A. 3.3 to 11kv
B. 2.2 to 33 kv
C. 33 to 66kv
D. 66 to 132 kv
B. 2.2 to 33 kv
C. 33 to 66kv
D. 66 to 132 kv
Answer: A. B. 2.2 to 33 kv
Explanation:
What is Resistance Earthing?
- The resistance offered by the earth electrode to the flow of current into the ground is known as the earth resistance or resistance to earth.
- The earth resistance mainly implies the resistance between the electrode and the point of zero potential. Numerically, it is equal to the ratio of the potential of the earth electrode to the current dissipated by it.
- The resistance between the earthing plate and the ground is measured by the potential fall method.
- In order to limit the magnitude of earth fault current, it is a common practice to connect the neutral point of a 3-phase system to earth through a resistor. This is called resistance grounding.
Advantages:
The following are the advantages of resistance earthing:
- The earth fault current is small due to the presence of earthing resistance. Therefore, interference with communication circuits is reduced.
- It improves the stability of the system.
Disadvantages:
- The following are the disadvantages of resistance grounding :
- Since the system neutral is displaced during earth faults, the equipment has to be insulated for higher voltages.
- This system is costlier than the solidly grounded system.
- A large amount of energy is produced in the earthing resistance during earth faults. Sometimes it becomes difficult to dissipate this energy to the atmosphere.
Applications:
It is used on a system operating at voltages between 2.2 kV and 33 kV with power source capacity of more than 5000 kVA.