A Heuristic Approach To Effective Grounding in Africa

A HEURISTIC APPROACH TO EFFECTIVE GROUNDING IN AFRICA Frank Kulor, Elisha D. Markus, Wellington M. Apprey Abstract— Safe operation and proper functioning of any electrical appliance is determined by the effective provision of grounding or earthing. Electrical grounding systems serves two important purposes. Firstly, to disperse fault caused by excessive current developed in the system into the general mass of the earth without causing any potential hazard to people or danger to the electrical system itself. Secondly, to create reference ground potential for all electrical and electronic system operation. This paper discusses the basic principles behind the effectiveness of grounding systems and how grounding is related to safety and effective operation of circuit protective devices. The focus of the study is geared towards finding low cost but effective and efficient grounding system for use in rural areas. The developed earthing system is used for the protection of domestic electrical installation and industrial/electrical power station power plants. These principles are implemented in a typical rural area in Ghana and tested by creating an artificial ground fault. The results indicate effective protection of appliances installed and tested. Index Terms— effective systems, heuristic approach 1 grounding, grounding INTRODUCTION An effective grounding system plays an important role in the safe operation of electrical appliances at home and general well-being of power systems. Grounding is essential and mandatory as it keeps people safe and helps to prevent electric shocks. It provides reference potential for proper use of power system equipment to enhance effective utilization of electrical energy [6]. Furthermore, it ensures low resistance discharge path for any travelling waves caused by lightning strikes to protect erected structures such as telecommunication masts, power lines, buildings etc. Finally, grounding systems provide a return path for any fault current or leakage current developed within installation or equipment to the general mass of the earth and subsequently cause protective device to react [1]. F.Kulor, Central University of Technology, Private Bag X20539, Bloemfontein 9300, South Africa (e-mail: [email protected]). E.D. Markus, Central University of Technology, Private Bag X20539, Bloemfontein 9300, South Africa (e-mail: [email protected]). W.M. Apprey Electrical Department, GPHA, Tema (e-mail: [email protected]). In order to maintain reference potential for safe operation of instrument, reduce equipment ground voltage to minimum and provide protection against static electric discharge, a low grounding resistance is required and the specific value will depend on the proper design and installation of the system at hand [2]. Ideally, ground is a poor conductor and when subjected to a high magnitude current, it will exhibit high potential rise. A ground potential can be referred to as voltage between grounding system and reference ground. When ground fault occurs, the fault current could range between few kilo Amperes (kAs) to tens of several kilo Amperes. This poses high potential damage to people and equipment within the vicinity of the power system network. Lightning transients also produces several tens of kAs in its vicinity that could adversely affect people and consequently damage electronic and telecommunication equipment. These effects can be limited by providing systems that effectively arrest potential danger likely to occur. How can the effective arrest be achieved? It requires a practical approach to the understanding of effectiveness of the problem at hand and in this paper we explore various methods currently in use in Ghana to establish this fact. Knowing that the effectiveness of grounding system is influenced by several factors such as soil type, moisture level, environmental condition etc. [3]. In this paper we provide tests conducted using various current trends of grounding to investigate their effectiveness depending on soil characteristics [8] and low resistance material (LRM) used. In this way grounding engineers and technicians will adopt the best grounding approach when carrying out similar task on structures to ensure that a protective device will react in the event of ground fault and lightning transient waves. 2 METHODOLOGY The purpose of this experiment is to investigate and collect data on how soil type, depth of rod and the type of the backfilling low resistance material (LRM) contributes to the effectiveness of earthing. The efficient low resistance materials available are namely, raw soil, palm kernel oil cake (PKOC) and mixture of charcoal and sawdust as conductive backfill for the reduction of resistance across the earth electrode. An earth rod of 120mm long and 10mm diameter was used for each of the backfilling low resistance material in two different soil types, sandy – gravel and loamy soil at different sites and their resistance measurements compared [4]. An investigation hole of 2ft and 4ft deep was dug for both soil types at the various sites. The diameter of the hole for sandy – gravel soil was 0.053m and that of loamy soil was 0.083m. Earth rod was installed firstly in the raw soil with addition of water and also for each of the backfilling low resistance material, that is, mixture of sawdust and charcoal and for palm kernel oil cake for both 2ft and 4ft investigative holes. The earth resistance of each electrode was measured after a period of three days using the 2120ER digital earth resistance tester with a reference earth electrode with no backfill of LRM also installed at these sites for the purpose of comparison [5]. In principles, electrode resistance depend on the depth and moisture content of the soil geoelectric properties [7]. 𝛼𝑐 Rg2 = 2𝜋𝐿𝑔 √1 + ( 2𝐿𝑔 [ln ( 2𝐿𝑔 2 ) 𝑅 + 𝑅 2𝐿𝑔 2 ) 𝑅 ) {1 +√1 + ( 𝛼−𝛼𝑐 2𝜋𝐿𝑔 } + ( 𝑅 2𝐿𝑔 ) - 2𝐿 𝐷 𝐷 𝐷 2𝐿 2𝐿 (ln ( ) {1 +√1 + ( )2 } + ( ) 𝐷 -√1 + ( )2 (2) [2 & 8] 2𝐿 Where; αc = resistivity of low resistance material with thickness (m) D = diameter of hole (m) α = resistivity of soil (Ω/m) 2.3 Pit method In this method, the following equation is employed. Rg3 = +( {1 𝑅 2𝐿𝑔 𝛼−𝛼𝑐 2𝐿𝑔 2𝜋(𝐻𝛼+(𝐿𝑔−𝐻))𝛼𝑐 ) -√1 + ( +√1 + ( 2𝐿𝑔 2 ) ] 𝑅 𝐷 2𝐿𝑔 )2 } [ln ( + 𝑅 ) {1 +√1 + ( 𝐻𝛼(𝛼−𝛼𝑐) + ( 2𝐿𝑔 ) } 2𝐿 2𝜋(𝐻𝛼+(𝐿𝑔−𝐻))𝛼𝑐 𝐷 2𝐿𝑔 2 ) 𝑅 (ln ( ) 𝐷 -√1 + ( 𝐷 2𝐿𝑔 )2 ]) (3) [2 & 8] Fig. 1a. Loamy soil type 2.1 Ground arrangements method; This approach involves selection of various ground properties such as soil resistivity, radius of the buried earth electrode, ground resistance around the earth electrode area and the effective length of electrode in contact with general mass of the earth. Having obtained these parameters, equation (1) is applicable to the grounding arrangement. In these equations; α= resistivity of soil (Ω/m) R = radius of ground (m) Rg = grounding resistance (Ω) Lg = length of grounding rod (m) Rg1 = 𝛼 2𝜋𝐿𝑔 √1 + ( 2.2 Where; R = radius of rod (m) D = diameter of LRM (m) H = height of LRM (m) Fig. 1b. sandy-gravel soil type 2𝐿𝑔 [ln ( 𝑅 ) {1 +√1 + ( 2𝐿𝑔 2 ) ] 𝑅 2𝐿𝑔 2 ) 𝑅 } + ( 𝑅 2𝐿𝑔 ) - (1) [2 & 8] Hole method The Hole method is similar to the grounding approach except with slightly difference. It makes use of the diameter of the earth electrode instead of radius in the previous approach. The arrangement gives rise to equation (2) with modification in the area calculation which make these expression complex. In the event that the ground and hole method give rise to higher value of resistance, the pit method can be applied. The latter method come with sufficient accuracy employing the soil homogenous material of different layers. 3 EARTH RESISTANCE MEASUREMENT TEST PROCEDURE AND SETUP The test leads were connected to the instrument terminals E. P. C. The alligators of the test leads were short circuited after the connection to the terminals. An appropriate ohm (Ω) range was selected. The “0 Ω ADJ” dial was adjusted until the displays reads zero. The respective test leads were connected to the instrument terminals E, P and C with auxiliary spikes P1, C1 stuck into earth in a straight line where the green lead was clipped to the earth electrode under test and the yellow and red leads clipped to the auxiliary spikes at equal distance from the earth electrode under test. The function switch was rotated to a suitable range and the push button was pressed to test and lock the reading. The test setup is as shown below; Fig. 2. Test setup [9] Table 1 Test results EXP. No Sandy gravel – Sandy – gravel soil 2. Sandy gravel – Charcoal and sawdust RESULTS AND DISCUSSION The earth electrode resistance test readings were measured on the third day after installation. The values obtained are presented in table 1 which shows the measured values for both 2ft and 4ft depths with respect to their various LRMs. Figures 1a and 1b shows a graphical representation of the measured resistance values against the LRM at their respective depths. Earth electrode resistance is well known to be influenced by the moisture content of the soil. The palm kernel oil cake (PKOC) was observed to have provided the lowest and most stable resistance value for both 2ft and 4ft tests. Considering the fact that the data was taken during the rainy season and water was generously added to the mixture, the PKOC provides a considerable reduction in resistance value for both soils. The mixture of the charcoal and sawdust, although relatively more stable, cannot be compared with the resistance values for the PKOC but can be a replacement for the PKOC if not available other than the raw loamy soil. It was also observed that depth played an important factor, in that, the deeper the earth rod the lower the resistance reading. Previous results by [5] show that PKOC consist of relatively large conductive carbonaceous aggregate. This indicates the ability of PKOC to retain moisture contents for considerable period and absorbs moisture form the surrounding soil and this moisture content or property contributes more significantly in making the PKOC a good low resistance material and more efficient for the reduction of the earth resistance. Even though certain parameters of the backfilling agent were not investigated as done by [5], it is clearly seen that the PKOC provides a considerable reduction as seen in their investigation when compared with other LRMs. The approach used in this study where resistance values are considered is different from their approach. Constant water supply is provided for the test site for only three days before measurements were taken. This method has contributed to the low resistive values obtained from these measurements. BACKFILLING MATERIAL 1. Fig. 3. Backfilling materials 4 SOIL TYPE 3. Sandy gravel 4. loamy – Palm kernel oil cake Loamy soil 5. loamy Charcoal and sawdust 6. Loamy Palm kernel oil cake 4.1 DEPTH (FT) RESISTANCE TEST READING (Ω) 2 2.92 4 2.72 2 2.53 4 2.42 2 2.16 4 2.08 2 2.35 4 2.26 2 2.17 4 2.03 2 2.02 4 2.01 GRAPHICAL REPRESENTATIONS OF LRMs WITH DEPTH AGAINST RESISTANCE READING (Ω) Fig. 4. Sandy - gravel / backfilling materials with depth [3] Maslowski, Grzegorz, et al. "Current impulses in the lightning protection Fig. 4. Sandy - gravel / backfilling materials with depth system of a test house in Poland." IEEE Transactions on Electromagnetic Compatibility 57.3 (2015): 425-433. [4] Okyere, P. Y. Eduful, G. Frimpong, E. A. 2009: Evaluation of four local materials as backfill to enhance a low earth electrode resistance; Journal of Science and Technology, Vol. 29, No. 2, Aug., 2009 Fig. 5. Loamy/ backfilling materials with depth [5] Eduful, George, Joseph Ekow Cole, and F. M. Tetteh. "Palm kernel oil cake as an 5 CONCLUSION The efficiency of raw soil, mixture of sawdust and charcoal and palm kernel oil cake (PKOC) commonly used as backfilling agents for the purpose of the reduction of earth electrode resistance in Ghana has been investigated with the hope that installation professionals will gain an insight into the resistance dynamics of the various installation approaches. The experiments and study has proven clearly that the PKOC and the mixture of sawdust and charcoal provides better effective low earth resistance values with their respective depths. The raw sandy-gravel and loamy soil on the other hand is effective but will depend on the depth of the earth electrode not forgetting the moisture content and moisture holding capacity of the soil. The deeper the earth electrode the lower the earth resistance. Invariably biomass deterioration over the years cannot be ruled out and therefore we hope to conduct further investigations over a period of about 6 months to one year, taking into consideration the soil electrode resistance measurements and depth considerations and ways to improve them. alternative to earth resistance-reducing agent." Power Systems Conference and Exposition, 2009. PSCE'09. IEEE/PES. IEEE, 2009. [6] Pfeiffer, J. C. 2001: Principles of electrical grounding [7] Markiewicz, H. (Prof) & Wroclaw, A. K. (Dr.) 2003 university of technology Poland. Earthing systems – fundamental of calculation and design [8] Grzegorz, K. Grzegorz, M. Ziemba, R. Stanilaw, W. & Kamil, F. 2012: Analysis of simple grounding system installed in multilayer soil; [9] SEW 2120 ER Digital Earth Resistance REFERENCES [1] Singh, Tarlok. Installation, Commissioning and Maintenance of Electrical Equipments. SK Kataria & Sons, 2002. [2] Khan, Y., et al. "Efficient use of low resistivity material for grounding resistance reduction in high soil resistivity areas." TENCON 2010-2010 IEEE Region 10 Conference. IEEE, 2010. Tester Instruction Manual. AUTHORS BIOS AND PHOTOGRAPHS Frank Kulor was born in Kpando, Volta Region of GhanaWest Africa in 1976. He received the First degree in Electronics and Communication Engineering from All Nations University Collage in 2008 and MSc degree from the University Of Strathclyde Glasgow Scotland UK in 2011. He was with the faculty of Engineering, Department of Electrical and Electronic, Ho Technical University (HTU) Ghana, where he lectures in Control systems and Engineering Practices. He is the founder of Power Factor Limited an Electromechanical Engineering company in Ghana since 2006 where he has rich experience in Electrical and automation system for industry. He is currently pursuing doctoral studies at the Central university of Technology Free State E.D. Markus (Dr) is currently a senior lecturer in the Electrical, Electronic and Computer Engineering Department at the Central University of Technology, Free State South Africa. His research interests are nonlinear control, robotics, Power systems, Differential Flatness, Telecommunications and artificial intelligence. Wellington M. Apprey was born in Agona Swedru, Central Region of Ghana in 1985. He received Higher National Diploma (HND) in Electrical/Electronic Engineering from Ho Polytechnic in 2013 and currently completed his First Degree in Electrical/Electronic Engineering from Accra Institute of Technology in 2017. He is the Electrical Engineer for Power Factor Limited since 2014 and a teaching assistant at the Department of Electrical and Electronic, Ho Technical University (HTU) Ghana. View publication stats