Soil treatment for reducing earth resistance
It is quite hard to achieve the required reduction in ground resistance by adding more grid conductors or ground rods to the earth grid. A probable alternative is to effectively increase the diameter of the electrode by modifying the properties of the soil surrounding the electrode. The innermost part of the soil, which is closest to the electrode normally comprises the bulk of the electrode ground contact resistance to remote earth. This phenomenon of soil treatment for reducing earth resistance is often utilized to advantage and is discussed in brief as follows:
Table of Contents
CHEMICAL CHARGING
The use of magnesium, sodium chloride, and sulfates of copper, or calcium chloride, to boost the conductivity of the soil immediately surrounding an electrode is another soil treatment for reducing earth resistance. Magnesium sulfate is widely used for this purpose as it is a cost-effective solution. Common salt, being cheap and commands good conductance of electricity, also has very high corrosive properties, which can affect the electrode. Further, the salt treatments must be renewed periodically. These treatments tend to increase the effective size of the electrode by modifying the soil in the surroundings.
BENTONITE
Good use of bentonite, which is a naturally occurring clay containing the mineral montmorillonite, which was formed by volcanic action years ago, is mostly used in soil treatment for reducing earth resistance. It is mostly noncorrosive, stable, and has a resistivity of 2.5 Ω m at 300% moisture. Its low resistivity results mainly from an electrolytic process between water, Na2O (soda), K2O (potash), CaO (lime), MgO (magnesia), and other salts that ionize forming a strong electrolyte with pH ranging from 8 to 10.
This electrolyte will not gradually leach out, as it is part of the clay itself. When provided with a sufficient amount of water, it swells up to 13 times its dry volume and will adhere to nearly any surface it touches. Due to its hygroscopic properties, it acts as a drying agent drawing any moisture that is available from the surrounding environment. Bentonite needs water to obtain and maintain its beneficial characteristics. The initial moisture content is obtained at installation when the slurry is prepared. Once it is installed, bentonite relies on the presence of ground moisture to maintain its characteristics.
While engineering this soil treatment for reducing earth resistance it has to be noted that most soils have sufficient ground moisture so drying out is not a concern in most parts of the world. The hygroscopic nature of bentonite takes advantage of the available water to maintain its installed condition. When it is exposed to direct sunlight, it prioritizes to seal itself off, preventing the process of drying from penetrating deeper. It may not function well in a very dry environment, because it can shrink away from the electrode, resulting in an increase of the resistance.
CHEMICAL TYPE ELECTRODES
This soil treatment for reducing earth resistance utilizes copper tubes that are filled with salt. Holes drilled or cut in the tube allow the moisture to enter, which dissolves the salts, and allows the salt solution to leach into the ground. This type of electrode is installed in an augured hole and typically backfilled with soil treatment for reducing earth resistance.
GROUND ENHANCEMENT MATERIALS,
Some materials with a resistivity of less than 0.12 Ω m which is about 5% of the resistivity of bentonite, are typically placed around the rod in an augured hole or around grounding conductors in a trench, in either a dry form or premixed in a slurry for the purpose of soil treatment for reducing earth resistance. Most of these enhancement materials are permanent and will not leach any chemicals into the local ground. Other available ground enhancement materials are mixed with local soil in varying amounts and will slowly leach into the surrounding soil, resulting in low earth resistivity.
MOISTURE REFILL
It is seen that soil loses moisture in direct sunlight. Moisture is known to help in better conduction by discharging electricity from the electrode to the surroundings. The H2O molecules ionize the minerals present and become conductive. There is a strong correlation between soil resistivity with water as the best soil requires 4% water by weight to have effective grounding resistance while the poorest soil type requires 14% water.
Areas have moisture more than required and some have close to none. So it is advisable to engineer a proper irrigation system that can keep the soil moist for effective grounding. It may also be noted that too much water drainage can wash away the minerals leaving the ground to be recharged with minerals again.
