Journal Paper Format

International Journal of Advanced Science and Technology Vol. 29, No. 4s, (2020), pp. 2782 - 2788

An Analysis of the Post-Flooding Resistance of the Ground Electrodes of the 22 kV and the 115 kV Power Distribution Systems in Pathum Thani Province

Nikorn Saengngam1*, Unchalee Tonggumnead2 and Yutthachai Sillapawicharn3 1Faculty of Technical Education, Rajamangala University of Technology Thanyaburi, Thailand 2Faculty of Science and Technology, Rajamangala University of Technology Thanyaburi, Thailand 3Faculty of Technical Education, Rajamangala University of Technology Thanyaburi, Thailand 1*[email protected], [email protected], [email protected]

Abstract Power system disruptions can stem from several types of natural disasters, including the rains, thunderstorms, and most notably flood. The objective of the present study is to examine the effects of flood on the resistance of the ground electrodes and the specific earth resistance of the 22 kV and the 115 kV power distribution systems in Pathum Thani, one of the provinces of Thailand most highly susceptible to flooding. The data were collected from five districts in Pathum Thani province, namely Bang Kradi, Khlong Luang, Rangsit, Lad Lum Kaeo, and Thanyaburi, using a systematic sampling technique. The research results are as follows. First, the post-flooding resistance of the ground electrodes of the 22kV power distribution systems was the highest in Thanyaburi district with the value exceeding the predetermined standard. Second, the post-flooding resistance of the ground electrodes of the 115 kV power distribution systems did not differ significantly from the predetermined standard. Finally, from an analysis of the specific earth resistance, the most suitable type of grounding for the 22 kV power distribution systems would be GR-1 for Bang Kradi and Khlong Luang districts and GR-2 for Rangsit, Lad Lum Kaeo, and Thanyaburi districts. In contrast, the most suitable type of grounding for the 115 kV power distribution systems would be GR-1 across all the districts. Based on the findings, it can thus be concluded that flood seems to have small effects on the resistance of the ground electrodes and the specific earth resistance of the power distribution systems in Pathum Thani province.

Keywords: flooding, resistance, specific earth resistance, ground electrode, power distribution systems.

1. Introduction The Provincial Electricity Authority (PEA) of Thailand has a 22 kV and 115 kV power distribution coverage through its transmission lines constructed across the country. Specifically, the transmission lines are universally grounded using ground rod electrodes with the dimensions of 60x60x5 mm. and the length of 2,000 mm. In addition, one transmission tower is installed with one ground electrode. Such a conventional approach to the construction of transmission lines clearly takes little account of different earth properties. This lack of careful consideration can result in high ground electrode resistance, poor power distribution reliability, and low natural disaster responsiveness. However, it is possible to mitigate the effects of natural disasters and thus minimize power system disruptions using preventive measures, such as external grounding in case of thunderstorms [1]. Thailand is at great power distribution risk from several types of natural disasters, including the rains, thunderstorms, and flood, especially during

International Journal of Advanced Science and Technology Vol. 29, No. 4s, (2020), pp. 2782 - 2788 monsoon season. A case in point is the Great Flood of 2011, in which water submerged the entire country, from Chiang Mai in Northern Thailand to Ayutthaya, Pathum Thani, Nonthaburi, and Bangkok in Central Thailand all the way down to provinces in Southern Thailand. Exacerbating the problem are the socioeconomic characteristics of the central region. Located here are not only as many as seven major industrial estates, namely Rojana Industrial Park, Factory Land, Ban Wa Industrial Estate, Bangpa-in Industrial Estate, Saha Rattana Nakorn Industrial Estate, Navanakorn Industrial Zone, and Bang Kradi Industrial Estate, but also a myriad of small- to medium-sized factories. Since many of these businesses employ chemical substances in their production lines, flood that arises may carry compounds with detrimental effects on ground electrodes, such as corrosion and changes in their chemical structures, conductivity, and resistance. Extensive research on the resistance of ground electrodes has been conducted. To illustrate, examined the effects of earth resistance and down conductor spans on the overvoltage of power distribution insulators [2]. It was found that changes in the earth resistance would greatly contribute to the overvoltage of only the insulators with down conductors hit by thunderbolts, while changes in the down conductor spans would have very minor effects on overvoltage. In addition, the down conductor spans that were equal to the transmission tower spans would bring the lowest backflash rate [3]. Designed a grounding system for 115 kV transmission lines to reduce backflash rates in locations with extremely high earth resistance. The study incorporated a Monte Carlo simulation technique in conjunction with ATP/EMTP software and took into consideration the following random variables: impulse current magnitudes, wave rise time, system voltages, and the locations of transmission towers struck by thunderbolts. The findings revealed that ground rods were suitable for transmission lines in locations whose specific earth resistance fell within a normal range, whereas locations with extremely high specific earth resistance would call for ground wires connected to transmission tower foundations not exceeding 30 m. in length. Additionally, with regards to the impedance surge of the transmission lines, the degrees to which the backflash rates could be reduced were minimal [4]. Investigated thunderbolt prevention techniques using ground electrodes wired to transmission tower foundations. An analysis of the earth resistance of the ground electrodes of buildings and constructions in Bangkok Metropolis and its vicinity indicated the earth resistance tested at the steel columns of the transmission tower foundations, at the ground beam steel reinforcements, and at concrete slab steel reinforcements ranged between 0.344Ω and 7.170 Ω, between 0.010 Ω and 0.727 Ω, and between 0.026 Ω and 0.114 Ω, respectively. Therefore, the present study aims to examine the effects of flood on the resistance of the ground electrodes and the specific earth resistance of 22 kV and 115 kV power distribution systems as well as to identify locations with low potential for thunderbolt mitigation, discharge flow, and power surge prevention. Ultimately, it is hoped that the findings will play a part in maintaining power quality, minimizing power system disruptions, and preventing losses to electrical equipment, measurement and related devices, property, and most importantly, life, particularly in areas within and around power stations.

2. Equipment and Procedures 2.1. Grounding Systems of the 115 kV Transmission Lines The grounding system design of the 115 kV transmission lines of the PEA reduces overvoltage at the column piers resulting from thunderbolt strikes on aerial cables and prevent insulator backflash. The earth resistance of the 115 kV transmission lines stipulated by the PEA is 10 Ω or under [5]-[6].

International Journal of Advanced Science and Technology Vol. 29, No. 4s, (2020), pp. 2782 - 2788

Figure 1. Illustrate the Waves move between the objects that different surge impedances

2.2. Grounding Systems of the 22 kV Transmission Lines The grounding system design of the 22 kV transmission lines of the PEA involves installing ground wires within the transmission towers leaving one end at the column piers and the other at the column bases for direct grounding. Consequently, measurement of the resistance of the ground electrodes had to be performed at the spots where the transformers were set up since those were where the ground wires were connected to the ground electrodes. The installation of the transformers in the power distribution systems must meet the following requirements. First, the ground wires used must be 50 mm2. galvanized steel wires, and the portions above the ground have to be shielded with 2.5 m. PVC pipes. Second, the earth resistance of the ground wires at each spot has to be no more than 5 Ω under normal circumstances and 25 Ω in locations where grounding is difficult. Third, the total earth resistance of the neutral conductors in the low-power distribution systems must not exceed 2 Ω, or will otherwise require the installation of more ground rods. Fourth, ring grounding is a preferred technique since it will help to lower the step voltage and the touch voltage around the column bases and thus to enhance operational safety. Finally, the ground wires have to be connected to the ground rods using a heat coupling technique only [5]-[6].

2.3. Procedures 2.3.1. The scope of the study was determined in Pathum Thani since it is one of the provinces with the highest rates of the rains and flood. Then, the data pertaining to the districts with the 115 kV and the 22 kV transmission towers were gathered.

Figure 2. Illustrate the flooded areas in Pathum Thani Province in the year 2011

Illustrate the flooded areas in Pathum Thani Province in the year 2011 [7].

International Journal of Advanced Science and Technology Vol. 29, No. 4s, (2020), pp. 2782 - 2788

2.3.2. From the districts with the 22 kV and the 115 kV transmission towers, the locations where the data were to be collected were determined using the Cochran formula:

pp(1 ) 2 n  z d 2 where p represents the estimated proportion of an attribute present in the population, which is generally 50% or 0.50 [8]. Z represents the level of significance, which is 1.96 at the significance level of 0.05 or the corresponding confidence interval of 95%. 2.3.3. The samples were selected using a systematic random sampling technique following the procedures below. n 2.3.3.1. The sampling interval was determined from k  , where N represents the N population size and n represents the sample size. 2.3.3.2. All sample units constituting the population were assigned numbers. 2.3.3.3. Random numbers (r) with a value between 1 and k, i.e. 1 < r < k, were selected. The samples assigned the numbers matching r, r+k, r+2k,… r+(n-1)k were the desired units. 2.3.4. The resistance of the ground electrodes and the specific earth resistance of the 22 kV and the 115 kV power distribution systems in Pathum Thani province was measured. 2.3.5. The values obtained were simulated using a Monte Carlo technique to identify locations likely to encounter difficulties in thunderbolt mitigation, discharge flow, and power surge prevention. 2.3.6. The values obtained were compared to the predetermined standard using the following formula [9].

X   t  0 Sn/ where t represents the test statistic. X represents the mean of the sample values.

0 represents the predetermined standard. S represents the standard deviation of the sample values. n represents the sample size.

2.3.7. From 2.3.1-2.3.6, the parameters to be examined were:  The resistance of the ground electrodes of the 115 kV power distribution systems from 21 locations in Rangsit district, 20 locations in Lad Lum Kaeo district, and 20 locations in Bang Kradi district.  The resistance of the ground electrodes of the 22 kV power distribution systems from 21 locations in Rangsit district, 20 locations in Lad Lum Kaeo district, 19 locations in Khlong Luang district, 19 locations in Thanyaburi district, and 20 locations in Bang Kradi district.  The specific earth resistance from 30 locations in Rangsit, Lad Lum Kaeo, Khlong Luang, Thanyaburi, and Bang Kradi districts.

International Journal of Advanced Science and Technology Vol. 29, No. 4s, (2020), pp. 2782 - 2788

3. Results and Analysis The findings are divided into two sections: the resistance of the ground electrodes of the 115 kV and the 22 kV power distribution systems and the specific earth resistance

3.1. Resistance of the Ground Electrodes of the 115 kV and the 22 kV Power Distribution Systems As for the resistance of the ground electrodes of the 115 kV power distribution systems, the highest mean value was found for Bang Kradi district, followed by Lad Lum Kaeo and Rangsit districts, respectively. A further analysis revealed that the resistance of the ground electrodes of the three districts did not differ from the predetermined standard of 10 Ω at the significance level of 0.05. Details are shown in Table 1-2 and Figure 3.

Table 1. The minimum, maximum, average and standard deviation of the resistance of the ground electrodes of the 115 kV in Rangsit district, Lat Lum Kaeo district, and Bang Kradi district

Electricity Areas Min Max X S Rangsit 0.34 48.40 5.24 12.14 Lad Lum Kaeo 0.34 39.30 5.67 9.96 Bang Kradi 0.66 96.57 15.23 26.72

Figure 3. Illustrate the resistance of the ground electrodes of the 115 kV comparison between Rangsit district, Lat Lum Kaeo district, and Bang Kradi district

Table 2. Compares the different between the predetermined standard (10 Ω) and the resistance of the ground electrodes of the 115 kV in Rangsit district, Lat Lum Kaeo district, and Bang Kradi district Electricity t-Value p-Value 95% Confidence Interval of the Different Areas Lower Upper Rangsit -1.97 0.09 -10.29 0.76 Lad Lum Kaeo -1.94 0.07 -8.99 0.33 Bang Kradi 0.91 0.38 -6.88 17.45 In terms of the resistance of the ground electrodes of the 22 kV power distribution systems, it was found that Thanyaburi district had the highest mean value, followed by Bang Kradi, Rangsit, Khlong Luang, and Lad Lum Kaeo districts, respectively. A further analysis indicated that among the five districts, the resistance of the ground electrodes in Rangsit and Bang Kradi districts did not deviate significantly from the predetermined

International Journal of Advanced Science and Technology Vol. 29, No. 4s, (2020), pp. 2782 - 2788 standard of 5 Ω at the significance level of 0.05. In contrast, the resistance of the ground electrodes in Lad Lum Kaeo, Khlong Luang, and Thanyaburi districts differ significantly from the predetermined standard of 5 Ω at the significance level of 0.05 with the mean value for Thanyaburi district higher than the predetermined standard of 5 Ω, while the mean value for Khlong Luang and Lad Lum Kaeo lower than the predetermined standard. Details are shown in Table 3-4 and Figure 4.

Table 3. The minimum, maximum, average and standard deviation of the resistance of the ground electrodes of the 22 kV in Rangsit district, Lat Lum Kaeo district, Khlong Luang district, Thanyaburi district and Bang Kradi District

Electricity Areas Min Max X S Rangsit 0.66 27.90 5.42 5.73 Lad Lum Kaeo 0.56 3.34 1.47 0.96 Khlong Luang 0.25 7.20 3.42 1.92 Thanyaburi 2.02 36.60 10.41 10.14 Bang Kradi 1.52 55.80 6.45 11.74

Figure 4. Illustrate the resistance of the ground electrodes of the 22 kV comparison between Rangsit district, Lat Lum Kaeo district, Khlong Luang district, Thanyaburi district and Bang Kradi district

Table 4. Compares the different between the predetermined standard (5 Ω) and the resistance of the ground electrodes of the 22 kV in Rangsit district, Lat Lum Kaeo district, Khlong Luang district, Thanyaburi district and Bang Kradi district Electricity t-Value p-Value 95% Confidence Areas Interval of the Different Lower Upper Rangsit 0.33 0.75 -2.26 3.11 Lad Lum Kaeo -16.82 0.00 -3.97 -3.09 Khlong Luang -3.58 0.002 -2.50 -0.652 Thanyaburi 2.32 0.03 0.52 10.52 Bang Kradi 0.55 0.59 -4.09 6.94

International Journal of Advanced Science and Technology Vol. 29, No. 4s, (2020), pp. 2782 - 2788

3.2. Specific Earth Resistance An analysis of the specific earth resistance measured from 30 locations in Rangsit, Lad Lum Kaeo, Khlong Luang, Thanyaburi, and Bang Kradi districts illustrated that the most suitable type of grounding would be GR-1 for the 22 kV power distribution systems in Khlong Luang and Bang Kradi districts but GR-2 for those in Rangsit, Lad Lum Kaeo, and Thanyaburi districts. In comparison, the most suitable type of grounding for the 115 kV power distribution systems would be GR-1 across all the five districts under investigation.

4. Discussion As the findings show, the resistance of the ground electrodes of the 22 kV and the 115 kV power distribution systems was over the predetermined standards in some districts, such as Thanyaburi. From visual inspections during the field surveys, this was attributable to the deterioration of the physical properties of the above-ground wires caused by the accumulation of large amounts of dirt and rust, chemical corrosion, and PVC pipe degeneration following continued exposure to excessive heat, thunderbolts, and flood.

5. Conclusion Further research along this line should take into consideration such factors as earth density since it has a significant impact on accuracy in the measurement of the resistance of ground electrodes. In addition, it should involve scrupulous examination to ensure that there is no wear and tear to ground electrodes. Finally, careful consideration should be given to the physical and chemical properties of ground electrodes in order to invent more durable material that can withstand degeneration for a longer period of time.

Acknowledgment The authors gratefully acknowledge the participating in the Faculty of Technical Education, Rajamangala University of Technology Thanyaburi and National Research council of Thailand. We are also thankful to those who could not be mentioned here for their kindness and encouragement.

References [1] Division of Standards Electrical System. Department of Standards and Safety. Provincial Electricity Authority. (2007). “PEA 115 kV transmission system construction”. [2] Rasthapoom Khumsiri. (2005). “Alternative: A Study on Effect of Ground Resistance and Span of Down Conductor on Over Voltage across Insulators for Distribution System”. Master thesis, King Mongkut University of Technology Thonburi. [3] Winai Boonrawd. (2005). “Grounding System design for Reduce Back flash Rate of 115 kV Transmission Line in High Soil Resistivity Area”. Master thesis, Kasetsart University, Thailand. [4] Anawat Wannasri. (2008). “A Study of Grounding for Lightning Protection System using Foundation Earth Electrode”. Master thesis, Kasetsart University, Thailand. [5] Grounding design calculation for 115/22 kV omnoi3 substation (PEA). [6] IEEE Std. 142-1991. (1992). IEEE Recommended Practice for Grounding of Industrial and Commercial Power Systems. United States of America: Institute of Electrical and Electronics Engineering (IEEE). [7] “Geo-Informatics center for Thailand”. http://www.gisthai.org/pics/flood55-resize3.gif . [8] Cochran, WG (1963). “Sampling Techniques”, John Wiley and Sons, New York. (1961). [9] Cressie, N. (1980). “Relaxing assumptions in the one sample t‐test”. Australian Journal of Statistics, 22(2), pp.143-153.