Impedance Measurement of Large Grounding Systems using the Fall-of-Potential Method

Y. Li, J. Ma, and F.P. Dawalibi (Canada)


Transmission and Distribution, Ground Resistance, Fallof Potential, Impedance Measurement


This paper discusses the measurement of ground impedances of large grounding systems using the Fall-of-Potential method. Several interesting curves that represent the exact potential probe locations for typical large grounding system scenarios have been presented. The results show that applying the 61.8% rule for uniform soils to obtain the true ground impedance may lead to unacceptable errors for large grounding systems. The soil structures considered include uniform and two-layer types. The paper also presents a technique used to measure the grounding grid impedance of a substation (or power plant) that may be interconnected to external grounding systems. The results presented in this paper offer guidance to estimate the exact location of the potential probe required to measure the ground impedance of a large grounding system.

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