الفهرس | Only 14 pages are availabe for public view |
Abstract In order to realize a safe grounding system design, vertical ground rods, as well as, grounding grids are the simplest and commonly used means. The addition of the vertical ground rods to the grounding grid achieve a convenient design for grounding system to improve the performance of it by reducing not only the grid resistance but also the step and touch voltages to values that safe for human. The grounding resistance is one of the most important parameters of ground grids; thus, the current distribution among various parts of substation grounding systems has been affected by different parameters of grounding systems. This thesis presents a new contribution to obtain the current distribution of grounding grid conductors with and without vertical rods buried in two layers soil. The two-layer soil model has been simulated mathematically using two suitable values of resistivity. The computations of current distribution have been based on the current for each segment of meshes. The investigation includes different meshes, such as one mesh, four meshes, and nine meshes and/or also other more meshes. The calculation technique of current distribution is carried out to give all the mutual resistances respecting to (x,y,z)coordinates of each segment to solve the equation problems containing all segment currents of meshes. The indicated results of this contribution give the current distribution for each segment of each mesh with and without driving rods. The effect of vertical rods, which has connected to horizontal grounding grid on current distribution and grounding resistance for different groundinggrids dimensions and shapes, has been studied in this thesis. An experimental model to simulate two-layer soil is presented also for the validation of the calculated results. Corrosion of the grounding grid is the most defective parameter, which has affected the grounding grid performance and its ability to ensure its main target of stability and safety of the electrical systems. In order to indicate the corrosion degree of the grounding grid and its effect on the grid current distribution plus the grounding grid lifetime, a mathematical model has been investigated in this thesis. It has been applied to different shapes of steel grounding grids buried in two layers soil. Moreover, an experimental study has been carried out also to investigate the relationship between the corrosion degree and the contact resistance of the galvanized steel grounding grid with different shapes at low resistivity conditions. Cathodic protection can be defined as the reduction of corrosion rate by shifting the corrosion potential of the electrode toward a less oxidizing potential by applying an external electromotive force. Description of cathodic protection, forms, types of anode material, selection of their material, their lifetime, the comparison between cathodic protection types, limitations that must be kept in mind and designing steps in details and their application on different shapes of grounding grids are investigated in this thesis. For increasing the flexibility of the calculations, per unit system has been used in this thesis. |