In Article " Grounding Design Calculations – Part One ", I indicated the following:
Grounding System Design
Calculations according to type of the building
The procedures for performing the Grounding System Design
Calculations can differ slightly according to the type of the building
as follows:

First: Domestic,
commercial and industrial premises
We mean by domestic, commercial and
industrial premises, all installations up to 1,000 V ac and 1,500 V dc 
between phases, with some minor exceptions.

And I explained Methods of Grounding Design Calculations of Domestic, commercial and industrial premises in the following Articles:
 Grounding Design Calculations – Part One and Grounding Design Calculations – Part Two: Equations Method and solved examples.
 Grounding Design Calculations – Part Three: Nomographs Method
 Grounding Design Calculations – Part Four: Excel Spreadsheets Method
 Grounding Design Calculations – Part Five and Grounding Design Calculations – Part Six: using Tables Method
 Grounding Design Calculations – Part Seven and Grounding Design Calculations – Part Eight: Using Online Earthing Calculators
 Grounding Design Calculations – Part Nine: Software Programs Method
You can preview the following Articles for more info:
Second: High And Medium
Voltage Electricity AC Substations

I began explaining Grounding Design Calculations for second type of buildings: AC Substations in Article " Grounding Design Calculations – Part Ten " where I explained the following:
 Design Procedures for grounding system design as per IEEE 80: Guide for safety in AC substation grounding,
 Step#1: Field Data Collection,
 Step#2: Earthing Grid Conductor Sizing.
Also in " Grounding Design Calculations – Part Eleven ", I explained Step#3: Calculation Of Tolerable Touch And Step Voltages.
Today, I will continue explaining other steps from the design procedures of grounding system for AC Substation.
Design
Procedures of Grounding System for AC Substations  Continued

Step#4: Preliminary Design Of Grounding System

1 Terms Definitions for
Step#4
Notes:

2 Data Needed For Preliminary Grounding System Design
The following Data are needed before starting the preliminary grounding system
design:

3 Typical Configurations For
The Grounding System Of AC Substations
First: Conventional Earthing
Configuration:
The conventional system of Earthing
calls for digging of a large pit into which a GI pipe or a copper plate is
positioned amidst layers of charcoal and salt. It is cumbersome to install
only one or two pits in a day.
Types of conventional Earthing are
shown below:
The conventional system of GI pipe
Earthing or copper plate Earthing requires maintenance and pouring of water
at regular interval. This configuration is inadequate in providing a safe grounding system
for AC Substations.
Second: Earth Mat Design
Configurations:
This design has two configurations as
follows:
Configuration#1:
Several electrodes, such as
ground rods, are connected to each other and to all equipment neutrals,
frames, and structures that are to be grounded; the result is essentially a
grid arrangement of ground electrodes, regardless of the original objective.
If the connecting links happen to be buried
in a soil having good conductivity, this network alone may represent an
excellent grounding system and is suitable for medium size substation.
Configuration#2:
A Substation earth system that have a combination of:
This congiuration#2 has the following
advantages:

4 The Grounding System
Components For AC Substations
Generally, the grounding system for AC
Substations consists of the following components (see fig.2):

5 Preliminary Design Parameters Of Grounding
System Of AC Substations
Many parameters are affecting grounding system design and
performance which are as follows:
Notes:

6 Basic Ideas And Concepts For
The Preliminary design parameters of Grounding System For AC Substations
To establish the basic ideas and concepts,
the following points may serve as guidelines for starting a typical grounding
grid design:
1 For Grid Area:
2 For Ground Mesh Conductors:
3 For Vertical Ground Rods:
However, to get started on the preliminary
design, the following steps can be taken:
Notes:

7 Examples
for Preliminary design parameters of Grounding
System
For AC Substations
By applying Basic Ideas And Concepts For The Preliminary design parameters of Grounding System, we can get preliminary Grid design as in below examples.
Example#1: Square Shape Grid Without
Ground Rods:
A square earthing grid with no ground rods with the following parameters is proposed as shown in Fig (3):
Example#2: Square Shape Grid With
Ground Rods: See Fig (4)
The preliminary design in fig (2) will be modified to include the following parameters:
Example#3: Rectangular Shape Grid With Ground
Rods:
A Rectangular shape grid with ground
rods with
the following parameters is proposed as shown in Fig (5):
Example#4: LShaped Grid With Ground
Rods:
Lshaped grid with ground rods with the following
parameters is proposed as shown in Fig (6):

In the next Article, I will explain Other Steps from the Design Procedures of Grounding System Design for AC Substation. Please, keep following.
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