A New Methodology for the Grounding Design of Transmission Lines and Windfarm Towers

TL or WF. The justification for this approach rests on the understanding that individual geophysical soundings do not accurately reflect the subsurface geoelectrical structure, as they are affected by noise, non-uniform ground conditions, and distortions inherent to the sounding method. These deviations present a Gaussian distribution in the log-space; therefore, a statistical treatment of the set of apparent resistivity curves can significantly reduce the individual curve’s deviations. The proposed methodology can be applied to any distributed grounding system and has already been applied to several TL and WF tower grounding projects.

This methodology, rather than handling numerous low-accuracy geoelectric models, uses only up to five ground models and their corresponding grounding phases. The paper begins by presenting the proposed methodology and a test case. The sources of distortion in the apparent resistivity curves are then analyzed, thereby justifying the proposed method. The application to the test case begins with the calculation of the geometric-average apparent resistivity curve using all available sounding lines for the tower locations. Calculated curves with one and two standard deviations above and below the general average curve are then used to define up to five apparent resistivity curves (the standard curves), which delimit the apparent resistivity ranges. Inverting this set of standard curves yields up to five geoelectric models associated with the corresponding grounding geometries, which define the counterpoise wire lengths required to achieve the projected tower resistance for the different soil structures along the TL.