Proper grounding system will assure the safety of people and protection of equipments at faults. In large electrical system like power house or a substation has a grounding mesh instead of a single conductor.
The substation earth provides the connection to earth at zero potential. But at fault conditions potential of the grounding mesh rises due to grounding resistance. This produces potential gradients within and around the substation ground area. This leads following potential differences applied at people.
Step Potential- Potential difference between a person’s feet 1meter apart.
Touch Potential- potential difference between a person’s outstretched hand touching a grounded structure and his feet.
Mesh potential – Potential difference between the center of the grounding mesh and a grounded structure.
Transferred Potential – Potential difference between a grounded structure extended far away from the mesh and a point of the earth.