SOLUTION

The ground of the substation yard is filled with crushed gravel stones. Generally, 20 to 25 mm baby gravel stones are used instead big size stones to facilitate the movement of persons and equipment in the substation yard. This is because of the following reasons concern to safety from shock:

1. It provides a high resistance layer or insulation between our feet and the ground. So that the fault currents flow into the ground but not along the ground.
2. To minimize step potential and touch potential voltages.
3. It avoids a pool of inflammable oil, etc. on the substation ground in case of any spilling of insulation oil from the equipment. This also avoids spreading free from one equipment to the other in the substation.
4. It restricts the entering of snakes and other reptiles as the surface would be inconvenient to crawl.
5. It avoids the growth of plants and weeds in the substation yard to some extent.
6. Oil leakage takes place during operation or when changing the oil in the transformer. This oil spillage can catch fire is dangerous to the switchyard operation. So Stones is provided to protect from  fire when oil spillage takes place.