1. to maintain safe voltages across the station area during high voltage system transients,

2. to provide a low impedance ground fault current return path,

3. to maintain safe voltages within station structures during electrical transients,

4. to minimize the noise interference in instrumentation systems, and

5. to minimize the effects of lightening surges on equipment and structures.

The electrical resistivity method is a non-destructive method for subsurface investigation. In this method, a known amount of current is injected into the earth and the resulting potential difference is measured. The method is based on the fact that different subsurface materials offer different resistance to the passage of an electrical current. Thus, by the determination of vertical and lateral variations in this resistance the subsurface deposits can be delineated.

The most important parameters in designing the station grounding system is the resistivity of soil in the station area. There are two resistivity values required for the design of a grounding system; one is the resistivity of large volumes of soil. To obtain these values, an extensive soil resistivity survey has been conducted in the station area. The resistivity measurements were conducted by Schlumberger and Wenner methods for fifty points in two directions i. e. North-South and East West at the proposed site situated in Seismic zone V. The interpretation of field data by Wanner method has been done by Tag method and software SOUNDER. The interpretation of field data by Schlumberger method has been done by softwares VES-32 and SOUNDER.

This paper describes the details of the field procedure, interpretation of field data by various methods and software and their comparison and some useful results of the investigation.