Journal of Recent Trends in Electrical Power System
Volume 6 Issue 3
DOI: https://doi.org/10.5281/zenodo.10043497
ac
Enhancement of the Grounding System of 132/33 kV Subtransmission Station via an ETAP-Based Approach
Hachimenum Amadi, Peter Nwauju, Dikio Idoniboyeobu
Department of Electrical Engineering, Rivers State University, Port-Harcourt, Nigeria
*Corresponding Author
E-Mail Id: hachimenum.amadi@ust.edu.ng
ABSTRACT
Using the IEEE approach for grounding design and ETAP software for system modelling,
this study seeks to enhance the grounding system at the 132/33kV Afam 1 Sub-transmission
station. To get the desired effects, the touch voltage, step voltage, and mesh voltage are
chosen. The findings indicate that the current grounding system of the station is in terrible
shape. Three of the six grounding pits of the station have been undermined, two have been
vandalised, and the one pit that is still in place is insufficient to support the station. Based on
the results of the violations, the earth resistance values for Pits 1, 2, and 3 are 2.63, 1.25, and
1.16, respectively. The study used 1.5 bags of salt, six bags of ashes and some water to
reduce soil resistance in pits 1, 2, and 3. Soil resistance in pits 1, 2, and 3 was reduced to
0.67, 0.59, and 0.5, respectively, after treatment, resulting in a 70% reduction in resistivity.
Pits 4 and 5 require the installation of new grounding systems in place of existing ones. The
grid structure of the sub-transmission station comprises squares that are 100 m by 90 m in
size, making a total mesh area of 9000 m. The X-axis has 18 conductors, and the Y-axis has
19 conductors. The grid conductor was buried at depth of 0.6 metres, its diameter is 16
millimetres, its total length is 5972 metres, the crushed rock thickness is 1 metre, there are
280 ground rods, and each earth rod is 3 metres long. The station's ground rod spacing is 8
metres. The investigation also discovered that for a 70-kilogramme person with a 0.5-second
fault length and a 0.6 current division factor, a fault current of 13785A and a touch voltage
of 557.3 Volts were calculated. The temperature at which the thermal coefficient of resistance
is zero degrees Celsius, the ambient temperature and the maximum temperature are all fixed
at 40 degrees Celsius. The allowable touch voltage and the permitted step voltage at the fault
location must be 529.29 and 450.87 volts, respectively, based on the 3-kA ground shortcircuit current and the 15 ratio. The ground potential rise (GPR) was 2098.7 Volts, the
permitted step voltage was 2823.6 Volts, and the actual step voltage was 205.4 Volts. The
grid works safely because the GPR is within allowable bounds. From the findings, treating
the soil resistivity in pits 1, 2, and 3 and replacing the grounding systems in pits 4 and 5
outrightly are the best ways to stop electrical failures and fatalities. The study recommends
that the station earth resistance be checked annually using an earth resistance tester.
Keywords: Earthing, earthing system, grounding system, optimization, sub-transmission
station, transmission
INTRODUCTION
When working near earthed equipment and
facilities, people must be protected from
electrical shock by having the electrical
system earthed [1]. The configuration,
chemical makeup, wetness, temperature,
season, depth, diameter, and other
characteristics of the ground, which serves
as an electrical conductor, can all affect the
conductivity of the ground [2]. A
homogeneous electrical potential on the
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ground that is close to absolute zero is
what an earthing structure is meant to
achieve [3]. Its reference system, however,
may experience voltage changes due to the
earth's natural variations [4]. The
resistance of the earth resistance and the
intensity of the fault current both affect
this variation, which is known as the Earth
Potential Rise (EPR). For an earthing
system to be functional, the ground
resistance must be as low as possible to
reduce the EPR. The allowable resistance
levels for distribution substations might
range from 1 to 5 Ohm, depending on the
local circumstances [5].In the past,
earthing power transformer substations
involved a labour-intensive process of
digging a large pit, inserting grounding
rods, and connecting them to the power
transformers and substation hardware. The
resistance of grounding electrode systems
can greatly vary due to various factors
such as electrode resistance, rod surface
area, rod size, and electrode material
composition [6]. Adherence to proper
grounding standards is crucial for
transmission lines and substations. A welldesigned regularly maintained earthing
system with ample room for future growth
is essential for its reliable and efficient
functioning. It's important to ensure the
earthing system is both reliable and futureproof.
For the safety of an electrical station or
substation and its users, an appropriate
earthing system must be designed and
installed [7]. To safeguard against
electrical outages and lightning strikes as
well as to guarantee the proper operation
of control and protection systems, an
efficient earthing system is required.
Strong currents, such as those caused by
lightning strikes, can be safely redirected
to the ground with the use of the earthing
system [8]. The substation and its users are
at risk of damage or even death without a
properly constructed edging system [5].
Given that electricity forms the basis for
Journal of Recent Trends in Electrical Power System
Volume 6 Issue 3
DOI: https://doi.org/10.5281/zenodo.10043497
numerous
scientific
and
social
advancements,
its
significance
in
contemporary
society
cannot
be
emphasised [9]. The preservation of
human life is paramount and an earthing
system is necessary to ensure safety within
and around the substation.
If the grid design does not fulfil these
standards, it is advised to minimise the
available ground fault current to enhance
the power quality of a system and adhere
to regulatory limits for tolerable touch
voltage [10]. When a system is connected
to a metal object that is buried in the
ground and allows electricity to pass
through the earth, the system is said to be
grounded [5]. According to Reference,
[11], power quality is the degree to which
the parameters of the power supply,
including voltage, frequency, and others,
adhere to legal restrictions. The electrical
station system’s neutral and the earth
create
a
low-impedance
electrical
connection for the grounding system [12].
To ensure that people and other living
things can safely touch metal objects
connected to the system's neutral, the
earth's potential in a three-phase system
must be of the same value as the neutral's
potential. To ensure low resistivity, it is
crucial to take into account changes in soil
resistivity when designing a grounding
system. Soil resistivity is a critical element
in the performance of a grounding system
[13].
Modern substation system design now
places a significant emphasis on the value
of reliable grounding systems. To ensure
the dependability of electric power
generation, transmission and distribution,
grounding is essential [14]. Protect people,
equipment, and power users from lightning
strikes or electrical fault currents and helps
to avoid high voltage spikes during
disturbances. In order to ensure the safe
and dependable operation of the electrical
power system, grounding is crucial.
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To lessen the voltage spike that occurs
after
a
malfunction,
high-voltage
substations need to have extraordinarily
low ground resistance. The most common
method for accomplishing this is the
deployment of interconnected ground
networks [15]. In corrosive soils with high
dampness, salt substance, and temperature,
ground poles and their associations are
susceptible to corrosion over the long run.
Journal of Recent Trends in Electrical Power System
Volume 6 Issue 3
DOI: https://doi.org/10.5281/zenodo.10043497
Even if the resistance of the grounding
system was initially modest, it may
increase if the ground rods begin to
corrode [16]. The earthing solution for
sub-transmission stations presented in this
study is useful and efficient, and it can
stop dangerous voltage spikes in both
normal and abnormal circumstances. A
comprehensive assessment of the soil
resistivity in your area is provided in Table
1 below.
Table 1: Guide to Soil Resistivity (Ω·M).
Type of soil
Climatic Condition Normal and
high rainfall
Range of values
Alluvium and lighter clays
Depends on water level of locality
Clays
5 to 20
Marls
10 to 30
Porous Limestone
30 to 100
Porous Sandstone
30 to 300
Quartzites,
compact
and 100 to 1000
crystalline limestone
Clay slates and slatey shales
300 to 3000
Granite
1000
Fissile states, schist, gneiss and 1000 upwards
igneous rocks
Source: [17]
On-site measurement is required to
establish the soil resistivity precisely. This
is essential because the soil is important in
the distribution of the fault current. To
adequately protect against earth faults,
field data such as soil surface layers and
underlying geological structures should be
gathered. In order to determine the
viability of the protection system based on
the buried depth and substance of the earth
electrodes being utilized, the stratification
of the soil should also be analysed. The
ideal location for the substation should be
determined using a feasibility analysis,
taking into account the soil resistivity,
even though it may not be feasible to
change the underlying soil qualities. The
following is the recommended list of
locations for substations:
Underground
waters
Range of values
1 to 5
2 to 5
30 to 100
(i) Wet sand, peat, and marshy soils;
(ii) Clay, clayey soil, arable and loamy
land, or mixed and composite of small
sands;
(iii) Loamy clay and composite of small
stones, sands, and gravels.
The following specifications should be
taken into account when choosing a
conductor material for underground use:
 Ability to withstand all weather
conditions.
 Adequate current carrying capacity for
all currents and durations in both
normal and fault operation settings.
 Capability
to
discharge
highfrequency currents to lower surge
impedance.
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Journal of Recent Trends in Electrical Power System
Volume 6 Issue 3
DOI: https://doi.org/10.5281/zenodo.10043497
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
Capability to carry current at all
temperatures in both normal and fault
states.
MATERIALS AND METHOD
The grounding system of the 132/33kV
Afam 1 Sub transmission station was
enhanced by utilising data gathered from
the Transmission Company of Nigeria
maintenance unit. This information
included data on the earthing conductor,
the earth mat, the earth connectivity, the
earth electrode, the grid design, the soil
resistivity, and the surface layer using step
and touch potentials. An earthing mat that
satisfied the specifications of the earthing
system and was within the permitted
ranges for the step potential, touch
potential, and transfer potential was
produced using the simulation software
known as the Transient Analyser
Programme (ETAP).
The study deployed the electrical transient
analyser programme (ETAP) simulation
software and the Institute of Electrical and
Electronic Engineers (IEEE) technique in
the design of the station earthing system.
The earthing system dimension is 100 x 90
meters and the average soil resistivity is
assumed to be 57.4 meters. It is important
to take the surface layer of high resistivity
area into account when building the
earthing grid to ensure safety and
protection against the current in the station
with high resistivity top/lower soil.
Touch Potential
According to reference [10], there is a risk
of dangerous voltage gradients in the earth
near a power generation site, when there
are no alternative channels for earth faults,
but the earth itself, which can cause
electrical shock hazards. These hazards
include touch voltages, which are the
potential difference between the earth and
a metallic object that a person is touching,
and step voltages, which are the voltage
gradient between two feet that are planted
firmly on the ground. The earthing grid
helps to mitigate these hazards by lowering
voltage gradients and distributing fault
currents to remote earth [18]. Engineers
use calculations of touch and step
potentials to determine if the earthing grid
is capable of dissipating fault currents and
preventing dangerous touch and step
voltages.
Fig. 1: The 132/33KV Afam I Sub-transmission Station [18].
The mesh voltage,
, was subsequently determined [18]:
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Journal of Recent Trends in Electrical Power System
Volume 6 Issue 3
DOI: https://doi.org/10.5281/zenodo.10043497
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(1.1)
V
Given height h= 0.472m and spacing between conductors D= 5 m and n= 7.363.
Spacing Factor for Step Voltage
In finding the step factor, we have:
[
(
)]
Step Potential
Whenever compared to the touch potential,
the step potential is frequently of a lesser
magnitude as the ground is touched
sequentially by the feet. The human body
can endure a greater current when
subjected to an electrical shock due to the
current flow transpiring between the feet
(1.2)
as opposed to through vital organs such as
the heart. The step potential must be less
than the step voltage criteria to create a
secure earthing system. The step potential
E s is represented in [19] and found
as follows:
(1.3)
RESULTS AND DISCUSSION
By modifying the voltages based on
variables such the soil resistivity, soil
layer, and shock current duration, ETAP
simulation software allows for the
achievement of the target soil resistivity
level of 2500 ohm-meters. Any unwanted
circuit's maximum voltage must not be
higher than the step voltage and touch
voltage restrictions. This design features a
100-meter by 90-meter square grid
configuration with a total mesh area of
9000 square meters, ground rod spacing of
8 meters, grid conductor burial depth of
0.6 meters, grid conductor diameter of 16
millimetres, 18 conductors in the x-axis,
19 conductors in the y-axis, total
conductor length of 5972 meters, 1 meter
of crushed rock thickness, and 280 ground
rods with a length of 3 meters each, as
illustrated in Figure 2.
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Journal of Recent Trends in Electrical Power System
Volume 6 Issue 3
DOI: https://doi.org/10.5281/zenodo.10043497
Fig. 2: The Earthing Pit Position in the 132/33KV Afam 1 Sub-transmission Station [18].
Fig. 3: The Distance and the Violated Earth Pit 1 Resistance Rating.
The result shown in Figure 4 indicates that the actual earth resistance value for Pit 2 that has
been violated is 1.25Ω.
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Journal of Recent Trends in Electrical Power System
Volume 6 Issue 3
DOI: https://doi.org/10.5281/zenodo.10043497
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Fig. 4: The Distance and the Violated Earth Pit 2, Resistance Rating.
The 132/33kV Afam 1 sub-transmission
station's earthing system is in disrepair,
with three of the substation's six earthing
pits broken, two vandalised, and the
remaining pit unable to provide
appropriate service. For pits 1, 2, and 3,
the soil resistivity was treated with six
bags of ashes and 1.5 bags of salt and
water, resulting in a 70% reduction in soil
resistivity. New earthing systems need to
be installed in pits 4 and 5. The treated
earth resistance values for Pits 1 and 2 are
0.67 and 0.59, respectively, according to
the data illustrated in Figures 5 and 6 and
Tables 2 and 3 [18].
Fig. 5: The Distance and the Treated Earth Pit 1 Resistance Values.
The result shown in Figure 6 indicates that the actual earth resistance value for Pit 2 that has
been treated is 0.59Ω.
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Journal of Recent Trends in Electrical Power System
Volume 6 Issue 3
DOI: https://doi.org/10.5281/zenodo.10043497
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Fig. 6: The Distance and the Treated Earth Pit 2. Resistance Values.
Table 2: The Distance and the Treated Earth Resistance Values of Pit 1 [18].
Distance Resistance
S/No.
(M)
(Ω)
1
4
0.75
2
8
0.67
3
12
0.84
Actual
Earth
Resistance for 0.67
Pit 1
Table 3: The Distance and the Treated Earth Resistance Values of Pit 2 [18].
The result shown in Figure 7 shows the difference between the violated earth pit and the
treated earth pit 1, indicating that the resistance of pit 1 is 100% normal.
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Journal of Recent Trends in Electrical Power System
Volume 6 Issue 3
DOI: https://doi.org/10.5281/zenodo.10043497
Fig. 7: The difference between the violated and treated earth pit 1 resistance (Ω).
The result shown in Figure 8 illustrates the difference between the violated soil pit and the
treated soil pit 2, indicating that the resistance to pit 2 is 100% normal.
Fig. 8: The difference between the violated and treated earth pit 2 resistance (Ω).
Table 4: The difference between the violated and treated earth pit 1 resistance (Ω).
DISTANCE (M) Violated RESISTANCE (Ω) Treated RESISTANCE (Ω)
I4
4.39
0.75
8
3.21
0.67
12
2.63
0.84
Table 5: The difference between the violated and treated earth Pit 2 resistance (Ω).
DISTANCE (M) Violated RESISTANCE (Ω) Treated RESISTANCE (Ω)
4
1.27
0.59
8
1.25
0.75
12
1.39
0.64
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CONCLUSION
AND
RECOMMENDATIONS
The IEEE approach was used to model and
simulate the 132/33KV sub-transmission
substation with the aid of the Electrical
Transient Analyser Programme (ETAP)
software. The simulation revealed issues
with the substation's earthing system,
including broken and vandalized pits and
insufficient support. Measures were taken
to reduce the soil resistivity of the affected
pits, but further maintenance and
rebuilding of the earthing system are
recommended
to
ensure
optimal
performance and reliability of the
substation. Additionally, the simulation
results showed that the touch voltage, step
voltage, and mesh voltage of the substation
met the desired values. The earth
resistance of Pits 1, 2, and 3, however,
were discovered to have exceeded the
permissible values having read 2.63, 1.25,
and 1.16 respectively. As a result, each of
the pits was treated with ashes, salt, and
water, which resulted in a reduction in soil
resistivity of 70%. Additionally, it was
discovered that the substation has a fault
duration of 0.5 seconds, a fault current of
13785 amps, a rated ambient temperature
of 40 volts, a current division factor of 0.6,
and more, a grid short circuit current of 3
kA, a maximum permissible temperature
of 1084 volts, and a temperature of the
thermal coefficient of resistivity at zero
volts. The substation is safe and within the
permissible safe limits because the ground
potential rise (GPR) was measured at
2098.7 volts, which is lower than the
allowable limits. It is important to continue
monitoring and maintaining the earthing
system and the soil resistivity of the
substation to ensure optimal performance
and reliability of the substation over time.
Also, the earthing systems of pits 4 and 5
need to be urgently rebuilt.
Journal of Recent Trends in Electrical Power System
Volume 6 Issue 3
DOI: https://doi.org/10.5281/zenodo.10043497
2.
3.
4.
5.
6.
7.
8.
9.
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Cite as :
Hachimenum Amadi, Peter Nwauju, &
Dikio
Idoniboyeobu.
(2023).
Enhancement of the Grounding System of
132/33 kV Sub-transmission Station via
an ETAP-Based Approach. Journal of
Recent Trends in Electrical Power
System,
6(3),
27–37.
https://doi.org/10.5281/zenodo.10043497
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