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.
And in Article " Grounding Design Calculations – Part Twelve ", I explained Step#4: Preliminary Design of Grounding System for AC Substations.
And In Article " Grounding Design Calculations – Part Thirteen ", I explained Step#5: Calculation of the Preliminary Grid Resistance, Rg, Of the Grounding System in Uniform Soil
And In Article " Grounding Design Calculations – Part Fourteen ", I explained Step#6: Determination of Maximum Grid Current, IG.
Also, in Article " Grounding Design Calculations – Part Fifteen ", I explained the following steps:
 Step#7: Calculation of Maximum Grid Potential Rise and Comparing With the Tolerable Touch Voltage from Step#3
 Step#8: Calculation of Mesh 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#9: Comparing
The Computed Mesh Voltage From Step#8 With The Tolerable Touch Voltage From
Step#3

Step#10:
Comparing The Computed Step Voltage From Step#8 With The Tolerable Step
Voltage From Step#3

Example#1:
Using the same data of Example#2 in previous
Article Grounding Design Calculations – Part Fifteen verify that the earthing grid design is safe or not.
Solution:
From example#2 referred above, we get the following
results:
Step#1: Comparing
the Computed Mesh Voltage E_{m} with the Tolerable Touch Voltage Etouch
We find that: E_{m} < Etouch
So, the earthing system passes the touch potential
criteria and we will Continue to Step#10: Comparing the
computed step voltage from step#8 with the tolerable step voltage from step#3
Step#2: Comparing The Computed
Step Voltage E_{s} With The Tolerable Step Voltage Estep
We find that: E_{s} < Estep
So, the earthing system passes
the touch potential criteria and we will
Move to Step#12: Detailed final design.
Having passed both touch and
step potential criteria, we can conclude that the earthing system design is
safe.

Step#11:
Preliminary Design Modification
If either the step or
touch tolerable limits from step#3 are exceeded, revision of the grid design
is required. These revisions may include modifying the following design
parameters:

Methods for Preliminary Design Modification
If the calculated grid
mesh and step voltages are greater than the tolerable touch and step
voltages, then the preliminary design needs to be modified. The following are
possible remedies:
1 Decrease Total Grid
Resistance:
If the total grid
resistance is decreased, the maximum GPR is decreased; hence the maximum
transferred voltage is decreased. effective ways to decrease the grid
resistance are:
2 Decrease Grid
Spacings:
By increasing the number
of parallel conductors in each direction, the condition of the continuous plate can
be approached more closely. Dangerous potentials within the substation
can be eliminated. For the perimeter, the effective ways to control perimeter
gradients and step potentials are:
3 Increase the thickness
of the surface layer: a practical limit may be 6 inches.
4 Limit total fault
current: If feasible, limiting the total fault current
will decrease the GPR and gradients in proportion.
5 Diverting greater
part of the fault current to other paths by one of the following methods:
6 Barring access to limited
areas: if practical, can reduce the probability of hazards to
personnel.
7 Consider
soil treatments to lower the resistivity of the soil.
8 Greater use
of high resistivity surface layer materials.

Step#12:
Detailed Final Design
After satisfying the step
and touch voltage Criteria, we come to finalize our grounding grid design
which should be reviewed to:
The result
of this investigation may require additional grid and ground rods /conductors
especially if:
The most important areas of concern are:

Important Areas Of Concern
1 Service Areas:
They include the areas within the
substation fence that used for storage, staging, or general service areas.
Step and touch potentials should be checked to determine if additional
grounds are needed in these areas.
2 Switch Shaft And Operating Handle
Grounding:
Operating handles of switches represent a
significant concern of electrical
shock if the handles are not adequately grounded. So, touch and step voltages
near the operating handle should be within safe limits. Additional means are
taken to provide a greater safety factor for the operator as follows:
3 Grounding Of Substation Fence:
The substation grounding design should be
investigated that the touch potential on the fence is within the calculated
tolerable limit of touch potential. Step potential is usually not a concern
at the fence perimeter, but should be checked to verify that a problem does
not exist.
The metal fence grounding requirement may
be accomplished by:
As per The National Electrical Safety Code
(NESC), the various fence grounding practices are:
Several different practices are followed
for fence grounding which are (see fig.4):
However the following notes must be
considered when grounding a substation fence:
4 Control Cable Sheath Grounding:
Metallic cable sheaths, unless effectively
grounded, may attain dangerous voltages with respect to ground. These voltages
may result from:
Metallic cable sheaths are grounded by
connecting wire or strap to the permanent ground, the used wire or strap must
be sized to carry the available fault current.
However the following notes must be
considered when grounding Control cables:
5 GIS Bus Extensions.
6 Surge Arrester Grounding:
Surge arresters should always be provided
with a reliable lowresistance ground connection by one of the following
methods (see fig.6):
However the following notes must be
considered when grounding Surge arrester:
7 Separate Grounds:
The practice of having separate grounds
within a substation area is rarely used for the following reasons:
8 Transferred
Potentials:
A serious hazard may result during a ground
fault from the transfer of potential between the substation ground grid area
and outside locations (see fig.7). This transferred potential may be
transmitted by communication circuits, conduit, pipes, metallic fences,
lowvoltage neutral wires, etc. The danger is usually from contact of the
touch type. A transferred potential problem generally occurs when a person
standing at a remote location away from the substation area touches a
conductor connected to the substation grounding grid. The importance of the
problem results from the very high magnitude of potential difference, which
is often possible. This potential difference may equal or exceed (due to
induced voltage on unshielded communication circuits, pipes, etc.) the GPR of
the substation during a fault condition.
Various means can be taken to protect
against the danger of transferred potentials for :

What is done after finishing the detailed final design of the
substation grounding system as a paper work?
After the detailed final
design of the substation grounding system is finished , the following steps
are usually followed:

In the next Article, I will explain and introduce the best ever excel spreadsheet for Grounding System Design for AC Substation. Please, keep following.
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