The Impact of Substation Grounding Grid Design Parameters in Non-Homogenous Soil to the Grid Safety Threshold Parameters

Abstract

It is important to ensure that a grounding system is designed with a low magnitude of earth resistance, so the protection system can divert the large fault current to earth effectively. The performances and protection level of a grounding system need to be acknowledged as the condition of soil structure changes with different soil characteristics. At present, there is a lack of systematic guide or standards for grounding grid designs that consider non-uniform soil and its impact on the grounding systems. By computing the grid safety threshold parameters consisting of the grid impedance, step, and touch voltages, a comparison has been made between uniform soil and two-layer soil models. Where the competence and level of safety of the grounding systems depend on the soil attributes, the significant impact of various soil conditions is seen. The evaluations on performance and safety assessment in two-layer soil conditions hold the novelty and originality as there is no such comparison and discussion have been made to date. These comparisons would help in forecasting the behavior and safety of the grounding system in various soil environments, which would provide engineers with additional expertise to design an effective and secure grounding system. This research would contribute to the existing body of knowledge by differentiating and predicting the performance of a grounding system when the characteristics of the soil differ significantly from uniform soil as most of the standards and guidelines only consider uniform soil while designing a grounding system, owing to its complexity at the site. INDEX TERMS grounding grid impedance, step voltage, touch voltage, multilayer soil, uniform soil, non-homogeneous soil.

Assessment of the Grid Safety Values for Substation Grounding Grid Design Parameters in Vertical Two-Layer Soil Structure

“…Figure 23 shows the impedance reduction of 61% from 50 m × 50 m to 130 m × 130 m grid size (A2 and A3) in a 75% soil ratio of a vertical two-layer soil is lower compared to the percentage of impedance reduction of 77% of the same grounding grid placed in a horizontal soil layer with a high soil resistivity top layer as can be seen for grid impedance in Figure 26 (Permal et al, 2021). The difference in the percentage of impedance reduction in horizontal and vertical two-layer soil shows that the soil structure impacts the grounding system's behavior.…”

“…Figure 20. Grid impedance graph for increasing vertical rod length in horizontal two-layer soil (Permal et al, 2021) Influence of length of rods on grid impedence Pertanika J. Sci. & Technol.…”

A Method for Calculating Grounding Resistance of Reinforced Concrete Foundation Grounding Systems

“…However, due to the complex structure of the reinforced concrete foundation, establishment of the simulation model for one pile is troublesome and the computation is extensive, not to mention that usually the foundation consists of several piles. The grounding resistance of the cylindrical conductor can be quickly calculated by the method Energies 2022, 15, 4607 2 of 10 of moments even if the structure is complex [15][16][17]. For this reason, some methods to equate non-cylindrical electrode to cylindrical electrodes have been proposed in order to use the method of moments to calculate grounding resistance.…”

“…Energies 2022, 15, x FOR PEER REVIEW 2 of 10 grounding resistance of the cylindrical conductor can be quickly calculated by the method of moments even if the structure is complex [15][16][17]. For this reason, some methods to equate non-cylindrical electrode to cylindrical electrodes have been proposed in order to use the method of moments to calculate grounding resistance.…”

Influence of Lightning Current Parameters and Earthing System Designs on Tower Footing Impedance of 500 kV Lines

“…The system failure due to BFO is measured as a back-flashover rate (BFR) that is typically related to high tower footing impedance and soil resistivity. The tower footing impedance associated with soil resistivity is known to have a significant effect on transmission system failure [7][8][9]. Usually, the value of the impedance parameter must be less than the limit of the tower impedance set by the requirement of the power utility industry.…”