What Is an Earthing System?

The grounding grid system is a grounding grid, which is a general term for a grounding body consisting of a plurality of metal grounding electrodes buried in a certain depth underground and a conductor connecting these grounding electrodes to each other to form a mesh structure. It is widely used in many industries such as electric power, construction, computers, industrial and mining enterprises, and communications, and plays a role of security protection and shielding. There are large and small grounding grids, some are very complicated and large, and some are only composed of one grounding pole, which are designed according to needs. In hydropower stations and substations, a special underground grounding body and the steel bars in the house are welded to form a grounding grid. All electrical equipment shells and transformer neutral points are connected to this grid. The size of the grounding resistance must meet national standards. Generally, the grounding resistance value of a hydropower station with a voltage level of 110 kV is 0.5 ohm, and the grounding resistance value of a hydropower station with a voltage level of 35 kV is 4 ohm.

1. Grounding conductor (pole)

A metal conductor buried in the ground and in direct contact with the ground is called a grounding body (pole). The grounding body is divided into a horizontal grounding body and a vertical grounding body.

2. natural earthing electrode

It can be used as a natural grounding body by using various metal members, metal well pipes, foundations of reinforced concrete buildings, metal pipes and equipment for direct contact with the earth for grounding.

3. grounding conductor

Under normal circumstances, the metal conductor used to connect the ground terminal of electrical equipment and towers with the ground body or the neutral wire is called a ground wire.

4, grounding connection

The sum of the grounding body and the ground wire is called a grounding device.

5, grounded

The ground wire is used to connect the power system or building electrical devices and facilities overvoltage protection devices with the grounding body, which is called grounding.

6, ground resistance

The sum of the resistance to ground and the resistance of the ground wire of the grounding body or natural grounding body becomes the grounding resistance of the grounding device. The value of the grounding resistance is equal to the ratio of the voltage of the grounding device to the ground and the current flowing into the ground through the grounding body.

Note: The above ground resistance refers to the power frequency ground resistance.

7.Power frequency ground resistance

The resistance is obtained by the power frequency current flowing into the ground through the grounding body, which is called power frequency grounding resistance.

8.zero line

The neutral line connected to the neutral point directly connected to the transformer or generator or the neutral line in the DC link is called the neutral line.

9. Protective ground (protective ground) protective ground

In a low-voltage power network where the neutral point is directly grounded, the enclosure of the electrical equipment is connected to the protective neutral wire, which is called protective earthing (protective grounding).

10.Concentrated grounding connection

Additional grounding devices, such as a vertical grounding body installed near the lightning rod, are laid to enhance the effect of lightning current dispersion and reduce ground potential.

11.Large-scale grounding connection

Grounding devices for substations with a voltage level of 110kV and above, grounding devices for thermal power plants and hydropower plants with an installed capacity of more than 200MW, or grounding devices with an equivalent planar area of more than 5000m2.

12.safe grounding

The metal casing of the electrical device, the structure of the power distribution device, and the line pole tower may be charged due to insulation damage. The grounding is provided to prevent it from endangering the safety of people and equipment.

The grounding grid consists of a vertical and horizontal grounding body with a grounding device that has the function of draining and equalizing.

When a single-phase ground fault occurs in a neutral point direct grounding system (including a system with a low impedance grounding), the ground short-circuit current is large, so this system is called a high-current grounding system. Use a system where the neutral point is not grounded or grounded via an arc suppression coil. When a ground fault occurs in a phase, this system is called a low-current grounding system because it cannot form a short circuit and the ground fault current is often much smaller than the load current.

The division standard of the high-current grounding system and the low-current grounding system is based on the ratio X0 / X1 of the zero-sequence reactance X0 to the positive-sequence reactance X1 of the system. China's regulations: X0 / X1. The system 4 5 is a large ground current system, X0 / X1. Systems> 4 to 5 are small ground current systems. Some countries (such as the United States and certain Western European countries) require X0 / X1. The system> 3.0 is a small ground current system ^[3] .