Factors Affecting Earth Resistance
Q. Explain factors affecting earth resistance.
Earth Resistance or Resistance to Earth :
The resistance offered by the earth electrode to the flow of current into the ground is known as resistance to earth. The term Resistance to Earth of Earth Resistance does not imply the contact resistance between the earthing electrode and soil (which is insignificant) but mainly the resistance of soil “between the electrode and the point of zero potential. Numerically, it is equal to the ratio of the potential of earth electrode w.r.t. the remote point to the current dissipated by it.
Mathematically, earth resistance is given as V/I where, V is the measured voltage between the electrode and the voltage spike and I is the injected current during the earth resistance measurement through the electrode.
As a general rule, lower the value of earth resistance better it is. But even then following values of earth resistance [Max. permissible] values will give satisfactory results.
Large power stations : 0.5 Ω
Major power stations : 1.0 Ω
Small substations : 2.0 Ω
In all other cases : 8.0 Ω
