In the world of modern and safe electrical networks, measurement of Earth Resistance is an important process that helps in preventing electrical accidents.
What is Earth Resistance?
Earth resistance means the resisting power of the earth. It is an important geologic property that reflects the resistivity of the soil. It stops the electric current that flows to the ground. Earth resistance is measured in the unit Ohm (Ω) and is important for the path to ground. It is important in power generation projects, energy transmission and other geological studies.
There are various methods to find Earth Resistance, out of which two main methods are –
- fall,off,Potential method and
- earth tester
Fall-of-potential method
fall,off,Potential According to the method, special electrodes are used to measure earth resistance. In this process, an earth electrode is condensed into a thick rod, called a potential rod, at a distance of 10 meters. In addition, another rod is welded at a distance of 10 m from the potential rod, which is known as the current electrode. A voltmeter and an ammeter are connected between these rods. This process helps in measuring earth resistance and determines how much electrical resistance there is in the ground.
How is earth resistance determined by fall-of-potential method?
As shown in figure I, a voltmeter is connected in parallel between the current electrode and the potential electrode. And an ammeter is connected in series with the earth electrode. The other end of which is for supply.
With the help of a transformer, meter readings are taken by providing electric supply to the main earthing and current electrodes.
Readings are taken 2 to 3 times by changing the position of the potential electrode. And with the help of those readings the average resistance of that place is determined.
Generally earthing between 1.5 to 3 Ohm is considered good.
To find out earth resistance with earth tester
Earth tester is a meter which is used to measure earth resistance. This meter has Ohm symbols and has E, P, and C terminals for connections. The main earth electrode is connected to the E terminal, while the potential and current electrodes are connected to the P and C terminals. This meter measures the earth resistance when the handle is rotated by hand at the rated speed and displays it for suitable riding.
Method to find earth resistance with earth tester
Meaning to know the resistance. The main earth electrode has to be connected to the E terminal of the earth meter. A potential electrode is buried in the ground at a distance of 10 meters from the main earth electrode and its connection is made with the P terminal of the earth meter. At a distance of 10 meters from the potential electrode, a current electrode is buried in the ground and its connection is made to the C terminal of the earth meter.
The riding shown on the meter display when the handle of the earth tester rotates at the rated speed. That place means resistance.
If this resistance is less than 5 Ohm then the earthing done there is good. It is said so.
By using both these methods the process of measuring earth resistance becomes easy and safe. Through this, electrical engineers and technicians are able to ensure the safety and functionality of the power network, thereby reducing the possibility of accidents.
