For reducing tower footing resistance it is better to use
Right Answer is:
Ground rod and counterpoise only
For reducing tower footing resistance it is better to use ground rod and counterpoise only.
Tower Footing Resistance
Tower footing resistance (Rt) is the resistance offered by the metal parts of the tower and the ground resistance and It is important for the protection against Surge Voltages.
Tower footing resistance depends on
1) Type of electrode configuration employed
2) Soil resistivity
3) Electrode shapes (Hemisphere, vertical driven rod, and Buried horizontal wires)
Methods for tower grounding are:
Buried Conductor: One or more conductors are connected to tower legs and buried in backfilled tower foundation. It is used when soil resistivity is low
Counterpoise Wire: A wire/ Strip of the length of 50 m is buried horizontally at depth of 0.5 m below ground. This wire is connected to tower legs. It is used when earth resistance is very high and soil conductivity is mostly confined to the upper layer
Ground rod: Pipe/Rod of 3 to 4 m is driven into the ground near the tower and the top of the rod is connected to the tower by a suitable wire/strip. It is used where ground conductivity increases with depth
Treated Earth Pits: Pipe/Rod of 3 to 4 m are buried in treated earth pits and the top of the rod is connected to the tower by a suitable wire/strip. It is used in very high resistivity near the tower.
Since the tower footing resistance depends upon the soil resistivity and critical breakdown gradient of the soil hence chemical treatment can be used this method requires regular checking of soil conditions at each and every tower which are several miles apart hence it is very much time-consuming. Therefore we use Ground-Rod and counterpoise.