What does a good grounding of the power substation and switching station really mean ?

The object of an earthing system in a substation is to provide under and around the substation a surface that shall be at a uniform potential and near zero or absolute earth potential as possible.

The provision of such a surface of uniform potential under and around the substation ensure that no human being in the substation subject in shock of injury on the occurrence of a short circuit or development of other abnormal conditions in the equipment installed in the yard.