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Substation Grounding and Step Over Native Concerns

By Molli Dooley

Abstract

Substations are designed with grounding systems with one function: to reduce touch and step voltages inside the substations. IEEE Std 80 is most often used to determine compliance for step and touch voltages and clearly applies within a substation fence. Outside of the substation fence, there is a breakpoint where substation surfacing is no longer installed. For that area beyond the substation surfacing, additional step over native analysis may need to be performed. While IEEE Std 80 focuses on human safety, it is vague about the analysis and mitigation required beyond the substation fence. The methodology in the guide does not analyze voltages outside the grounding system area, but the guide discusses the need to consider other areas. In a survey conducted by the IEEE Std 80 working group, roughly 50% of utilities evaluate step over native beyond the substation fence. While step over native concerns are rare, they can be incredibly costly to mitigate.

This paper focuses on the basics of substation grounding as well as providing background on step over native soil (outside the station). With this knowledge the decision of whether to study and mitigate for these conditions can be made by individual utilities.

Paper presented at the 50th annual Transmission & Substation Design & Operation (TSDOS) Symposium in Frisco, Texas.

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