- To ensure safety to personnel in substations against electrical shocks.
- To provide the ground connection for connecting the neutrals of stat connected transformer winding to earth ( neutral earthing ).
- To discharge the over voltages from overhead ground wires or the lightning masts to earth. To provide ground path for surge arresters.
- To provide a path for discharging the charge between phase and ground by means of earthing switches.
- To provide earth connections to structures and other non-current carrying metallic objects in the sub-station (equipment earthing).
|Earth Mat in 110kV side of a 220/110 kV Substation|
Earth Resistance Value
If earth fault current is I, earth resistance is R, the voltage rise under short circuit condition would be V= IR.
The permissible potential rise and the maximum possible earth fault current set a limit on the maximum value of earth resistance.
To achieve earth resistance within specified limits, enough number of earth spikes and sufficient surface area of the earth grid and closer ground mesh rods are necessary.
The touch potential and earth potential in the switchyard under any earth fault condition should be within safe limits.