Basic knowledge of lightning protection and grounding safety

 1. There are two basic forms of lightning overvoltage:
The first is: direct lightning-also known as direct lightning
Second is: Lightning induction-also known as induction lightning
 2. The role of the air-termination device:
The lightning receptor is a metal body used to receive direct lightning strikes. It must be connected to the grounding device through a grounding lead.
3. Lightning rod function:
The function of the lightning rod is actually to lead the mine, it is used to protect against direct lightning.
4. Types and functions of arresters:
Generally used surge arresters are valve type, exhaust type (tube type), zinc oxide, etc.
Lightning arresters are used to protect lightning overvoltages from entering the substation or other buildings along the line to avoid endangering the insulation of the protected objects. At present, zinc oxide arresters are often used outdoors in power distribution, and valve type arresters are often used indoors.
5. Lightning protection measures commonly used in transformer substations:
Protection against lightning strikes The use of lightning rods (or lightning rods, lightning strips, and lightning protection nets) to prevent the intrusion of lightning waves is a lightning arrester.
6. Concept of safe current:
Safe current refers to the maximum shed current after an electric shock. The safe current specified by our country is 30 mA (50HZ). Safe current is related to factors such as the time of electric shock, the nature of the current, the current path, and weight and health.
7. Safe voltage concept:
Safe voltage refers to a voltage that does not cause death or disability directly. The safety extra-low voltage required by China is 36 volts.
 8. Concept of land:
Electrical ground (or earth) refers to the place where the potential is zero; this ground generally refers to a place about 20 meters away from the ground fault point.
 9. Contact voltage, step voltage:
Contact voltage refers to the voltage to ground when people are in contact with the exposed conductive part of the equipment where the ground fault occurs. Step voltage refers to the potential difference between the two feet when people walk near the ground fault point.
10. Concepts of working ground and protective ground:
的 The grounding to ensure that the power system and equipment meet the requirements of normal work is called working grounding.
的 The grounding for personal safety and protection against indirect contact is called protective grounding.
For example: the neutral ground of the transformer, the ground of the lightning arrester and the arrester are working grounds. The grounding of the secondary terminal of the transformer and the grounding of the equipment case are protective grounding.
11. Several protective grounding methods currently used in China:
There are TN system, TT system, IT system.
In the TN system, it is divided into three types of protective grounding: TN-C, TN-S, TN-C-S.
12. Equipotential bonding: Equipotential bonding can be divided into total equipotential bonding and auxiliary equipotential bonding.
The purpose of this method is to directly connect conductive metal objects that people may come in contact with PE wire. Internationally and in China, it is stipulated that the equipotential connection should be implemented at the entrance of the power line, that is, all metal components and pipes near the entrance of the power line are connected to the PE line. In particularly humid and dangerous places (such as bathrooms), auxiliary equipotential bonding must be performed, that is, all metal components and pipes in the place are connected with PE wires.
13. The first thing to do when someone is shocked is to find a way to get the shocked person out of the power supply quickly, and then perform other first aid.

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Mar. 16, 2020