Ways to reduce ground resistance
Safety production is more important than Mount Tai. In addition to strengthening management, technical measures are also an important link. The direct and effective technical measure to ensure the safe operation of lines and equipment is to do a good job of grounding protection. According to the technical design and engineering construction management experience, the current methods mainly include the following:
1 Change the soil
This method replaces the original soil with high resistivity with low resistivity soil (such as clay, black soil and sandy clay, etc.), and the replacement range is within 0.5m around the grounding body and 1/3 of the grounding body . However, this method of borrowing and replacing soil consumes a lot of manpower and working hours.
2 Artificial soil treatment (chemical treatment of soil)
Add chemicals to the soil around the grounding body, such as table salt, charcoal, furnace ash, nitrogen fertilizer slag, calcium carbide slag, lime, etc., to improve the conductivity of the soil around the grounding body. The use of table salt has different effects on different soils. For example, when sandy clay is treated with table salt, the soil resistivity can be reduced by 1/3 to 1/2, and the sand resistivity can be reduced by 3/5 to 3/4. The resistivity of sand decreases by 7/9 to 7/8; for rocky soils, the conductivity can be increased by 70% after being impregnated with 1% salt solution. Although this method has low engineering cost and obvious effect, the soil will reduce the thermal stability of the grounding, accelerate the corrosion of the grounding body, and reduce the service life of the grounding body after manual treatment of the soil. Therefore, in general, it is recommended to be adopted only under extreme conditions.
3 Deep buried electrode
When the resistivity of soil or water in the ground is low, a deep buried ground electrode can be used to reduce the ground resistance. This method is most effective on sandy soils. According to relevant data, the soil resistivity at 3m depth is 100%, at 4m depth is 75%, at 5m depth is 60%, at 6m depth is 60%, at 6.5m depth is 50%, at 9m depth is 20%, this method can ignore the increased resistivity of soil freezing and drying, but the construction is difficult, the amount of earthwork is large, the cost is high, and the difficulty is even greater in rocky areas.
4 Multiple external grounding devices
This method can be used if there are well-conducted and non-frozen rivers and lakes near the grounding device. However, when designing and installing, the influence of the resistance of the grounding pole main line must be taken into consideration. Therefore, the length of the externally leading grounding pole should not exceed 100m.
5 Use grounding resistance reducing agent
After the resistance-reducing agent is placed around the ground electrode, it can play the role of increasing the size of the ground electrode and reducing the contact resistance with the surrounding ground medium, so that the ground resistance of the ground electrode can be reduced to a certain extent. When the resistance-reducing agent is used for small-area concentrated grounding and small-scale grounding grid, its resistance-reducing effect is more significant.
Drag reducing agent is a chemical drag reducing agent formulated from several substances, it is a strong electrolyte and moisture with good conductivity. These strong electrolytes and water are surrounded by reticulated colloids, and the spaces of the reticulated colloids are filled with partially hydrolyzed colloids, so that it will not be lost along with groundwater and rain, so it can maintain good conductivity for a long time. This is a relatively new and actively popularized method currently adopted.
6 Use water and water-reinforced concrete body as the flow medium
Make full use of metal structures in hydraulic structures (water wells, pools, etc.) and other concrete in contact with water as natural grounding bodies. You can choose some vertical and horizontal intersections among the many reinforced meshes bound in underwater reinforced concrete structures The spot is welded and connected to the grounding grid.
When using a hydraulic structure as a natural grounding body still fails to meet the requirements, or when using a hydraulic structure as a natural grounding body is difficult, it is preferred to lay an external (manual) grounding device in the nearest water (river water, pool water, etc.) (Underwater grounding grid), the grounding device should be laid in a place where the water flow rate is not large or in still water, and some large stones should be backfilled to fix it.
7 Take an elongated horizontal grounding body
Combined with the actual application of the project, after analysis, the results show that when the length of the horizontal grounding body increases, the influence of the inductance increases accordingly, thereby increasing the impact coefficient. When the grounding body reaches a certain length, then increase its length, impact grounding The resistance no longer drops. Generally speaking, the effective length of the horizontal grounding body should not be greater than. The effective length of the grounding body is determined according to the soil resistivity as shown in Table 1.
Table 1 Effective length of horizontal grounding body under different soil resistivities
Soil resistivity (Ωm) 500 1000 2000
Effective length of horizontal grounding body (m) 30 ～ 40 45 ～ 55 60 ～ 80
8 Take sewage introduction
In order to reduce the resistivity of the soil around the grounding body, sewage can be led to the buried grounding body. The grounding body is made of steel pipe, and a small hole with a diameter of 5 mm is drilled in the steel pipe every 20 cm to allow water to penetrate into the soil.
9 Take deep well grounding
When conditions permit, deep well grounding can also be used. Drill holes with drilling rigs (exploration holes can also be used), drive the grounding electrode of the steel pipe into the well hole, and inject mud into the steel pipe and the well.
When determining specific measures to reduce the grounding resistance in areas with high soil resistivity, a comprehensive and comprehensive analysis should be carried out based on the original local operating experience, climatic conditions, topographic features and the level of soil resistivity, etc. , Choose a reasonable method according to local conditions. In this way, it can not only ensure the normal operation of lines and equipment, but also avoid the occurrence of excessive investment in the grounding device project.
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