If you get a chance to visit any substation or Switchyard, you will notice that the surface of the Switchyard is fully covered with small size Gravels.

The use of gravels on the surface has the following things to do:

  • Although Substation / Switchyard grounding is very low in the range of 0.5 to 5 Ohm to provide low resistance path, the entire ground is filled with gravels to provide a high resistance layer so that it can act as an insulation between our foot and the ground.
  • The layers of Gravels on the substation/ Switchyard surface provide high resistance so that the fault currents flow into the ground but not along the ground. Thus, Step Potential and Touch Potential are reduced.
  • The layers of Gravels avoid pool of inflammable oil on the surface of Switchyard in case of any spilling of insulation oil from the equipment. This avoids spreading of fire from one equipment to the other in the Switchyard.
  • The layers of Gravels avoid growth of plants and weeds in the substation yard to some extent.
  • Generally 20 to 25mm gravel stones are used instead big size stones to facilitate movement of persons and equipment in the substation yard.
  • The most important function of Gravel is to reduce the step size of the person and hence the Step Potential.

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