An earthing grid is made up of a number of rods connected together by copper conductors. Earthing grid is also known as the earthing mat. It looks like a mesh of conductors. The purpose of earthing grid is to reduce the overall grounding resistance. It also helps in limiting the potential gradient. It is a part of the electrical earthing system.
In the case of faulty conditions, the fault current dissipates into the ground along a path of low impedance provided by earthing grid.
Importance of Earthing grid
Since the human body is able to carry electric current easily, potential differences in touch voltage and step voltage, as well as their combination, present a life-threatening danger to the body. The installation of an earthing grid is a simple and effective method of eliminating these hazards.
Important factors to consider when designing an earthing grid
When an earthing system fails, it may cause disastrous consequences for the equipment, as well as the person operating the equipment. The proper design of earthing systems is therefore essential for ensuring the safety of electrical systems. The following factors must be taken into consideration when designing an earthing grid:
1. In the event of a fault, a voltage may appear between the ground surface and the buried conductor. This voltage should not pose a danger to a person whose hands may come into contact with a non-current-carrying conducting surface of the plant at the time of the fault.
2. To operate the protective relays, there must be sufficient sustained fault current flowing into the earthing grid to operate the relays, i.e., the grounding resistance must be low enough to permit fault current to flow.
3. It is important that the resistance of the mat is not of such a magnitude that it would permit the flow of fatal currents in the live body.
4. When designing the earthing grid, it should be designed so that the step voltage is less than the permissible value. The permissible value varies according to the soil’s resistivity and the time required to isolate the faulty plant from the live system.
Step potential, touch potential, and ground potential rise play an important role in earthing grid design in order to ensure complete electrical safety when faults occur. It is important to consider soil resistivity when designing earthing grids to achieve the desired values. The nature of soil differs with respect to location; therefore, soil resistivity analysis is extremely important.
High soil resistivity values, limited availability of area, and a lack of appropriate tools for designing and soil resistivity analysis are the main challenges we encounter. A soil can consist of multiple layers both horizontally and vertically. As a result, it is important to know the number of layers in the soil before designing the multi-layer earthing grid. This allows us to design the earthing grid based on the site conditions in real-time.
It will be necessary to use some computer-assisted software available in the world, such as CDEGS software, in order to accomplish this task. With the help of this software, we are able to optimize the design of the project as well as validate the design according to site data collected in real-time.