neutralization of opposite charges, there will be a large lightning current (usually tens to hundreds of kiloamperes), accompanied by strong lightning and loud noise, which forms lightning.

2、 What is step voltage?

Answer: Step voltage is when lightning strikes a ground object, causing the lightning current to leak into the ground and disperse in the soil. Due to the distribution of soil resistivity, the lightning current experiences a potential drop between different points on the ground. The closer the lightning strike point is, the higher the current density, the greater the potential drop. If a person stands or walks near a lightning point, the potential drop between their feet can cause lightning current to pass through their feet and lower body, resulting in injury. The potential drop between these two feet is called 'step voltage'.

3、 Why is the distance between the installed independent lightning rod (including its lightning grounding device) and the protected building at least 3 meters in a type of lightning protection.

Answer: In order to prevent the independent needle from retaliating against the protected object in the event of a direct lightning strike. 4、 What is a pressure equalization ring? What are the requirements for the design of the equalizing ring in building lightning protection design?

Answer: The equalizing ring is a horizontal lightning protection belt designed around high-rise buildings to prevent side lightning strikes. In architectural design, when the height exceeds the radius of the rolling ball (30 meters for Class I, 45 meters for Class II, and 60 meters for Class III), a pressure equalization ring should be installed every 6 meters. In terms of design, the equalizing ring can be welded into a closed loop using two main bars inside the ring beam, which must be connected to all down conductors. It is required to install a pressure equalization ring every 6 meters to facilitate the connection between the metal doors and windows on the upper and lower floors within a height of 6 meters and the pressure equalization ring.

5、 What are the requirements for down conductors and overhead grids in various lightning protection measures?

Answer: The down conductor and overhead grid are usually made of galvanized round steel with a diameter of not less than 8.

1、 The distance between the second and third types of corresponding down conductors shall not exceed 12 meters, 18 meters, and 25 meters;

1、 The corresponding sky grids for categories 2 and 3 are 5 * 5 square meters (4 * 6 square meters), 10 * 10 square meters (8 * 12 square meters), and 20 * 20 square meters (16 * 24 square meters).

6、 What methods should be used to reduce the grounding resistance of lightning protection grounding devices in areas with high soil resistivity?

Answer: According to Article 4.3.4 of Specification P26, in areas with high soil resistivity, one of the following methods can be used to reduce grounding resistance:

(1) Adopting a multi branch external grounding device, the external length shall not exceed the effective length, i.e. le=2 ρ.

(2) The grounding body is buried deep in low resistivity soil.

(3) Use drag reducing agents. (4) Change the soil.

7、 What is the phenomenon of lightning counterattack? How to eliminate the phenomenon of counterattack?

Answer: The phenomenon of lightning counterattack usually refers to the phenomenon of metal objects (including lightning arresters, grounding down conductors, and grounding bodies) that are directly struck by lightning. At the moment of lightning, there is a high voltage between them and the ground, which causes discharge (also known as flashover) to other metal objects connected to the ground. This phenomenon is called counterattack. In addition, when lightning strikes trees, there will be counterattacks between the high voltage on the trees and nearby houses and metal objects. To eliminate the phenomenon of counterattack, two measures are usually taken: one is to make equipotential connection, connecting two metal conductors together with a metal conductor to make their potential equal when flashing; The second is to maintain a certain distance between the two.

8、 What are the requirements for metal oil tanks to prevent direct lightning strikes?

Answer: Requirements for metal oil tanks in terms of direct lightning protection: (1) Oil tanks storing flammable and combustible materials should be equipped with direct lightning protection facilities (such as installing lightning rods) when the metal wall thickness is less than 4 millimeters; (2) When the metal wall thickness of oil tanks storing flammable and combustible materials is ≥ 4 millimeters, direct lightning protection facilities may not be installed. However, in areas with multiple lightning strikes, direct lightning protection facilities may also be considered. (3) The breathing valve and safety valve of the fixed top metal oil tank must be equipped with flame arresters. (4) All metal oil tanks must be equipped with circular lightning protection grounding, with no less than two grounding points and a distance of no more than 30 meters between them. The distance between the grounding body and the tank wall should be greater than 3 meters. (5) When the tank is equipped with lightning rods or used as a lightning arrester, the grounding impulse resistance shall not exceed 10 ohms.

9、 What materials are commonly used for cathodic protection devices? Why?

Answer: Cathodic protection devices are usually made of magnesium alloy or zinc alloy. Because magnesium alloy or zinc alloy is a more active metal element than iron, when a specially processed magnesium alloy or zinc alloy block is connected to a protected metal (iron) storage tank, the negative ions of the magnesium alloy or zinc alloy continuously move towards the buried metal storage tank through the connecting conductor, causing the metal storage tank to receive a certain amount of negative ions of the magnesium alloy or zinc alloy and become the cathode, while the magnesium alloy or zinc alloy continuously loses negative ions, displaying the characteristics of the anode. It is precisely because these relatively active negative ions of magnesium or zinc continuously move towards the metal storage tank, compensating for the corrosion of the tank. After years of use, magnesium alloys or zinc alloys lose their anti-corrosion ability and sacrifice themselves, so this device is also called sacrificial magnesium (zinc) anode, a device that protects the cathode (tank).

10、 What are the components of lightning protection measures?

Answer: It mainly includes three parts: direct lightning protection, side lightning protection, and induced lightning protection, and adopts technical measures such as lightning protection, current diversion, shielding, voltage equalization, equipotential, and grounding.