Electricity is the most basic need for development. But that same electricity can produce destruction if not used in an appropriate way. That’s why safe manners should be adopted for Electricity utilization.
In power system, Earthing is the first sign of safety ! Safety for both- Humans & Machines. Earthing provides safe path to undefined currents; in situations like over voltage, Insulation breakdown & Lightning conditions.
A GIF below shows the working of Earthing ! A antenna above the house connected with Earthing . When lightning fall on the antenna, high current flows towards the Earthing .
EARTHING
Earthing is a type of sink which signifies zero potential. In Earthing, an electrical conductor is buried deep down in the earth. It is in contact with soil where an additive been poured to make the earth resistivity lower.
Another side of the buried conductor is above the ground. It is connected to the system either through a cable or a flat conductor.
Earthing ensures zero potential which provides an easy path for the fault current. Earthing effectiveness been calculated with its resistance value which is having the units ‘ohm‘.
- An ideal Earthing is having a resistance of zero ohm.
- But in Practical situation this value is difficult to maintained.
- And there is no fixed standard for it.
- According to IEEE(institute of Electrical & Electronics Engineers) Resistance value should be down below of 5 ohm.
- The Earthing resistance is all depend upon the system’s need where it is going to be connect. Such some sensitive & substation requires an Earthing up to 0.5 ohm.
EARTH TESTING
Metals, moisture, and minerals in the soil cause earthing electrodes or joints to deteriorate. As a result, the earth’s resistance increases with time.
It is important to verify the Earthing at least once in a year. Record should also be maintained so that resistance variation should be monitored.
In Today’s era, There are multiple gadgets which are available for Earthing testing. Multiples gadgets have multiple ways for Earthing testing.
In this post, Fall of potential method is going to be discussed next. This fall of potential method is utilized to determines the earthing resistance.
FALL OF POTENTIAL METHOD FOR EARTHING TESTING
There are multiple ways of Earthing testing with multiple digital devices. In this post, the most basic and oldest method of Earthing testing will be discussed. That is ‘fall of potential method‘.
The idea behind this method involves monitoring a resistance value of Earthing including the resistance of near by soil. This value is measured from a earth terminal to up to a minimum straight distance of 20 meters. That resistance value is been considered as its resistance value.
For better discussion about this testing, Digital Earth Resistance tester by WACO is discussed next.
This device contains four terminals E1,P1,P2,E2. Terminals E1 & E2 are current terminals While P1 & P2 are voltage terminals which detects potential difference.
This device has 2 range selections 10Ω & 1000Ω. To start this test, A test button is provided.
In this method, 2 Earth spikes are used Which are buried in soil with equal distances from main earth electrode. Both the spikes are aligned in the same line. This alignment forms a line of three.
The Main Earthing electrode is placed first. The 1st spike is buried with a least distance of 20 meters from the main earthing electrode. The 2nd spike is buried at a distance of 20 meters from the 1st spike. As shown in an image below:
CONNECTIONS & WORKING OF FALL OF POTENTIAL METHOD OF EARTH TESTING
Main Earthing under the test; is connected to E1 & P1 terminals of the device. First spike is connected to P2 While second spike is connected to E2 as shown in an diagram below:
A Test button is pressed. The main earth electrode passes a known current through an outer spike. The spike is situated at a least distance of 40 meters. A voltage is been measured in between Main earth electrode & inner spike. At that same time, Ohm law is utilized to finding out the resistance; R=V/I
A GIF below totally explained the working of “Fall of potential method”.
WHY DO ITS BEEN NAMED SO, FALL OF POTENTIAL ??
Normally, for resistance calculation, A known voltage difference is applied across the test specimen. Then a unknown current is been measured. According to ohm’s law; R=V/I ; Resistance value is calculated.
But in earth testing method, A known current is applied across the outer circuit. While a unknown ‘voltage fall across‘ the inner circuit. Which is been recorded that’s why this method is known as fall of potential method.
WHY THERE ARE TWO STAKES ?
Let suppose there are one stake. Working Earth resistance remains near around 1Ω. This means; the Earth Electrode and only a single stake are existing in a continuous state. We can also say they are in a short circuit state.
1st condition, Voltage can not be applied across because voltage can not be applied across short circuit.
2nd condition, if a known current is applied, Then how can a voltage been measured across the short circuit ?
In the fall of potential method, a known current is applied across the outer circuit. Meanwhile, a voltage is measured across the inner circuit. That’s why two stakes are used in the fall of potential method.
SUM UP
- In power system, Earthing is the first sign of safety ! Safety for both- Humans & Machines.
- Earthing provides safe path to undefined currents; in situations like over voltage, Insulation breakdown & Lightning.
- Earthing is a type of sink which shows zero potential. In Earthing , an electrical conductor is buried deep down in earth. It is in contact with soil where an additive is poured to make the earth resistivity lower. Another sides of buried conductor; above the ground; is been connected to the setup either through cable or flat conductor.
- Earthing effectiveness been calculated with its resistance value which is having the units ‘ohm‘.
- An ideal Earth is having a resistance of zero ohm. But in Practical situation this value is difficult to achieve
- According to IEEE(institute of Electrical & Electronics Engineers) resistance value should be down below of 5 ohm.
- The Earthing resistance is all depend upon the network’s need where it is going to be connect.
- Metals, moisture, and minerals in the soil cause the deterioration of the Earthing electrode or joints. As a result, earthing resistance increases with time. It is important to verify the Earthing at least once in a year.
- Fall of potential is one of the method for Earthing resistance measurement.
- In fall of potential method, 2 spikes are aligned linearly at a equal distance from main earthing electrode.
- A known current flows between the earthing electrode and the outer stake. A voltage is measured between the Earthing electrode and the inner stake. At last, Through ohm’s law, Earthing resistance is calculated.