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Basic knowledge of lightning protection and grounding safety

1. There are two basic forms of lightning overvoltage:
One is: direct lightning – also known as direct lightning
Second: lightning induction – also known as inductive lightning
2. Function of lightning arrester:
The lightning arrester is a metal body used to accept direct lightning strike. It must be connected with the grounding device through the grounding down lead.
3. Functions of lightning rod:
The function of lightning rod is actually to lead lightning. It is used to protect against direct lightning.
4. Type and function of lightning arrester:
Commonly used lightning arresters include valve type, exhaust type (pipe type), zinc oxide, etc.
Lightning arrester is used to protect the lightning overvoltage from invading into the power transformation and distribution room or other buildings along the line, so as not to endanger the insulation of the protected object. At present, zinc oxide arrester is often used outside the distribution room, and valve arrester is usually used indoors.
5. Lightning protection measures commonly used in power transformation and distribution room of the factory:
Lightning rod (or lightning wire, lightning strip and lightning network) is used to protect against lightning wave intrusion.
6. Concept of safe current:
Safe current refers to the maximum current after electric shock. The safety current specified in China is 30 MA (50Hz). The safe current is related to factors such as electric shock time, current nature, current path, weight and health status.
7. Safe voltage concept:
Safe voltage refers to the voltage that does not cause direct death or disability. The safety extra low voltage stipulated in 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 the place about 20 meters away from the ground fault point.
9. Contact voltage and step voltage:
Contact voltage refers to the voltage to ground presented by people contacting the exposed conductive part of the equipment with grounding fault; Step voltage refers to the potential difference between two feet when a person walks near the grounding fault point.
10. Concepts of working grounding and protective grounding:
The grounding to ensure that the power system and equipment meet the requirements of normal operation is called working grounding.
The grounding to ensure personal safety and prevent indirect electric shock is called protective grounding.
For example, the neutral point grounding of transformer, the grounding of lightning arrester and lightning arrester are working grounding. The terminal grounding at the secondary side of the transformer and the equipment shell grounding are protective grounding.
11. Several protective grounding methods adopted in China at present:
There are TN system, TT system and it system.
Among them, TN system is divided into three protective grounding modes: TN-C, TN-S and tn-c-s.
12. Equipotential connection: equipotential connection can be divided into general equipotential connection and auxiliary equipotential connection.
The purpose of this method is to directly connect the conductive metal objects that people may contact with the PE line. Both internationally and in China, the general equipotential connection shall be implemented at the entrance of the power line, that is, all metal components and pipelines near the entrance of the power line shall be connected with PE line. Auxiliary equipotential bonding must also be carried out in particularly humid and electric shock dangerous places (such as bathrooms), that is, all metal components and pipes in the place must be connected with PE wires.
13. The first thing to do when someone gets an electric shock is to find a way to quickly disconnect the person from the power supply, and then give first aid in other ways.