This paper examines various aspects of the design process and subsequent field test measurements of a large and complex substation grounding system. The study and measurements show that soil layering and lead interference can have a significant impact on the appropriate test location that yields the exact substation ground impedance. Applying a specific percentage rule such as the 61.8% rule for uniform soils to obtain the true ground impedance may lead to unacceptable errors for large grounding systems. This poses significant problems when attempting to validate a design based on raw test data that are interpreted using approximate methods to evaluate substation ground impedance, and determine ground potential rise (GPR), touch and step voltages. Advanced measurement methodologies and modern software packages were used to obtain and effectively analyze fall of potential test data, compute fault current distribution, and evaluate touch and step voltages for this large substation. Fault current distribution between the grounding system and other metallic paths were computed to determine the portion of fault current discharged in the grounding system. The performance of the grounding system, including its GPR and touch and step voltages, has been accurately computed and measured, taking into account the impedance of the steel material used of the ground conductors and circulating currents within the substation grounding system.
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 J. Ma and F. P. Dawalibi, “Effects of Inductive Coupling between Leads in Ground Impedance Measurement Using Fall-of-Potential Method”, in Proc. IEEE/Power Eng. Soc. Trans. Dis. Conf. Expo., New Orleans, LA, Apr. 11-16, 1999, pp. 266-271.
 Y. Li, J. Ma and F. P. Dawalibi, “Impedance Measurement of Large Grounding Systems Using the Fall-of-potential Method,” Proceedings of the Third IASTED International Conference on Power and Energy Systems, EuroPES 2003, Marbella, Spain, Sept. 3-5, 2003, pp. 701-706.
 G. Yu, J. Ma and F. P. Dawalibi, “Effect of Soil Structures on Grounding Systems Consisting of Steel Conductors,” Proceedings of the International Conference on Electrical Engineering (ICEE'2001), Xian, China, July 22-26, 2001.
 Y. Li, J. Ma and F. P. Dawalibi, “Power Grounding Safety: Copper Grounding Systems vs. Steel Grounding Systems,” International Conference on Power System Technology (POWERCON2006), Chongqing, China, October 22-26, 2006.
 Y. Li, F. Dawalibi, J. Ma and Y. Yang, “Analysis of A Steel Grounding System: A Practical Case Study,” The 15th Conference on Electric Power Supply Industry (CEPSI) Shanghai, China, October 18-22, 2004.
 Y. Li and F. P. Dawalibi, “Practical and Realistic Considerations of Fault Current Analysis,” Proceedings of the International Conference on Electrical Engineering (ICEE 2011), Hong Kong, July 10 - 14, 2011.