Simplified Analysis of Electrical Gradients Above a Ground Grid-I How Good Is The Present IEEE Method? (A Special Report For WG 78.1)

Referring to the 1976 edition of IEEE Std 80, this paper examines the basic premises of IEEE gradient method and of simplified equations for determining the touch and step voltages in the corner mesh of a grounding grid. Re-examination of the prirncipal assumptions yields a new simiplified formula for Km which performs the calculation with less error. A beneficial effect of ground rods is evaluated in view of the present equation for the current irrregularity factor Ki. A brief analysis of the effect of a crush-stone overlay upon the allowable surface voltage above and beyond a grounding grid, is also icluded. A review of work done by others related to the methods of Std 80 includes a discussion of equations and of some critical aspects involved. A computer-produced series, comparing the performance of the old simplified and non-simplified equations for-Km with the improved ones and with the equations suggested by Thapar and Nagar, Zuker- man, Zink, and Nahman, concludes Part I of this two-part report. Its purpose is to provide a framework for updating and refining Appendix of the Guide which is presently under revision.