In sandy and stony soils with high earth resistivity, in order to meet the requirements of low ground resistance, a grounding network composed of multiple grounding bodies connected in parallel is often used. But sometimes a lot of steel is used, and the grounding area is very large. It is often difficult to achieve the required ground resistance. At this time, the geodetic resistivity of the soil near the grounding body can be reduced, and the purpose of reducing the grounding resistance can also be achieved. How to use the ground resistance tester in harsh environments? It is recommended to try the following methods.
1. Use soil with low resistance coefficient (i.e., soil replacement method).
Clay, peat, black clay and sandy clay can be used instead of soils with high resistance coefficients, and coke and charcoal can also be used if necessary. The replacement range is within 1 to 2m around the grounding body and within 1/3 of the length of the ground electrode near the surface. After this treatment, the grounding resistance can be reduced to about 3/5 of the original.
2, Use of salt and other manual treatment methods
Salt, cinder, carbon dust, furnace ash, coke ash, etc. are added to the soil around the grounding body to improve the conductivity of the soil. Since table salt has a good effect on increasing the soil resistance coefficient, it is less affected by seasonal changes and the price is low.
3, the use of external introduction grounding
Especially in hilly areas, when the ground resistance value is small and it is difficult to reach in situ, if there is a water source or soil with a low resistivity nearby, it can be used to make ground electrodes or lay underwater grounding nets. A grounding wire, such as a flat steel strip, is then used as the external grounding. However, the grounding resistance tester needs to pay attention to the fact that the external grounding device should avoid the pedestrian channel to prevent the step voltage electric shock; When crossing the highway, the burial depth of the outer lead should be greater than or equal to 0.8m.
4. Conductive concrete
Carbon fibers are mixed into cement for use as ground electrodes. For example, about 100 kg of carbon fiber is mixed into 1 cubic meter of cement to make a hemispherical (1 meter diameter) ground electrode. After measurement, its power frequency grounding resistance (compared with ordinary concrete) can usually be reduced by about 30%. This method is often used for lightning protection and grounding devices. In order to further reduce the impact grounding resistance value, the needle grounding electrode can also be embedded in the conductive concrete at the same time, so that the discharge corona fluctuates continuously from the needle tip and the carbon fiber, and the grounding has a significant effect and reduces the impact grounding resistance value.
5. Chemical treatment of resistance reducing agent
Resistance reducing agents with toner and quicklime as the main raw materials do not contain dielectric matter, will not be lost due to groundwater, and can be used in the soil for a long time. As a result, long-term contamination-free, stable low ground resistance (about 1/2 lower than before treating soil with resistive agents) can be obtained. For hard rock slab belts, the method of adding or subtracting inhibitors to the buried wire is very effective, and the grounding resistance tester ground resistance can be reduced by about 40% compared with the buried wire alone. This method can achieve good results by sprinkling a powdered drag reducer or a long-acting drag reducer in a ditch that excavates and lays the ground line, and then backfills the old soil.
