Lightning protection grounding safety basic knowledge

 1. There are two basic forms of lightning overvoltage:
One is: direct lightning - also known as direct lightning
The second is: lightning induction - also known as induction lightning
  2. The role of the lightning receptor:
The lightning receptor is a metal body that is used to receive direct lightning strikes. It must be connected to the grounding device via a grounding down conductor.
3. The function of the lightning rod:
The role of the lightning rod is actually the role of lightning, it is used to protect the direct lightning.
4. Types and functions of lightning arresters:
Commonly used arresters are valve type, exhaust type (tube type), zinc oxide and the like.
The arrester is used to protect the lightning overvoltage from entering the power distribution room or other buildings along the line to avoid jeopardizing the insulation of the protected object. Zinc oxide surge arresters are often used outside the power distribution room, and valve arresters are commonly used indoors.
5. Lightning protection measures commonly used in factory power distribution rooms:
The lightning protection device is a lightning arrester that uses lightning rods (or lightning protection lines, lightning protection belts, and lightning protection nets) to protect against lightning strikes.
6. The concept of safe current:
The safe current refers to the maximum current that is removed from the human body after an electric shock. China's prescribed safe current is 30 mA (50HZ). The safe current is related to the time of the electric shock, the nature of the current, the current path, and the weight and health status.
7. Safety voltage concept:
A safe voltage is a voltage that does not cause direct death or disability. The safety extra low voltage prescribed in China is 36 volts.
  8. The concept of the ground:
Electrical ground (or earth) refers to a place where the potential is zero; this area generally refers to a location approximately 20 meters away from the ground fault point.
  9. Contact voltage, step voltage:
The contact voltage refers to the voltage of the ground exposed by the exposed conductive part of the device in contact with the ground fault; the step voltage refers to the potential difference between the two feet when the person walks near the ground fault point.
10. The concept 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 ground.
In order to protect personal safety, the grounding caused by contact electricity is called protective grounding.
For example, the grounding of the neutral point of the transformer, the grounding of the lightning receptor and the arrester is the working ground. The secondary side terminal of the transformer is grounded, and the ground of the equipment case is grounded.
11. At present, several ways to protect the grounding used in China:
There are TN systems, TT systems, IT systems.
Among them, TN system is divided into three protection grounding methods: TN-C, TN-S, and TN-C-S.
12. Equipotential bonding: Equipotential bonding can be divided into total equipotential bonding and auxiliary equipotential bonding.
The purpose of this approach is to connect the electrically conductive metal objects that people may be exposed to directly to the PE line. Both internationally and in China, it is stipulated that the main equipotential connection should be implemented at the entrance of the power line, that is, all the metal components and pipes near the entrance of the power line are connected with the PE line. In places that are particularly humid and dangerous to electric shock (such as bathrooms), an auxiliary equipotential bonding must also be performed, that is, all metal components and pipes in the site are connected to the PE line.
13. The first thing I did when I found someone getting an electric shock was to find a way to get the electric shocker out of the power supply quickly and then take other forms of first aid. (Excerpt from "China Industrial Control Network")

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Aug.26, 2019