Switchyard grounding mats in rocky soil

GROUNDING OF high-voltage stations usually is accomplished by a number of driven ground rods. However, when rocky ground makes this impractical, other methods must be used such as burying a number of conductors in a criss-cross fashion at a depth of from 1 to 2 feet parallel to the surface of the earth without using any driven rods. This not only effectively grounds the electric system, but has the added advantage of controlling the voltage gradients at the surface of the earth during faults. A measure of the effectiveness of a grounding grid is given by the resistance that current encounters in flowing from the buried grid conductors into ground. The allowable value of the resistance to ground will depend upon the single line-to-ground fault current at the switchyard concerned. Various design factors of the grounding grid influence its resistance to ground.