The construction of a substation will undoubtedly change the properties of any surrounding native soil. In order to study the influence of backfill material on grounding grid performance and in turn optimize that performance, current distribution, electromagnetic fields, ground, and soil structure analysis (CDEGS) was undertaken to simulate the secondary peak of the step voltage generated by a large backfill soil area. As for the various parameters of the finite soil volume, the influence of the soil length L, the edge gradient tan θ, and the resistivity ρ on the secondary peak of step voltage was researched. Then, a grounding test system was established, the selection process of the protection resistors was clarified, and the usage method of agar gel was improved. The feasibility of simulating backfill material with agar gel was verified, and the influence of resistivity and soil scale on the secondary peak of the step voltage was tested. The results show that the larger the backfill material length is, the larger the resistivity is, and the lower the peak voltage is. The effect of soil resistivity on the secondary peak will be greater when the range of backfill material is larger, which means that reducing soil resistivity can effectively reduce the secondary peak. Therefore, a smaller slope can be formed at the edge of the earthwork in the actual substation to reduce the project amount and save investment, which has a certain degree of engineering significance.
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