Decreasing the cost of ground grid installations under difficult environmental conditions

The purpose of a ground grid is to provide a means to carry and dissipate electrical currents into ground under normal and fault conditions. In some cases, especially in dry rock terrain, the soil resistivity can be very high, making it difficult and very expensive to install an acceptable ground grid. Usually a soil resistivity above 200 ohm-meter is considered high. This paper discusses and provides design calculations for a successful ground grid installation in a distribution substation located in one of the worst soil conditions encountered in the industry; a very rocky terrain where the resistivity is 1800 ohm-m. It is a practical application of the theories presented in ANSI/IEEE Std. 80-1986. The design application consists of bare copper combined with conventional and a new type of ground rod. The installation cost for this application was much less than the cost associated with that of a conventional installation