الفهرس 
chapter 1Only 14 pages are availabe for public view
 |  | from | 284 |  |  |
| | | from | 284 | | |
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.