Earth-resistance measurement of large electrodes, carried out by the fall-of-potential method, can involve difficulties and errors. To eliminate these disadvantages, the authors have developed a systematic analysis of different grounding systems buried in nonhomogeneous soils. The analysis is made by using a computer program based both on Maxwell's subareas method and on the method of electric images; the soil is represented by a two-layer equivalent model with known parameters. This paper shows the computer program theory in full. Moreover, systematic analysis provides numerous curves allowing accurate measurements of the earth resistance of large grounding systems with often-used shape when the auxiliary current electrode is located near the grounding system under test. Finally, the authors show that the given curves can also be used for earth-resistance measurement of those systems whose shapes are different. In conclusion, this paper supports the contents of IEEE Standard 81-1983 and extends its application range.
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