Classification of grounding systems and the specific situation of each type!

The grounding system consists of a plurality of metal grounding electrodes buried at a certain depth underground and a grounding body that connects these grounding electrodes to form a network structure by conductors.

It is widely used in many industries such as electric power, construction, computers, industrial and mining enterprises, communications, etc., and plays a role in safety protection and shielding. Grounding grids can be large and small, some are very complex and large, and some are composed of only one grounding electrode, which is designed according to needs.

In hydropower stations and substations, a grounding network is welded into a grounding grid by a special underground grounding body and steel bars in the house, and all electrical equipment shells and transformers are neutrally connected to this network, and the size of the grounding resistance should meet the national standards. Generally, the grounding resistance value of hydropower stations with 110 kV voltage level is ohms, and the grounding resistance value of hydropower stations with 35 kV voltage level is 4 ohms.

Provisions for the grounding system:

When a single-phase ground fault occurs in a neutral direct grounding system (including a system grounded with a small impedance), the ground short-circuit current is very large, so this kind of system is called a high-current grounding system. Adopt a system that is neutral and not grounded or grounded through an arc suppression coil. When a grounding fault occurs in a certain phase, because it cannot form a short-circuit loop, the grounding fault current is often much smaller than the load current, so this kind of system is called a low-current grounding system.

The classification standard of high-current grounding system and low-current grounding system is based on the ratio of zero sequence reactance x0 to positive sequence reactance x1 x0 x1 of the system. Our country stipulates: where x0 x1.

The system of 4 5 belongs to the high ground current system, x0 x1. > 4 5 systems are small ground current systems.

The above content reference:Encyclopedia - Grounding system.

It consists of a grounding body and a grounding wire. A metal conductor that is in direct contact with the soil is called a grounding body. The metal conductor that the electrical equipment needs to be grounded to connect to the grounding body is called the grounding wire.

Grounding bodies can be divided into two categories: natural grounding bodies and artificial grounding bodies. Natural grounding bodies include: water pipes and other metal pipes buried in the ground (except for pipelines for liquid fuels and flammable and explosive gases); metal well pipes; Metal structures in which buildings and structures come into contact with the earth or underwater; reinforced concrete foundations of buildings, etc.

The artificial grounding body can be vertically embedded angle steel, round steel or steel pipe, as well as horizontally embedded round steel, flat steel, etc. When the soil is strongly corrosive, the surface of the grounding body should be tinned or hot-dip galvanized, and the cross-section should be appropriately increased. The horizontal grounding body can generally be used with round steel with a diameter of 8 10 mm.

The length of the steel pipe of the vertical ground body is generally 2 3 meters, the outer diameter of the steel pipe is 35 50 mm, and the angle steel size is generally 40 4 or 50 50 4 mm. The top end of the artificial grounding body should be buried meters below the surface of the ground. Below this depth, the soil conductivity changes little due to the influence of the season, the grounding resistance is stable, and it is not easy to be damaged by external forces.

There are horizontal grounding bodies and vertical grounding bodies, generally with angle steel flat steel, special copper-clad steel, ion grounding electrodes and other technical problems can be communicated 308133286

Grounding protection system: IT system, TT system, TN system Low-voltage distribution grounding system is divided into three forms: IT system, TT system and TN system.

The neutral operation mode of China's power system mainly includes: the neutral point is not grounded, the neutral point is grounded through the arc suppression coil, the neutral point is directly grounded, and the neutral point is grounded by resistance or reactance.

Among them, the neutral point is grounded by impedance, and is divided into high-impedance grounding and low-impedance grounding according to the size of the grounding current. At present, in China, 330kV and 500kV ultra-pants simple roll high-voltage power grids adopt neutral direct grounding mode, and 110-220kV power network also adopts neutral point direct grounding mode.

However, in some areas where lightning accidents are more serious and the 110kV in some large grids is grounded, the neutral point is grounded through the arc suppression coil to improve the reliability of power supply. 20-60kV power grid, generally using neutral point arc suppression coil grounding mode, when the grounding current is less than 10A, also use the judgment not grounding mode, and in the cable power supply of the urban power grid.

When the grounding current is greater than 30A, the grounding method through the arc suppression coil should be used, and the cable line used in the city network is used to use the cable line is.

Sometimes it is only when the grounding method with a small resistance is used. The power network below 1000V can be grounded at the neutral point or not grounded, and there is only a three-phase four-wire power network with V. To ensure the safety of personnel. Its neutral point must be directly grounded.

Crisis of China's power system:

In addition to reducing the income of employees, the State Grid Corporation of China also clearly requires that "the salary income of the members of the leadership team of each unit shall be included in the management of the headquarters of the State Grid Corporation, and the headquarters shall formulate unified measures for the management of the remuneration of the person in charge of the enterprise, so as to prevent the person in charge of the enterprise from setting his own salary." ”

As for the personnel not involved in the system, especially the person in charge of the unit, units at all levels have begun to submit "salary plans" to the higher levels. Although the specific standards for wage reduction vary from place to place, they are basically implemented in accordance with the standard that "the growth of the total wage of enterprises is lower than the growth of economic efficiency, and the growth of the average income of workers is lower than the growth of labor productivity."

The grounding system is divided into three types: IT, TT and TN, among which the TN system is divided into TN-S, TN-C-S and TN-C.

The meaning of the three literal symbols of the grounding system: TN, TT and IT: The first letter describes the relationship between the live conductor of the power supply and the earth, that is, how to deal with the grounding of the system

t: A point of power (usually a point on a neutral line) that is directly connected to the earth (t is the first letter of the French word "terre").

i: The power supply is isolated from earth or a point of the power supply is subjected to high impedance (e.g. 1000; ) is connected to the earth (i is the first letter of the French word "isolation").

The second letter describes the relationship between the exposed conductive part of the electrical installation and the earth, i.e. how to deal with protective grounding.

T: The exposed conductive part is directly connected to the ground, and it has no connection with the grounding of the power supply.

n: The exposed conductive part is grounded by a connection to the neutral point of the grounded power supply (n is the first letter of the French word neutre for "neutral point").

The IEC standard divides TN systems into three types according to different combinations of N lines and PE lines:

TN-C system: The N-line and the PE line are integrated throughout the system (C is the first letter of the French word "one"). Note, here.

The whole system is calculated from the outlet of the power switchboard. The same applies hereinafter.

TN-S system: The N-line and the PE line are separated throughout the system (S is the first letter of the French word "separate").

TN-C-S system: In the whole system, usually only the N line and the PE line are integrated before the power supply inlet point of the low-voltage electrical installation, and the power supply is separated after the inlet point.

for two wires. Usually we divide grounding into:

1. Work grounding.

2. System grounding.

3. Lightning protection and grounding.

4. Protective grounding.

According to the various protection methods and terminology concepts stipulated by the IEC, the low-voltage power distribution system is divided into three categories according to the different grounding methods, namely TT, TN and IT systems.

The TT method refers to the protection system that directly grounds the metal shell of the electrical equipment, which is called the protective grounding system, also known as the TT system.

The TN power supply system is a protection system that connects the metal shell of the electrical equipment with the working neutral line, which is called the zero connection protection system, which is represented by TN.

The IT mode power supply system indicates that there is no working grounding on the power supply side, or it has been grounded with high impedance, indicating that the electrical equipment on the load side is grounded for protection, which is represented by IT.

According to the use, it can be divided into three types, namely protective grounding, working grounding, and lightning protection grounding.

Answers]: a, c, d

According to Article 1 of the Code for Grounding Design of AC Electrical Installations (GB T 50065-2011), power systems, devices or equipment should be grounded according to regulations. The grounding device should make full use of the natural grounding electrode, but the thermal stability of the natural grounding electrode should be verified. Grounding can be divided into system grounding, protective grounding, lightning protection grounding and anti-shed crying electrostatic grounding according to the function.

Poor silver answers]: a, b, c

The grounding system includes the indoor part, the outdoor part of the room and the underground grounding network of the building. The working grounding of the equipment and the grounding of the rack protection are both indoors, not the outdoor part.

The function of system grounding is to provide a reference potential to the distribution system and make the distribution system normal and Anchai Feng operation D, a 220 380V distribution system after the neutral point grounding, its ground potential is roughly "clamped" on the voltage of 220V, so as to reduce the requirements of the system for ground insulation. When a lightning strike occurs, the distribution line induces a large amount of charge, and the system grounding can discharge the lightning charge to the ground, reduce the lightning transient impulse overvoltage on the line, and avoid the insulation of the line and equipment from being damaged by breakdown. Another example is the overhead line of high and low voltage co-pole, if the high-voltage line falls on the low-voltage line, it will cause danger to the low-voltage line and equipment.

After the system is grounded, it can form a high-voltage line fault current through the earth to return to the high-voltage power supply, so that the high-voltage side relay protection detects the fault current and acts, so as to eliminate this danger. When a grounding fault occurs in a low-voltage distribution line, the system grounding also provides a path for the fault current to return to the power supply through the ground, so that the protective appliances on the low-voltage line can act. If the system is not grounded, when a ground fault occurs in one phase of the system, the voltage of the other two opposing ground will be as high as 380V.

Because there is no conductor path to return the power supply, the fault current is only the phasor sum of the capacitance current of the two non-fault phase lines to the ground, and its value is very small, the usual overcurrent protection electrical appliances can not act, Sui Jingsheng This fault overvoltage will continue to exist, if the human body touches the non-fault phase line, the contact voltage will be 380V, and the risk of death by electric shock is very great. In addition, electrical equipment and circuits will continue to withstand 380V overvoltage to ground, which is also detrimental to its insulation safety. There are also power distribution systems that do not do system grounding, which is for special needs, and it needs to also have power distribution systems that do not do system grounding, which is for special needs, and it needs to be supplemented with some safety measures.