TELKOMNIKA, Vol.15, No.4, December 2017, pp. 1530~1539
ISSN: 1693-6930, accredited A by DIKTI, Decree No: 58/DIKTI/Kep/2013
DOI: 10.12928/TELKOMNIKA.v15i4.7231
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New Waste Material to Enhance the Performance of
Grounding System
Nazatul Shiema Moh Nazar*, Suresh Thanakodi, Hazuwan Muhammad
Department of Electrical and Electronic Engineering, Faculty of Engineering,
National Defence University of Malaysia, 57000 Kuala Lumpur, Malaysia
*Corresponding author, e-mail: nazatul.shima@upnm.edu.my
Abstract
This paper presents the new waste material to enhance the grounding system application by
using Rice Straw Ashes as backfill to reduce the grounding resistance of the grounding system. Due to the
importance of the grounding system, this paper discussed the effectiveness of the grounding system after
using the additive material. The additive material that used are rice straw ash and bagasse ash. The
technique that used in this paper is a vertical type because more economical to install. From the result, it
was found that depth of electrode and soil treatment has an impact in reducing the grounding resistance.
In addition, Rice Straw ashes provide a better grounding performance comparable to Bagasse ashes.
Keywords: rice straw, bagasse ash, soil treatment
Copyright © 2017 Universitas Ahmad Dahlan. All rights reserved.
1. Introduction
All electrical system is equipped with grounding system. A good grounding system is
required for protection of buildings and installations against lightning. Grounding system also
provides a path to earth of enough current-carrying capacity so that protection of conductors
and equipment against fault to earth is provided. The grounding resistance need to be
effectively improved by getting a small grounding resistance to obtain a good grounding
system [1]. Besides that, safety of human and animal life by limiting touch and step voltages to
safe values. In addition, correct operation of the electricity supply network and to ensure good
power quality. The effective grounding system must provide a low impedance path to ground for
personnel and equipment protection and effective circuit relaying. Besides that, provide
correction allowance or correction resistance to various soil chemical to ensure continuous
performance during the life of the equipment being protected.
A grounding system refers to metallic wire of various geometric shapes and sizes,
acting as electrodes and buried in the soil. There are many types of electrode rod used as a
grounding system, but only two types are commonly used, vertical rod and horizontal rod. The
most elementary and most economical configuration of ground electrode is a vertical rod
electrode. This type of electrode is extremely effective for small installations. For horizontal rod
type, it is mainly used for large electrical installations and is usually buried in a shallow or
moderate depth [2].
Majority of grounding system uses salt (NaCl) as backfill with soil to reduce the
resistivity. But when rains, these salts will dissolve and loss the effectiveness. It was found that
NaCl addition successfully decrease the value of soil resistance, but the effect is temporary and
at the end of the monitoring period the value of resistivity has increased back to almost the
original resistivity value [3]. In order to maintain the low resistance, additional salt will be needed
and it will make the higher cost. So that, the alternative way is needed to overcome this
problem. From this problem, it consolidates the reason for Rice Straw ashes and Bagasse
ashes are selected to be as backfilled soil for the grounding system.
There are three objectives of this paper. First and foremost, to study the grounding
performance of local soil that use new waste addictive material. Second, to reduce the
grounding resistance of the grounding system. Lastly, to study the effectiveness of the
grounding system after using the addictive material. There are several scopes for this paper.
Firstly, the material used as grounding rod is red copper rod. Second, depth of electrode pushed
Received September 8, 2017; Revised November 12, 2017; Accepted November 27, 2017
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into ground depend on the length of the rod. The depth is 0.6 meter and 1.1 meter. Third, a
technique that use is vertical type. Fourth, rice straw ash and bagasse ash use as backfill
material to obtain a low resistance reading.
2. Parameters to Improve the Grounding System
2.1. Purpose of Grounding System
There are five main important things for the circuit and system to be grounded [4]. First,
when lightning happened. Second, when line surges. Third, when accidental contact with higher
electric potential lines. Fourth, to stabilize the electric potential to ground during normal
operations. Fifth, to expedite the overcurrent device operation in case of ground fault on a
solidly grounded system. The stranded conductor of a grounded system produces a lowresistance path for error-current through the overcurrent protective device to determine the
length of time a fault exits. It is important to plan to help the overcurrent protection device to
operate as soon as possible and keep the electricity as clean as possible [4]. There are three
reasons to keep the impedance in low value [5]. First, to minimize the voltage to ground.
Second, to smooth the operation of the circuit overcurrent protective devices. Third, drain
leakage, static, and unwanted noise-making currents to ground.
The proper installation of effective grounding works to establish protection for the
individual from voltage and current. With grounding, the voltage is eliminated. Then there is
nothing to drive the current through the body and the lower apposition path allows the current to
flow through something other than the physical structure [5]. In a script entitled “Grounding and
Bonding” that brought out by T. Condition as wiring regulations, it explained the meaning of
grounding which is the system that connects the general pile of land with the exposedconductive-parts of an installation via the conductors, the main grounding terminal (MET) and
the circuit conductor [6].
It also stated the purpose of source grounding. The purpose is to safeguard the security
of the supply network by preventing the potential of the lives conductors (with respect to the
earth) rising to a value consequential loss of supply. Other than that, purpose of electrical
equipment grounding also available in this book. It submitted that the connection of all exposed
conductive-parts of the facility to the intend means of grounding, and is always used when
protection against direct contact is by automatic disconnection of supply and earth equipotential
bonding. Besides that, the aim of such grounding is to facilitate the automatic functioning of the
protective devices for protection against electric shock and earth fault protection, hence that the
supply to the faulty circuit is disconnected immediately [6].
2.2. General Practical Ground Electrodes
The word "ground" is determined as a directing connection by which a circuit or gear is
identified with the earth. The connection is utilized to assemble and keep up as nearly as would
be prudent the capability of the ground on the circuit or equipment connected with it. A "ground"
comprises of a grounding conductor, a holding connector, its grounding electrode, and the soil
in contact with the terminal.
A grounding system refers to metallic wire of various geometric shapes and sizes,
acting as electrodes and buried in the soil. The vertical rod, horizontal electrode, ring electrode
and the grounding grid are four commonly used grounding electrodes as illustrated in Figure 1.
The most elementary and most economical configuration of ground electrode is a vertical rod
electrode. This type of electrode is extremely effective for small installations. It is more effective
when the seat layer of soil penetrated has lower impedance. Actually, if using a single stick,
generally do not reduce the resistance, so it is necessary to add a number of rods connected in
parallel [3].
The horizontal ground is mainly used for large electrical installations and is usually
buried in a shallow or moderate depth. The ring electrode is an instance of the horizontal
grounding grid and is now and again utilized as fringe ground conductors around structures like
wind turbines. In order to find even lower ground resistance, the horizontal ground grid can be
augmented with vertical poles, which are normally inserted at the fringe of the grounding
grid [3].
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Figure 1. Types of Grounding Resistance System of Transmission Tower [3]
2.2.1. Vertical Ground Electrodes
The vertical ground electrodes are the most usual type of electrodes in grounding
systems and usually the most economical to install. The long vertical electrodes can be used to
reach a low ground resistance in high resistivity soil and are driven to a few meter depth when
soil conditions allow. A series of high impulse current tests were held on four vertical ground
electrodes in different soils (shale, mud, crushed rock, sand) by Bellaschi. The current range
was from 2 kA to 8 kA and rise times varied from 6µs to 13µs. Again, the impulse resistance
was obtained as the ratio of peak voltage to peak current and, in agreement with previous work,
a fall of impulse resistance with increase of current was observed [7].
The impulse resistance dropped below the low frequency resistance, and this
characteristic was attributed to the soils electrical breakdown. It was confirmed that the size,
shape and the system of the ground electrode were factors contributing to the grounding
characteristics. The impulse resistance was determined for both plus and negative polarities;
the divergence was found to be really low. Deeply buried type or shaft type grounding can be
used when more profound underground soil resistivity is lower. The resistance can be lower by
getting an advantage of nearby natural grounding or the groundwater level is high and wet [7].
Figure 2 shows the vertical ground electrode grounding system.
Figure 2. Vertical Ground Electrode Grounding System
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2.2.2. Horizontal Ground Electrodes
Horizontal ground electrodes can be used to reduce the ground resistance of a
substation or a tower base footing. The horizontal ground electrode applied to tower lines may
be continuous or non-continuous and lay between towers and parallel to the line conductors.
Alternatively, conductors may be placed perpendicular to the transmission line and enhanced
arrangements using 4 points, 6 points or 8 points star can be used [2]. Geri and Garbagnati
conducted field trials on a horizontal steel ground electrode to investigate its impulse response.
Impulse currents with magnitudes from 5 to 26 kA and a rise time of 2.5 μs were injected into
the 5m long electrode. The impulse resistance was observed to decrease as the current peak
increased, and this reduction was attributed to the non-linear ionization phenomenon on the soil.
This technique can be connected when there is moderately great even horizontal
position and soil conditions close to the tower. Even horizontal mode has minimal effort on the
grounds that simple to introduce it. It cannot cut down the power frequency grounding
resistance, but also effectively diminishes adequate resistance while the expansion is not far [2].
Figure 3 shows the horizontal ground electrode grounding system.
Figure 3. Horizontal Ground Electrode Grounding System
2.3. Soil Resistivity
Soil resistivity plays a significant role when defining the intent of the grounding system
for new installations of transmission cable to meet ground resistance requirements. Preferably a
location with the lowest possible resistance is the best position to make a transmission tower.
The soil resistivity relies on moisture content, temperature, and soil composition. The resistivity
of the soil will change geographically and at different soil depths because the soil is seldom
consistent. Moisture content changes occasionally, differs as indicated by the way of the sub
layers of earth [8,9].
It is advised that the ground rods be placed as deep as possible into the earth
because soil and water are more stable at deeper stratum, at the water table if possible. Ground
rods also should be founded where there is a stable temperature, as example below the freeze
outline. For a grounding system to be efficient, it should be designed to resist the toughest
possible clime [1]. The soil resistivity is differing by its location. The soil at flat area usually has a
lower soil resistivity compare to the hill area. This is because the characteristic of hill area that
have stony soil and rock. Table 1 shows the soil resistivity on different type of soil.
Table 1. Soil Resistivity on Different Type of Soil
Soil
Surface soil and loam
Clay
Sand and gravel
Surface limestone
Shales
Sandstone
Granites and basalts
Decomposed gneisses
Slates
Resistivity(ohm-cm)
100-5000
200-10000
5000-100000
10000-1000000
500-10000
2000-200000
100000
5000-50000
1000-10000
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2.4. Backfill for Grounding
Backfill material is often used where grounding conditions are poor. The backfill was
prepared by mixing salt and local soil or by saturating the soil backfill with a salt-water solution.
Backfill other than soil was also used because soil is not always easily recovered from some
drilled or blasted holes and because unfrozen material is difficult to find during the winter.
Absorbent paper saturated with a salt solution and compacted in the hole around the electrode
was evaluated as a soil substitute in several installations.
2.5. Rice Straw Ash as Backfill Material
Rice straw is the waste products of the operation to obtain rice apart from rice grains.
Ashes of rice straw can be obtained from the combustion process. There are two types of rice
straw ash, which can be obtained from the stubble burning activities that is white ashes (carbonfree) and black ashes. The black ashes are in black color. They still have unburned carbon
compare to the white carbon that completely burn its carbon. The black carbon is denser, while
the white carbon is lighter. Ashes in general, have low resistivity significantly.
Rice straws have about 15% ash after burning, thus for 1000kg of rice straw being
burned, 150kg ash is produced and contain about 82% of silica. Because of the high silica in the
rice straw ashes it made the rice straw is one of the hydrophilic polymer that are easy to absorb
water [10]. While the resistance of the hydrophilic polymer will make the ashes to reduce the
amount of water being absorbed. So to take the ashes to absorb more water, the high quantity
of ashes needs to be applied. Figure 4 shows the burning process of rice straw ashes and
Figure 5 shows the sample of rice straw ashes.
Figure 4. Burning Process of Rice Straw Ashes
Figure 5. Sample of Rice Straw Ashes
2.6. Bagasse Ash as Backfill Material
The sugarcane bagasse consists of approximately 50% of cellulose, 25% of
hemicellulose and 25% of lignin. Each ton of sugarcane generates approximately 26% of
bagasse (at a moisture content of 50%) and 0.62% of residual ash. The residue after
combustion presents a chemical composition dominates by silicon dioxide (SiO2). Bagasse ash
mainly contains aluminum ion and silica [11]. Figure 6 shows the bagasse ash sample.
Figure 6. Sample of Bagasse Ash
3. Methodology
3.1. Selection Technique to Improve Grounding System
TNB’s transmission tower specification currently states that the tower footing resistance
of the 132kV and 275kV transmission towers has to be lower than 10Ω, while for 500kV
transmission towers the tower footing resistance has to be below 5Ω [9]. Those values were
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chosen because it is effective and low cost. After the selected techniques were applied, the
reading of the grounding resistance was taken and compared.
3.1.1. Increase the depth of the electrode rod
One very efficient way of lowering the ground resistance has increased the depth of the
ground electrode. In this technique, electrode rod is pushed deeper into the soil. The deeper the
electrode pushes into the soil, the lower the grounding resistance. The spacing of additional
rods needs to be at least equal to the depth of the driven rod so that the additional electrodes
will be effective [7].
3.1.2. A Soil treatment
Some other style to lower the earth resistivity is to handle the soil with a salt, such as
copper sulfate, magnesium sulfate, or sodium chloride. Combined with moisture, the salts leach
into the soil to reduce earth resistivity. In this paper, the local soil combined with salt, 2 kg of rice
straw ash and 2 kg of bagasse ash. Figure 7 shows the methods for the soil treatment.
Figure 7. Salt is put around the electrode rod
3.2. Conducting Testing
In order to achieve the objectives of this paper, the electrode rod will be planted into the
ground near the transmission tower. The electrode rod pushed to a depth of 0.2 meter, 0.4
meter, 0.6 meter, 0.8 meter, 1.0 meter and 1.2 meter into the ground. This experiment runs for
several days. Grounding resistance for each electrode rod was taken. Then the data were
analyzed and compared to validate the effect of the technique that chosen.
3.3. Testing Procedures
i. The selector switches in OFF position; the instrument was connected as shown in Figure 8.
Potential stakes and current stakes are driven into the earth, forming a straight line with the
test electrode.
Figure 8. Connection of electrode under test and stake
ii. The length of potential stake to electrode under test is at least 60% of the length of the
current stake to electrode under test. In this testing, length of potential stake is 3.6 meter
and length of current stake is 6 meter.
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iii. The selector switch is set to the 3 points resistance measurement marked “3p”.
iv. The desired voltage was selected using 50 volts.
v. The TEST button was pressed and released. By pressing and holding the TEST button, the
resistance measurement will be continually updated and displayed.
vi. In a short period, a resistance will be displayed in ohm and recorded in the table. The
readings were taken three times and were averaged.
vii. These readings are taken to get all the data.
4. Results
4.1. Result: Depth of Electrode Rod
As shown in Figure 9, it clearly shows that 1.2 meter depth has the lowest grounding
resistance. This result shows that the grounding resistance is proportional to the depth of the
electrode rod seen the deeper electrode rod planted into ground, the lower the value of
grounding resistance obtain. The lower resistance is needed so that lightning strikes or fault
current can discharge to the ground as fast as possible.
From the data taken, the grounding resistance can reduce up to 59% for a difference of
1.0 meter depth. The deeper electrode can reduce grounding resistance because the longer
electrode rod has a larger area to discharge fault or lightning strike to the ground. When the
electrode rod has larger area, it can quickly discharge the fault or lightning strike in a short time.
Therefore, the depth of the electrode rod can be one of the techniques to reduce the grounding
resistance of the transmission line tower. The deeper the electrode rod put in the ground, the
lower its grounding resistance.
Figure 9. Resistance of Local Soil (kΩ) versus Depth of Rod (m)
4.2. Result: Effect of Soil Treatment
Figure 10 to Figure 15 shows the resistance of soil treatment versus depth of rod.
However, the lowest grounding resistance is 0.074 kΩ or 0.000074 Ω as shown in Figure 13. It
shows that the electrode rod with (bamboo salt + rice straw ash) addition that represented by
Figure 13 has lower grounding resistance compare to the others. Due to salts are added around
the electrode rod, it will leach and react with the ground. The salt will migrate its charged ion to
the electrode rod from the copper electrode rod has the ability to attract charged particles and
reduce the soil resistivity. When the soil resistivity is low, there is easy to discharge the fault
compare to ground that have high soil resistivity.
This testing was made not to put salt into the all the transmission tower, but to show the
difference in soil resistivity can affect the grounding resistance. Usually, the higher place like hill
has a higher soil resistivity. This is because the higher place has stony soil, loamy soil and rock.
It means if the transmission tower is set up there, it will have a poor grounding system.
Preferably a location with the lowest possible resistance is the best position to make a
transmission tower. Hence the need to move the transmission tower to the suitable location for
grounding spot increase in the overall cost of installation because it will far away from the
facility. Therefore, soil treatment can use as a solution to this problem. Although the testing to
reduce the grounding resistance not according to the requirements of TNB which is below 10Ω,
but it can be concluded that the chosen technique can improve the grounding resistance of the
transmission tower by reducing the grounding resistance.
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Figure 10. Resistance of Soil Treatment (Himalayan Pink Salt) (kΩ) versus Depth of Rod (m)
Figure 11. Resistance of Soil Treatment (Bamboo Salt) (kΩ) versus Depth of Rod (m)
Figure 12. Resistance of Soil Treatment (Himalayan Pink Salt + Rice Straw Ash) (kΩ)
versus Depth of Rod (m)
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Figure 13. Resistance of Soil Treatment (Bamboo Salt + Rice Straw Ash) (kΩ)
versus Depth of Rod (m)
Figure 14. Resistance of Soil Treatment (Himalayan Pink Salt + Bagasse Ash) (kΩ)
versus Depth of Rod (m)
Figure 15. Resistance of Soil Treatment (Bamboo Salt + Bagasse Ash) (kΩ)
versus Depth of Rod (m)
5. Conclusion
There are two techniques can be used to reduce the grounding resistance which is
increasing the depth of the electrode rod and the soil treatment by using rice straw ashes and
bagasse ashes as backfill material. Both techniques are capable to reduce the grounding
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resistance. However, this testing cannot reach the TNB’s transmission tower specification. TNB
regulates that for the 132kV and 275kV transmission towers, the grounding resistance has to be
lower than 10Ω. The research location that was held in the hill area makes it difficult to get the
rounding resistance below 10Ω. As a conclusion, it is important to have a better grounding
system. In order to make sure the grounding system is in good condition, it is compulsory to
retain a low grounding resistance. Therefore, it can prevent lightning interface of transmission
line and to assure security operation of the power system.
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