Optimization and assessment of substation grounding grid designs in non-homogeneous soil conditions

• Main Author: Navinesshani A/P Permal, Dr.
• Format: text::Thesis
• Language: English
• Published: 2023
• Subjects: Optimization and assessment of substation grounding grid designs in non-homogeneous soil conditions

The purposes of a substation grounding system are to establish the lowest impedance path for unwanted fault current and protect both personnel and power equipment from electrical shock and overvoltage, respectively. The earth is made up of different compositions with different soil characteristics that may vary from layer to layer, potentially affecting the safety parameters (grounding impedance, step, and touch voltages). As a result, the soil characteristics in which the grounding system is buried must be identified and assessed. Multiple soil layers are often ignored while designing a grounding system because of the complexity of the numerical computations involved which results in significant inaccuracies. Thus, an assessment of grounding behaviour in homogeneous and non-homogeneous soil conditions (two-layered horizontal and vertical soil), with different soil characteristics on the grounding system performances using Current Distribution, Electromagnetic Fields, Grounding and Soil Structure Analysis (CDEGS), has been presented in this research. The goal of the assessment is to highlight the differences or similarities in grounding behaviour between different soil conditions. The main parameters accountable for grounding system behaviour can be categorized into the designs of the grounding system, including the grid size, mesh sizes, the number and length of vertical rods, and the characteristics of the earth (soil structures and resistivity) in which the grounding grids are established. The grounding design parameters influence the behaviour and safety of the grounding system which differ depending on the soil condition. Although an exact comparison is impossible due to the dependency of the grounding grid designs on the installation location, the fundamental outcomes of the grounding behaviour as the grid designs and the soil characteristics vary shall be beneficial in providing more information on the grounding designs in non-homogeneous soil. One of the important findings of the assessment shows that designing a grounding system in horizontal two-layer soil requires more attention compared to vertical two-layer and homogeneous soil conditions because the soil properties such as top soil height and its resistivity influence the grounding behaviour significantly with varying grounding design parameters. The overall findings can serve as an important guide on the adequate and safe substation grounding grid design for the general public and personnel. Moreover, a good grounding system should not only be efficient but also economical. An optimisation method established from the Simulated Annealing (SA) algorithm is applied to search for an optimal grounding design solution. Although there are many research studies conducted by researchers on optimisation, there is very limited research on the problem of grounding grids in two-layer soil, particularly in vertical soil structures. The proposed optimisation’s results show that the total length of conductors in a grounding grid can be optimised from the initial length of about 33.71 % in homogeneous soil, 6.43 % in horizontal two-layer soil, and 5.67 % for vertical two-layer soil structure without jeopardizing the grounding’s safety. Besides, the proposed technique would be able to utilize square and rectangle-shaped grounding grids with several grid conductors and vertical rods to be optimised in homogeneous, two-layer horizontal and vertical soil structures, depending on the resistivity of the soil.