Abstract
To balance the potential distribution on the surface of a substation, an equal spacing arrangement of the grounding grid conductors is not an economical solution. The implementable solution is an unequal placement of its constituent elements. The design methodologies of such a configuration are complex and require computer-assisted numerical analysis. This paper proposes and validates a very simple method, based on an arithmetic progression, of arranging the conductors of the grounding grid that guarantees the reduction of touch and step voltages, ensures the efficiency of the material used and has no limitations on its applicability for atypical substation surfaces (too large or too small), respectively for few or many parallel conductors. To certify the method, the proposed algorithm is analyzed, through the CYMGRD Substation Grounding Program, and compared to the technologies currently applied, for the substation grounding grid presented as an example in the IEEE Guide for Safety in AC Substation Grounding 80™- 2013 standard.
Highlights
The optimized design of a grounding system related to a substation involves the fulfillment of the requirements regarding: the ground resistance, Rg, touch voltage, Et, and step voltage, Es, under the conditions of a minimum of material and labor involved
The simplest and only one that benefits from validated analytical relationships that allow the determination of the variables mentioned above, is that of a grounding grid with equal spacing arrangement (GG-E)
Even by adding vertical electrodes, the 12 steps design procedure recommended by [1] leads to a configuration with which the imposed touch voltage is satisfied in an uneconomical way
Summary
The optimized design of a grounding system related to a substation involves the fulfillment of the requirements regarding: the ground resistance, Rg, touch voltage, Et, and step voltage, Es, under the conditions of a minimum of material and labor involved. Equalizing the ground potential distribution could be achieved with a grounding grid with unequal spacing arrangement (GG-U) of the parallel conductors that create the grid in both directions of the substation area For such systems, the well-known Sverak [2] or alternately Schwartz’s equations [3] (based on Sunde [4], Rudenberg [5] works and improved by Kercel [6]) for ground resistance give acceptable results, approx. The relations used to calculate the maximum step and mesh voltages [1] have no applicability for other configuration except the equal spacing one In such circumstances, all methodologies for determining unequal distances between conductors that minimize the values of touch and step voltages are dependent on computer-assisted numerical analysis. Where k is the segment number counted from the central mesh, dmax is the spacing of the central mesh:
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