Reduction of Earth Resistance Using Agricultural Waste Materials as Back-fill.PDF

7/27/2019 Reduction of Earth Resistance Using Agricultural Waste Materials as Back-fill.PDF

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PERFORMANCE OF AGRICUTURAL WASTE AND OTHER BACKFILL

MATERIALS FOR REDUCTION OF EARTH RESISTANCE

B. S. Dahiru1, W. F. Wan Ahmad

1, J. Jasni

1, and W. M. N. Wan Daud

2

1. Department of Electrical and Electronic Engineering

Faculty of Engineering

Universiti Putra Malaysia

43400 UPM Serdang

Selangor, Malaysia.

2. Department of Crop Science

Faculty of Agriculture

Universiti Putra Malaysia

43400 UPM Serdang

Selangor, Malaysia.


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ABSTRACT

Many earthing techniques have been employed to achieve low resistance earthing but

somehow it is difficult due to the variation of soil characteristics from one point to the

other. The use of industrial and agricultural wastes as backfill materials for reducing earth

resistance has received recognition recently where in this study, agricultural waste such

as palm kernel fibre, kenaf fibre, paddy dust and clay based materials such as bentonite

and Sungai Besar Marine Clay were used as backfill material filled in five holes with

0.13m diameter and 1.5m deep. Five copper electrodes of 0.013m diameter and 1.5m

long were driven at the centre of each hole allowing 0.1m above grade for clamping of

earth resistance measuring instrument. Another earthing installation was made by driving

a copper electrode directly into the soil to serve as reference installation. Earthing

installations were separated at 3m intervals to avoid overlapping of sphere of influence

from adjacent installations. Plastic earth chambers were placed on each earthing

installation to serve as inspection boxes. Earth resistance measurement was conducted on

daily basis for one year using an Earth Tester. Results indicated that after one year of

installation, the earth resistances have averagely reduced by 53.85%, 41.56%, 33.54%,

20.14% and 15.2%, respectively for bentonite, palm kernel fibre, Sungai Besar Marine

Clay, kenaf fibre and paddy dust when compared to the reference earthing installation.


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1.0 INTRODUCTION

Earthing has been defined as the provision of a permanent and continuous conductive

path to the earth that has sufficient capacity to carry any fault current liable to be imposed

upon it, has sufficient low impedance to limit the voltage rise above ground potential, and

that facilitates the operation of protective devices in the circuit [1]. Meliopoulous [2]

stated that, a structure is called earthed if it is electrically connected to an earth-

embedded metallic structure, where the earth embedded structure is called the earthing

system and provide a conducting path of electricity to earth. The main purpose of

earthing is to maintain a reliable operation of power system and to provide protection to

personnel, equipment and the system itself during both normal and fault conditions.

Furthermore, earthing system will provide a safe path for the dissipation of fault currents,lightning strikes, static discharges, electromagnetic interference (EMI) signals to the earth

without disturbing anything in the middle [3]. Earthing is also required to provide signal

reference in telecommunication and data facilities.

The Institution of Electrical and Electronic Engineers (IEEE) Standard 142,

recommended soil treatment as a measure to improve earthing resistance in high

resistivity soils [4]. The British Standard, BS7430 on the other hand recommends

replacement of high resistivity soil with low resistivity soil or other material to improve

earthing resistance in high resistivity soils [5]. The use of industrial, agricultural or

biological wastes as backfill materials for reduction of earth resistance has been severally

reported in published literature.

Agricultural and industrial waste products have recently gained recognition in

many economic and technological applications ranging from biofuel to composites.

Initially, these products posed substantive environmental and ecological problems in

terms of disposal. However, recent advances in technology has led to what is called

conversion of liability into asset by utilizing the by products for useful purposes [6]. In

this study, agricultural by products such as palm kernel fibre (PKF), kenaf fibre, and

paddy dust in addition to bentonite and Sungai Besar Marine Clay (SBMC) were used as

backfill materials for reduction of earth resistance of earthing systems.


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Palm oil milling is a major industry in Malaysia which produces palm oil and

numerous by products such as palm kernel cake (PKC), palm oil sludge (POS), and PKF

[7]. PKF is used in one of the earthing installations presented in this work. PKF is

composed of 65% cellulose and 19% lignin which make it a good sorbent material like

other fibres [8]. Paddy dust (rice husk) is also an agricultural by product of the rice

milling factory which is also one of the major agricultural industries in Malaysia. It

constitutes about 20% of the weight of rice, 50% cellulose, 2530% lignin and 1520%

of silica producing 200kg of husk for every 1000kg of paddy milled [9]. Kenaf plant

(Hibiscus Cannabinus linn) is a hot season annual fibre crop which has been used for a

long time to produce twine, rope and sackcloth. Nowadays, there are several new

applications of kenaf fibre including paper products, building materials and absorbents

[10]. All the three agricultural waste products are fibrous in nature and are abundantly

available in Malaysia, and very cheap. Bentonite which is claimed to be the best agent for

reducing earth resistance [11] is commercially available and affordable, while SBMC is a

clay type material obtained from Sungai Besar, Selangor, Malaysia. It is composed of

2-8% sand, 46-60% silt and 33-52% clay, with chemical properties such as, pH of

7.2-7.5, organic matter content of 5-14%, carbonate 9-13%, CEC 25-75 meq/100g, and

mineralogy class of Lillite-Montmorillite [12].

2. BACKFILL MATERIALS

Application of backfill materials for reduction of earth resistance is based on earth

electrode enhancement or electrode encasement as referred to in [14-15, 18-19].

Increasing the diameter of a driven earth electrode reduces the earth resistance by a small

fraction only. It was reported in [13] that increasing the diameter of an earth electrode

from 12.5mm to 25mm has increased the weight of the electrode by 400%, increased its

cost by 400%, but reduced the earth resistance by 9.5% only. Hence, the idea of using

backfill materials in contact with the earth electrode is indirectly increasing the diameter

of the electrode with a cheaper alternative. It is desirable that backfill materials should

have low resistivity value, if possible lower than the soil at the installation site.


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Several works on electrode enhancement using both industrial and agricultural

wastes as backfill materials have been reported in literature. Gomes et al. [14] reported

the use of metal oxide powder, a waste product of steel industry, granite powder and cast

iron powder as backfill materials around a galvanized iron (GI) electrode. While

Chen et al. [15] conducted a study to determine the optimum quantity of earth resistance

reduction agent using granulated blast furnace slag as backfill material in a pit of 0.13m

diameter by 0.9m deep. The use of conductive cement as backfill material was also

reported in [16] as an arrangement having dual advantage of maintaining the earth

electrode moist and also preventing the electrode from being corroded. The earth

resistance was reported to have reduced by 50-90% when compared to the reference

electrode.

Furthermore, the earth electrode resistance could be reduced by replacing the soil

in the critical resistance area with a soil of lower resistivity as reported in [13]. The use of

biological wastes, such as mixture of cow waste and sand, chicken waste, saw dust, ashes

and garden soil as backfill materials was reported in [17]. The resistivities of the waste

materials were measured and results indicated that ashes had the lowest resistivity,

followed by chicken waste and cow waste. Kumarasinghe [18] reported that earth

resistance of a lightning protection system could be reduced by using bentonite and

agricultural waste materials such as coconut coir peat and rice paddy dust as backfill

materials. It was also reported in [19] that palm kernel oil cake (PKOC) could be used as

backfill material to reduce earth resistance.

3. MATERIALS AND METHOD

A resistivity box of 0.1m3dimension was constructed using Perspex glass with stainless

steel plates attached to the opposite faces of the box to serve as parallel plate terminals asshown in Figure 1. The capacitance of the box was measured and found to be 1.0832

pF/m using LCR meter as illustrated in Figure 2. Each backfill material was alternately

placed in the box and compacted, and then the resistance is measured using the LCR

meter where the typical arrangement is as shown in Figure 3. The dry resistivity of each

material was determined using equation (1) where is the resistivity in -m, R is the


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measured resistance in Ohms, A is the area of the stainless steel plates in metres square,

and L is the distance between the plates in metres, and the results are listed in Table 1,

while the resistivity of bentonite at 300% water content was reported as 2-5-m in [20].

Subsequently, an experiment consisting of six earthing installations was set up at

the Faculty of Engineering, Universiti Putra Malaysia, Serdang, Selangor, Malaysia. Five

holes with 0.13m diameter and 1.5m deep were drilled and each hole was filled with a

different kind of backfill material and compacted. Five copper electrodes of 0.013m

diameter and 1.5m long were then driven at the centre of the holes to a depth of 1.4m

allowing 0.1m above grade for clamping of earth resistance measuring instrument. The

sixth earthing installation was made by driving another copper electrode directly into the

soil to a depth of 1.4m to serve as the reference installation. All earthing installations

were separated 3m apart from adjacent installations to prevent overlapping of sphere of

influence. Plastic earth chambers were placed on all earthing installations to serve as

inspection boxes and also to fulfill the requirement of Malaysian Standard. An Earth

Tester was used to measure the earth resistance daily based on 3-point fall of potential

method and the performance of earthing installations is evaluated on monthly basis in

comparison with the reference installation using equation (2) where Rreduc denotes the

reduction in resistance, Rref denotes the resistance measured at the reference installation,

and Renhanc

is the resistance of earthing installations with enhancement materials.

LRA

(1)

%100..

.

ref

enhancref

reducR

RRR (2)

4. RESULTS AND DISCUSSION

Table 1 lists the measured resistance and calculated resistivity of the backfill materials

used in this study. Results indicate that SBMC recorded the lowest resistivity value

possibly owing to its smaller grain size when compared to the other backfill materials, i.e.

1.952k-m. The calculated resistivity values for Kenaf fibre, PKF and paddy dust are

2.881k-m, 5.330k-m and 6.054k-m, respectively. The high resistivity values


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obtained from the agricultural wastes may possibly be due their fibrous texture which

may contain air pores and also due to difficulty of being compacted.

Figures 8 to 19 demonstrate the measured earth resistances for all six earth

installations for a period of one year where the performance is presented on monthly

basis. Figure 8 illustrates the graph of measured earth resistances for the first month after

installation where results indicate that the resistances for all earthing installations were

initially high and unstable but gradually reduced after about three weeks. Typical

resistance readings were within the range of 20 to 30 for bentonite, SBMC and PKF

installations, while the resistances for kenaf fibre, paddy dust and reference installations

range from 40 to 55. Themeasured earth resistances for the second month are shown in

Figure 9 where it is observed that the resistance readings for bentonite, SBMC and PKF

installations were still within the range of 20 to 30 but yet not stable. Similarly, the

resistances for kenaf fibre, paddy dust installations remained within 40 to 55 range

although not stable. Note that the resistance of the reference installations was above 60

and recorded the highest value.

Figure 10 demonstrates the measured earth resistances for the 3rd

month where r

the resistances are generally low and stable with bentonite, SBMC and PKF installations

measured about 25, paddy dust and kenaf fibre installations recorded resistances of

about 35. However, resistances measured for reference installations are in the range of

40-50. The graph of measured earth resistance during the fourth month is as shown in

Figure 11 where resistance values are stable and previous values were maintained.

During the fifth month, it is observed from Figure 12 that resistances have

slightly increased where resistances measured for paddy dust and kenaf fibre installations

were almost above 44 and 40, respectively. Similarly, the resistances for PKF and

SBMC installations were measured as 26 and 30, respectively. Note that measured

resistances for bentonite installation were nearly stable at about 20. Figure 13 shows the

performance of earthing installations after six months. It is observed that the resistances

on all installations have slightly decreased where the resistance on the reference

installation was seen to vary and in the range of 40 and 50, while paddy dust and kenaf

fibre installations recorded resistances less than 40. In the same vein, the resistances for


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PKF and SBMC installations were about 25 while bentonite installation indicated a

stable resistance of about 20.

During the seventh month, the earth resistances of all earthing installations were

nearly maintained at their previous values but there were evidences of instability as

illustrated in Figure 14. The performance of earthing installations after 8 months is as

shown in Figure 15. It is observed that the resistances began to increase on day 221 and

continued steadily up to day 240 where the paddy dust installation indicated a resistance

value higher than the reference installation. Resistance readings for reference and kenaf

fibre installations were above 60, while SBMC recorded a resistance of nearly 40.

Measured resistances for PKF and bentonite installations are 38 and 29, respectively

. Figure 16 illustrates the measured earth resistances for the 9th

months. It is

observed from the graph that paddy dust and kenaf fibre installations recorded resistance

values well above the reference installation suggesting a poor performance from the two

backfill materials. Typical resistance values for paddy dust and kenaf fibre installations

were 130 and 102, respectively. The average resistance readings obtained on other

installations are 65, 60, 57 for reference, PKF and SBMC installations, respectively.

Note that bentonite installation measured averagely 30 during the same period. The

increase of earth resistance for all earthing installations may be related to a prolonged

period of drought which prevailed during the eighth and ninth months lasting for about

three consecutive weeks. Also, the results for the eighth and ninth months further indicate

the influence of moisture content on earth resistance. Although paddy dust and kenaf

fibre have moisture retaining characteristics, prolonged period of drought still had some

impact on their performance as backfill materials. Another possibility for the poor

performance of the two backfill materials after the seventh month may be due to

biodegradation of the materials which may create voids at the contact surface between the

earth electrode and the backfill material. This suggests that paddy dust and kenaf fibre

installations may require replenishment or maintenance after the fifth months to maintain

good performance.

Figure 17 shows the measured earth resistances after 10 months. It is observed

that the resistances on all earthing installations are high but have slightly decreased from

their previous values. Paddy dust installation recorded the highest resistance with 118


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followed by kenaf fibre and reference installations with 82 each. SBMC, PKF and

bentonite recorded resistances of 67, 59 and 39, respectivelyduring the 10th

month

of observation. The performance of the earthing installations after 11 months is illustrated

in Figure 18. It is observed that the resistances for all installations have decreased

drastically with the reference installation measuring averagely 50. Paddy dust, SBMC

and kenaf fibre installations recorded an average of 40 measured resistances. PKF

installation recorded an average of 32 and bentonite installation recorded an average of

24during the 11th

month of earth resistance measurements.

Performance of the earthing installations after one year is as illustrated in Figure

19 where it indicates that on average, the resistance values of the previous month for

most installations were maintained but not stable due to sharp variations caused by

degradation of the backfill materials resulting in formation of voids at the contact surface

between the earth electrode and the backfill materials, and also may possibly be due to

alternation between dry and wet soil conditions. The summary of measured earth

resistance readings for a period of one year is listed in Table 2. It indicates that the final

earth resistances achieved by installations with backfill materials were 38.10, 48.50

and 60 for PKF, kenaf fibre and paddy dust earthing systems, respectively. Similarly,

25.40 and 48.20 was obtained from bentonite and SBMC installations. The results

indicated that the earthing resistance measured on SBMC installation is higher than its

initial value on day 0. This may possibly be due to settlement of the SBMC in the hole

which may create voids thereby leaving the earth electrode bare.

The percentage reduction of earth resistance for backfilled earthing installations

compared to the reference installation for a period of one year is presented in Table 3.

Results in the first row indicate the percentage difference of earth resistance between the

reference installation and other installations on day 0. The numbers 1 to 12 in column 1

represents 12 months and while 365 days completes the duration to one year. It is

observed that PKF installation recorded an average of more than 40% reduction of earth

resistance for a period of 10 months but decreased to barely more than 30% thereafter.

This possibly suggests that the backfill material has undergone biodegradation and

requires maintenance. Another possible cause of poor performance of backfill materials


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after long periods of installation is the formation of voids at the contact surface between

the earth electrode and the backfill materials.

The results also reveal that the kenaf fibre installation recorded averagely about

30% reduction of earth resistance in the first five months after which its performance

declined. For instance, during the seventh month, the earth resistance of the kenaf fibre

installation was 0.39% more than the reference installation. This clearly suggests that in

order to maintain good performance, kenaf fibre installation should be maintained after

five months. Considering paddy dust installation, it is observed that the performance is

generally not consistent but a reduction of slightly above 30% was achieved in the first

five months. However, the performance declined to less than 20% during the sixth month.

Specifically during the eighth month, paddy dust installation recorded a resistance of

16.27% above the reference installation. Similarly, after the 12thmonth i.e. on day 365,

the resistance measured on paddy dust installation was 2.92% above the reference

installation. This also suggests that it needs maintenance after five months to ensure good

performance.

Bentonite installation recorded the highest percentage reduction of earth

resistance, and was also consistent where over 50% reduction was maintained throughout

the year. SBMC installation also performed fairly well for a period of seven months

recording a reduction of resistance of nearly 50% after which the performance declined to

barely 20%. This also suggests that the installation would require maintenance after

seven months to ensure good performance.

5.0 CONCLUSION

The performance of agricultural waste and clay based materials for reduction of earth

resistance was investigated using six earthing installations, 5 backfilled and 1 reference.

The study revealed that after 365 days, PKF, kenaf fibre, paddy dust, bentonite and

SBMC earthing installations recorded resistances of 38, 48, 60, 25.40, and

48.20, which are reduced by 41.56%, 20.14%, 15.2%, 53.85%, and 33.54%,

respectively when compared to the reference installation starting from day 0. It is

concluded from the results that bentonite installation is the best performed earthing


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installation followed by PKF and SBMC installations. Paddy dust installation is the least

performed earthing installation. Therefore, bentonite, PKF and SBMC are considered

suitable backfill materials for reduction of earth resistance. The use of backfill materials

for reduction of earth resistance is cost effective as the backfill materials are cheap and

available. Also, they are environmentally friendly, although they may require

maintenance after certain periods of time to replenish the materials to ensure good

performance. Bentonite installation may require maintenance after one year, whereas

SBMC, paddy dust and kenaf fibre installations would need to be maintained after 7 and

5 months, respectively.

Figure 1 Schematic diagram of resistivity box [21].


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Figure 2 Measurement of capacitance of

the resistivity box

LCR meterResistivity box

Figure 3 Typical measurement ofresistance of the backfill materials used

Paddy dust


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Figure 4 Layout for installation of earthing system

Fi ure 5 T ical hole drillin rocess

Hole drillingmachine

Flushing pump


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Figure 6 A typical 0.13m diameter and 1.5m

dee hole

Figure 7 Typical completed earthing installation

Earth electrode


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Figure 8 Graph of measured earth resistance after one month

Figure 9 Graph of measured earth resistance after 2 months



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.


Fi ure 15 Gra h of measured earth resistance after 8 months



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Figure 19 Graph of measured earth resistance after one year


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Table 1CALCULATED RESISTIVITY VALUES FOR VARIOUS BACKFILL MATERIALS

Backfill material Measured resistance (k) Calculated resistivity values (k-m)

PKF

Kenaf fibre

Paddy dust

SBMC

53.295

28.810

60.541

19.952

5.330

2.881

6.054

1.995

Table 2SUMMARY OF MEASURED EARTH RESISTANCE READINGS AFTER ONE YEAR

Backfill material Resistance on Day 0 () Resistance after one year ()

PKF

Kenaf fibre

Paddy dust

Bentonite

SBMC

56.00

72.60

65.40

49.20

33.70

38.10

48.50

60.00

25.40

48.20

Table 3PERCENTAGE REDUCTION OF EARTH RESISTANCE FORNEMCOMPARED TO REFERENCE INSTALLATION

Months PKF Kenaf fibre Paddy dust Bentonite SBMC

(%)

0

1

2

3

4

5

6

7

8

9

10

11

12

365 days

12.91

44.42

49.77

50.44

50.84

53.32

44.30

45.66

42.18

44.78

44.88

34.37

29.43

34.65

12.91

10.96

28.01

29.30

30.46

32.78

22.81

0.39

1.58

21.89

34.33

22.30

17.36

16.81

1.71

15.12

37.50

31.50

28.15

30.91

18.82

1.54

16.27

3.00

10.08

7.86

3.40

2.92

23.48

52.93

54.63

56.39

58.40

57.47

55.70

57.23

54.66

54.36

57.80

57.22

57.17

56.43

47.59

47.26

53.47

49.78

49.58

44.61

39.16

40.46

25.91

19.94

21.89

19.93

22.64

17.32


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REFERENCES

[1] Hinde, S., Overhead Line Guidelines. British Columbia Safety Authority

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[4] IEEE Std 142-2007 Recommended Practice for Grounding of Industrial andCommercial Power Systems.

[5] BS7430 Code of Practice for Earthing..

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[14] Gomes, C., Lalitha, C., and Priyadarshanee, C., Improvement of Earthing

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Reduction of Earth Resistance Using Agricultural Waste Materials as Back-fill.PDF