By incorporating bentonite into the soil, the resistivity of the soil and the ground resistance of the electrodes are both decreased. Bentonite is a clay that is created by the activity of volcanoes. It has fine grains and high plasticity. This substance has the potential to serve as a substitute for soil and as a filler material for electrical grounding in areas that have a high resistance. 

Montmorillonite has been activated with sodium. Bentonite clay, which is conductive. Bentonite continues to maintain its qualities throughout time, in addition to being chemically hydrated and naturally stable.

It is possible for bentonite to expand to many times its dry volume as a result of its ability to absorb moisture from the soil around it. In order to reduce the contact resistance and artificially increase the diameter of the grounding rods and cables that have been put in trenches, it adheres to the surface of the grounding rods and cables.

How Does Bentonite React?

The following are some of the significant observations with regard to the reaction of Bentonite:

  • When there is water present in bentonite, the resistivity of the material changes and the electrical currents pass through the bentonite because of the water contained inside the pores. 
  • The value of resistivity is lower in the liquid state compared to the plastic or solid state, and it is around 250 Ω∙cm when the moisture content is 300% when the liquid state is present. 
  • Bentonite compound has a moisture retention mechanism that protects against corrosion. This is in addition to the fact that it lowers the resistance of rods and cables to grounding.

Factors Affecting the Performance of Bentonite

The quantity of rainfall, the moisture content of the soil, and the temperature at the location all have a significant impact on the performance of bentonite. Hot weather causes the soil to dry up, which results in the bentonite not functioning as well as it could. It is possible for it to get detached from the electrodes, which would increase the resistance to the ground. 

The ground improvement material (GEM) known as bentonite is extensively used and readily accessible inside the market. Because of its capacity to take in moisture, it is the most effective alternative for a good grounding system in high-resistance soil, particularly rocky soil. 

For grounding, there are two components that make up the lightning protection system: the ground electrode and the ground medium. In order to design an effective grounding system, it is recommended to make use of the best ground electrode. This electrode has a high conductivity, which allows the surge current to be grounded in a shorter amount of time. 

In addition to this, the electrode must be able to endure the corrosion process that occurs in the soil in order for it to have a longer lifespan. Additionally, the electrode must be mechanically robust in order to withstand the recurrent fault and surge current.

Bentonite’s Absorption Rates to Consider

At a density of six times its dry volume, the earthing compound is highly thick and in a pasty clay state that may hold form and stick to surfaces. Bentonite is capable of absorbing up to five times its weight in water, and the clay that retains moisture will expand to thirteen times its dry volume. 

The clay compound known as bentonite is non-corrosive, naturally stable, and will maintain its qualities throughout the course of time. Bentonite hydrates chemically, which means that it retains water inside its structure.

Following the completion of the duct filling process, the earthing compound mixture should be injected into the cable duct while ensuring that air is excluded. Once the duct filling process is complete, all of the ducts should be sealed to prevent any leakage or escape of the Bentonite. Granular or powdered forms of the earthing compound are both available for purchase, and the expansion ratio of the compound when it is combined with water is typically 2:1.

Granular Bentonite is the preferred option for filling trenches because the substance can be mixed in the cable trench. Powder Bentonite, on the other hand, is suitable for pouring into boreholes to ensure that the mixture is of a thin enough consistency to reach the bottom of the hole. Granular Bentonite is easier to handle, process, and use than powder-type compounds.

Advantages of Bentonite Earthing Compounds

The following are the advantages of Bentonite when used for earthing enhancement:

  • Reduces Resistance

Bentonite is used to reduce the resistance to earth by providing ground augmentation. This is accomplished by successfully lowering the resistance between the soil and earth electrodes (such as copper earth rods or earth mats) by the retention of moisture contained within the soil. 

  • Positive Association

There is a positive association between the electrical conductivity of the earthing compound and the local climatic circumstances, notably the average rainfall levels. This intrinsic tendency to absorb and retain rainwater improves the property of the earthing compound. 

  • Cost-efficient material

Bentonite compound is a cost-efficient material for backfilling earth electrodes and improving performance in situations where it is physically impossible to drive the earth rods deeper and where challenging ground conditions exist, such as rock, granite, and other similar conditions. In general, the compound has a resistivity level of three ohms.m.

  • Lowers Ground resistance

Chemical treatment or backfilling of the soil in close proximity to the location of an underground earthing electrode is a well-established and time-honored method of lowering ground resistance for substation earthing on high-resistivity ground. This type of soil backfilling for electrical grounding improvements is commonly used on low-voltage, medium-voltage, and high-voltage applications.

Wrapping Up!

There is no precise mixing ratio, and this varies according to local electrical utility and DNO engineering standards and preferences related to ground conditions and resistivity readings of the earthing compound. The plasticity and viscosity of the earthing compound ensure that the utility or civil engineering contractor will have an easy time installing and using the earthing compound. It is necessary to completely and violently mix the compound with water in order to obtain an equal consistency in the form of a slurry, which is suitable for dumping into the cable trench, borehole, or job site. 

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