Comparison Study of Usage as Grounding Electrode between Galvanized
Iron and Copper with and without Earth Additive Filler
F. Mahtar, A.Ramli, W.R.Wan Abdullah, M.N. Isa
Telekom Research And Development Sendirian Berhad. Idea Tower, UPM-MTDC, Technology Incubation Center One, Lebuh Silikon, 43400,
Serdang, Selangor Darul Ehsan.
{fakhrul, annuar, wanrazli, fallah} @tmrnd.com.my
Abstract – With increasing price-hike for copper and
its vulnerability to theft, there is some concern to
telecommunications, utility company and building
contractors to find an alternative material to copper as
a grounding network. It has been known that
galvanized iron is one type of steel that has been used
extensively as a strengthener in pole construction,
especially in Malaysia. Because of its electrical
characteristics and reasonably low price, galvanized
iron also can be considered as an alternative to copper
as a grounding material. In this paper, evaluation is
being done in order to verify the performance of
stranded galvanized iron as grounding network. Mock
up systems with both copper tape and galvanized iron
wires have been constructed in the same site, which
having 2 layer soil models based on soil resistivity
measurements which have been conducted and
simulated
by
using
Current
Distribution,
Electromagnetic Fields, Grounding and Soil Structure
Analysis (CDEGS) software by Safe Engineering
Services & Technologies Limited. The performance of
both copper tapes and galvanized iron wires has being
monitored for 6 months from the installation date. By
referring to the measured data, the performance of both
copper and galvanized irons can be viewed and
compared. The results prove that there is significant
effect of better usage of copper as grounding electrode
compared to galvanized iron, in terms of overall
grounding impedance of the systems, based on 25
weeks’ data, especially for grounding systems which
have been added with earth additive filler (EAF).
Keyword; Copper, galvanized Iron, grounding impedance,
CDEGS Software, Earth Additive Filler (EAF).
1. Introduction
The grounding electrode of an electrical
installation is the way into the earth for the electrons.
Therefore, installing a grounding electrode in the earth
means installing an electrical terminal to help the
electrons travel into earth [4]. Choosing suitable
conductors for the grounding grid is important not only
to provide satisfactory performance, but also to
maintain the quality of grounding system over the long
term [3]. In normal practice, a typical grounding
system will consist of horizontally buried conductors,
which usually use copper tape in rectangular form, as
in Telekom Malaysia case, 25mm X 3mm. As a fact,
copper is chosen ahead of other type of conductors and
materials because of its ability to conduct current due
to its higher conductivity level and lower permeability
level, thus making it is easier to discharge current to
earth in case of grounding systems. Another advantage
of copper is that the resistance against corrosion,
where copper is less subjected to corrosion because of
its neutral characteristics, compared to other type of
conductors. Most of the time, grounding systems in
Malaysia use copper as grounding conductors, whether
in telecommunications industry, as well as in power
utility section.
Meanwhile, in some other Asian countries, such
as China, there are a lot of grounding systems still use
steel as conductors for grounding systems [1]. The
major factor of using steel as grounding conductors is
that the price of steel is much lower compared to
copper. Besides, steel conductors are also having less
risk to theft due to cheaper price. In fact, in China,
most of 1970’s and 1980’s grounding grids are made
of steel [1]. But, the fact is as steel bear a much higher
permeability and lower conductivity than copper,
making it less preferable compared to copper for
grounding
purposes.
This
indifference
of
characteristics is likely to cause some issues,
particularly for electronics equipments’ operations
inside the telecommunications outdoor cabinets or
substations owing to there are significant potential
differences between different parts of the systems,
particularly for the large systems.
Besides, steel conductors are well known for its
vulnerability for corrosion, compared to copper.
Corrosion of steel conductors can result in an impaired
grounding system that could cause serious problems,
especially when fault occurred. Indeed, in China since
the end of 1980’s, many serious power failure
incidents have been reported and it is found that
inadequate grounding is one of the important causes in
most accidents [1].
The focus of this paper is to analyze the
performance of grounding systems made of galvanized
iron and copper, in the same site which having a
resemblance of soil resistivity model and value, plus
the effect of earth additive filler that has been utilized
around the mock-up systems. Based on field
measurement data which have been monitored
consistently for 6 months, the performances for each
grounding system are compared and analyzed. Soil
resistivity measurements as well as soil simulation by
means of CDEGS software are also presented in this
paper.
2. Soil Resistivity Measurement and
Simulation
Soil resistivity measurement and interpretation are
an essential task for an accurate grounding analysis
[3]. The soil resistivity data are the most important
data needed in order for a grounding system to be
designed and constructed properly. The importance of
the data is so crucial that the soil resistivity
measurement data must be done before any grounding
networks are constructed. This is to ensure that the soil
resistivity data collected are of true soil resistivity
values without any influence from any buried metallic
structures. For this paper, the soil resistivity data are
obtained by using a 4-pole measurement method based
on Wenner Array method. The data collected from the
soil resistivity measurement are of apparent resistance
as tabulated in Table 1.
Table 1: Soil Resistivity Data at the mock-up test
site in Shah Alam, Malaysia
Spike Spacing
(meter)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Apparent
Resistance (Ohm)
12.78
7.35
4.49
2.48
1.49
0.9
0.55
0.4
0.31
0.24
0.2
0.2
0.18
0.17
0.15
Based on the measurement data, then the
simulation is conducted by using CDEGS Software, as
originally designed by Safe Engineering Services &
Technologies Limited, Canada. This software is able to
model the multilayered soil model by using the
standard soil resistivity data. In detail, the RESAP
module has been used to model and simulate the soil
layer. The simulation results are shown in Table 2.
Table 2: Layered soil model from RESAP Module
Layer
Number
Resistivity
(Ohm-meter)
Thickness
(meter)
1
2
3
infinite
98.91554
11.87216
infinite
2.829872
infinite
In Figure 1, the module shows the Soil Resistivity
Curve which interpret the soil model as in Table 2.
Figure 1: Soil Resistivity Curve
From the soil resistivity data and curve which
have been simulated by CDEGS, it shows that the soil
model at the mock-up test site in Shah Alam has
basically 2 layered soils. It is generally a Hi-Lo model
where the upper layer is having high resistivity value
compared to the 2nd layer. With this soil model, along
with its respective thickness, future grounding systems
that will be constructed in the site can be maximized in
terms of lowering the grounding impedance so that the
systems will not be under design or over design.
3. Mock-up Systems Constructions
The mock-up systems which have been built are
consisting of 4 holes which have been constructed to
monitor the grounding impedance for 4 different
scenarios, which are as the followings:
1.
2.
3.
4.
Stranded galvanized iron.
Stranded galvanized iron with addition of
EAF.
Copper tape.
Copper tape with addition of EAF.
The illustrations for the mock up systems are
shown in Figure 2.
Figure 2: Trenches with stranded galvanized irons
and copper tapes
The mock up systems which have been built
and been monitored for 6 months with a constant
time frame of measurement in order to see if there
are any changes of grounding impedance values
from time to time.
Figure 2 shows that there are 4 separate
trenches constructed. The grounding impedance
measurement is conducted to all trenches and the
data are recorded. For trench 2 and trench 4, there
are different from the rests as these trenches are
added with EAF, which is carbon based powder
type filler which is marketed worldwide. The
usage of this material is to reduce the grounding
impedance value of the systems. So, for the
measured data, it is expected that the grounding
impedance values of these trenches will be lower
than the same galvanized iron and copper tape
without EAF.
The specification for galvanized iron and
copper tape which has been applied here is shown
in Table 3.
Table 3: Galvanized Iron and Copper tape
specifications
Type of earth
electrode
Total length
(m)
Size or
dimension
GI wire
5.0
Copper tape
(or copper
strip)
5.0
Diameter:
7.62mm or
2
35mm
square with
7/2.53 strand
25mm (w) x
3mm (h)
4. Results and Observations
The measurement data for the grounding
impedance have been done by using a 3-pole earth
tester. The measurement is carried out by using a
modern earth/ground tester with current probe
positioned 60 meter from the grounding tape and
the impedance value is calculated by using Tagg
Slope technique. This is because when the data are
retrieved, there is no clear flattening on the
resistivity versus spike spacing graph. So, the
determination of the grounding impedance has to
be determined by using Tagg Slope technique.
The resistance readings are done at 20%, 40% and
40% from the length of current spike, which is 60
meter. So, the resistance has been measured at the
respective 12 meter, 24 meter and 36 meter for
potential spike spacing. Then, the calculation of
slope coefficient (µ) by using 3 resistance data at
20%, 40% and 60% is based on the following
formula:
µ = (R60% - R40%)
(R40% - R20%)
After µ value has been determined, then the
corresponding ratio of potential spike over current
spike spacing will be determined and from the
table of Tagg Slope technique Coefficient value,
in which it will determine at what value of
potential spike spacing distance the grounding
resistance value suppose to be. After that, the
measurement at the determined spacing will be
conducted and the resistance at that particular
potential spacing will be used as the true
grounding impedance value for the respective
grounding network. The measured data from the
mock-up test site in Shah Alam, Malaysia are
shown in Table 4 and Figure 3.
Table 4: Grounding Impedance data for 25
weeks
better in terms of conductivity of current compared to
galvanized iron.
4.1
Grounding
CDEGS Simulation
Figure 3: Measured Ground Impedance Data
The measured data reveal that there are decreasing
values of all trenches in terms of grounding impedance
value from week 1 until week 25. For trenches with
addition of EAF, the values seem to be consistent starting
with values from week 20 and beyond. The reductions of
grounding impedance values between the same
conductor trenches with EAF and without EAF are
41.9% % for galvanized iron and 42.4 % for copper
tapes, based on the 25th week data. The corresponding
data for every fortnight for the respective conductors are
outlined in Table 5.
Table 5: The percentage of reduction for trenches
with EAF taken by weekly basis
Impedance
Result
by
In addition to field measurement, the simulation
by using CDGES software, particularly MALZ module
that can model the usage of EAF in grounding network,
with all main characteristics such as permeability and
resistivity of the material are defined in the module. As
for this case, the usage of EAF is modeled as a single fat
plate conductor, in which the dimension of the effective
radius for the plate is calculated by equivalent cylindrical
conductors dimension as attached by Safe Engineering
and Technologies Limited. From the simulated result, the
grounding impedance for galvanized iron and copper
tape without the addition of EAF are 23.16 Ohm and
20.74 Ohm, respectively, in which yield the difference of
10.44% between each other. Meanwhile, the differences
between field measurement and simulated values are
14.50% for galvanized iron and 14.41% for copper tape
in week 25.
For trenches which have been added with EAF,
the simulated data yield the results in which the
galvanized iron trench and copper tape trench give 10.18
Ohm and 10.14 Ohm, respectively which make the
difference between these values is 0.39 %. Meanwhile,
the difference between the field measurement value with
that of the simulated value is 11.47 % for galvanized iron
and 0.78% for copper tape in week 25.
5. Discussions
The difference of grounding impedance value for
copper tape and stranded galvanized iron is 10.45% for
systems without EAF. Meanwhile, the difference for
trenches with addition of EAF is 11.13 %, much higher
compared to trenches without EAF.
There is a
significant difference for trenches with EAF for both
stranded galvanized iron and copper tapes, as well as
trenches without the addition of EAF. This is most likely
caused by surface contact between the grounding
electrode and the soil, which is so inferior, compared to
those trenches with addition of EAF, where the surface
contact between the horizontal parts and the soil is much
better because of bigger surface area with addition of
low-resistivity material in EAF. Thus, the current
discharge to earth disperses into ground much better. For
systems with EAF, the impedance value difference are
much bigger, with 11.13%, where the concern here is
that the surface contact between the EAF and soil, but
more likely to be decided by the characteristics of the
conductors itself, where obviously the copper will be
Overall, it can be seen that there is a discrepancy
between the field measurement data and simulated data.
This discrepancy is most likely caused by the physical
condition of the site itself, where it can be seen that most
of the time when the measurement is carried out, the
surrounding condition is so wet. The wet conditions tend
to give lower reading of grounding impedance values.
The results obtained from the CDEGS simulation
seem to perform higher reading than the field
measurement results for trenches without EAF.
Meanwhile, for systems with addition of EAF, the
CDEGS simulation data demonstrate slightly lower than
the measured data. The difference between these values
is caused by the assumption made by CDEGS in which
for trenches with EAF, the horizontal part of the
conductors is modeled as a big horizontal plate with the
respective conductors’ characteristics, in this case the
galvanized iron and copper. The assumption made in the
CDEGS software will improve the surface contact
between conductors and soil, which will eventually
increase the current dissipation into ground, thus
lowering the impedance value of the conductors.
Meanwhile, for trenches without EAF, the contact
between conductors and soil are assumed as a constant
value in CDEGS, without any interaction with water and
moisture inside soil, which originated from the rain and
other moisture sources contained in the soil.
Based on 25 weeks’ data, the measurement data
yield the results that the usage of EAF can lower the
grounding impedance data, compared to the identical
type of conductors without having the EAF. It shows that
the trenches without EAF have their impedance values
drop, starting from week 10 until week 25. This is most
likely to be caused by the effect of rain and also the
effect from the adjacent trenches which equipped with
EAF, in which some particles from EAF from the
adjacent trenches help to some extent lower the
impedance values to the non-EAF trenches up to 10%15% from the date of installation. Meanwhile, for
trenches with EAF, the impedance values seem to be
more stable, starting from week 4.
Furthermore, the impedance values for trenches
with EAF take less time to stabilize compared to nonEAF trenches for example trenches 2 and 4 almost
immediately settle to constant value in week 2, whereas
trenches 1 and 3 take longer time to stabilize. This is the
evidence that the usage of the EAF help to some extent
shorten the impedance value stabilization, disregard of
type of conductors being used. The data trends between
CDEGS simulation and field measurement show a
resemblance, despite the difference in terms of values
recorded for the respective trenches and weeks.
6. Conclusions
In conclusion, the results show that the
performances of galvanized iron against copper tape in
the same multilayered soil seem to be having a
significant different, based on 25 weeks data measured at
the test site. The radius of the galvanized iron also plays
an important role as the difference between the areas of
these conductors is almost half. Therefore, using the
bigger galvanized iron conductors will bring down the
impedance value of the systems, as more current can pass
through the conductors. This is because the conductivity
of copper is better than galvanized iron.
It can be seen from the data that the impedance
data for trenches with EAF seem to be more stable, while
the trenches without EAF seem to drop and fluctuate
until they come to the 25th week where the data are less
fluctuating. The trenches with EAF are also having some
effects to their adjacent trenches where the impedance
values of the latter drop from week to week. Further field
measurement needed to ensure the impedance data will
finally come to a constant value, thus further study and
measurement needed on the site.
Extended studies needed especially to observe the
performance for both types of ground conductors when
come to corrosion effect, as the mock-up test site in Shah
Alam, Malaysia is situated in an industrial area where
there is a lot of gas emission from the industries nearby
which lead to acid rain which can speed up the corrosion
effect on metal. The possibility of increasing impedance
data for both systems with and without EAF will be
investigated within a period of 3 – 5 years. This will
ensure the effectiveness of EAF against the corrosion
effect to both systems.
References
[1] Y. Li, F.P. Dawalibi, J. Ma,Y. Yang, C.Y. Li,
W. Xu and J.S. Zhang, “Analysis of Steel
Grounding : A Practical Case Study” IEEE
Journal Paper.
[2] Yexu Li, Jinxi Ma, Farid Paul Dawalibi and
Jinsong Zhang, “Power Grounding Safety: Copper
Grounding Systems Vs Steel Grounding Systems”
IEEE Journal Paper.
[3] J. Ma and F.P. Dawalibi, “Study of Influence of
Buried Metallic Structures on Soil Resistivity
Measurements” IEEE Journal Paper.
[4] R. P. O’Riley, Electrical Grounding, Delmar
Publishers Inc, New York, USA, 1993