Correct Answer : Option (D) :   All of the above

Explanation : Stones or crushed rock are provided in the substation to provide an extra layer of high resistance between the soil and a person walking or standing over there. It provides a safety layer that reduces the step and touch voltages that occur during ground faults, which can happen both inside and outside the substation.

All substations are designed with a ground grid. Copper conductors are arranged in a grid pattern and laid in trenches dug into and buried in the soil when the substation is constructed. If the crushed rock were not used, more copper would be needed in the ground grid to achieve tolerable step and touch voltages during ground faults.