To Provide low impedance path to fault currents to ensure prompt and consistent Cooperation of protective devices during ground faults.
To keep the maximum voltage gradient along the surface inside and around the substation within safe limits during ground faults.
To protect the life and property from over voltage.
To stabilize circuit potential with respect to ground and limit the overall potential rise.
The Requirements of Good Earthing
Sufficient / higher surface area of conductor in contact with soil.
Soil should not be sandy, because current dissipation is better in damp soil as compared to sandy soil whish offers greater resistance.
The presence of earthing ingredients, which are responsible for enhancing the earth resistivity and for keeping the resistance down.
The adhesion property between conductor and soil should be good in order to have positive contact between conductor & soil.(The contact between dissimilar materials called as adhesion property)
The conductor if possible should be self sufficient in absorbing the current during leakage of current to the ground.
Since plate/strip dissipates the current directly to soil hence the process called as "Single Stage Current Dissipation process". If possible by any means if process can be made as "Multi Stage Current Dissipation" then it will be fast enough to dissipate current to the ground.
Earthing Traditional
In plate/strip earthing, since it has only two faces dissipates the current only in two directions i.e. "Bi-directional Current Dissipation" process.
Since earth connectivity with the plate/conductor is equal to its height (which is normally 2' to 3') hence ground available will be only "Two directional and limited to height of plate only". Hence sometimes in times of high surges /leakage current from the machine the residual charge is built up in the machine circuit thus may damaging the circuit /accessories sometimes.
The tendency of current is normally dissipates towards the corners. Thus creating potential difference between corners & center and making the area as "Unequipotential Source" of current dissipation thus resistance becomes inconsistent.
Chemical Earthing with CPT(Concentric Pipe technology)
Since the tendency of circular area is to dissipate the current in all direction, hence circular conductor becomes source of multidirectional i.e. 360 degree angle for dissipation.
Because of Concentric Pipe Technology the inner pipe also dissipates current in chemical and soil (thru. Other pipe) along with outer, thus making the electrode /conductor source of current dissipation.
Since there are no sharp edges or corners in the electrode the conductor behave as "Equipotential Source of Current Dissipation" thus making the electrode as source of consistent resistance.
The normal length of electrode is around 2 meter and along with its multidirectional nature of current dissipation, it makes the area for dissipation is almost 4 to 5 times than provided by plate/strip Earthing.
The Electrode Earthing installed with infill Chemical Compound making it virtually maintenance free because there is no need to put the mixture of water/salt. But if soil conditions are extremely dry then water should be poured at least once in three months, so that chemical able to retain moisture otherwise dampness is created around the electrode by hygroscopic nature of chemical.
Low impedance path provided by the system guide fault currents to ensure prompt and consistent Cooperation of protective devices during ground faults.
Keeps the maximum voltage gradient along the surface inside and around the object within safe limits during ground faults
Stabilize circuit potential with respect to ground and limit the overall potential rise.
