Vol. 39(2), pp. 227-245, Dec. 2020 Tanzania Journal of Engineering and Technology ISSN 1821-536X (print) Copyright © 2020 College of Engineering and ISSN 2619-8789 (electronic) Technology, University of Dar es Salaam

Review Paper Potential for Increased Rural Electrification Rate in Sub-Saharan Africa using SWER Power Distribution Networks

Michael E. Irechukwu and Aviti T. Mushi

Department of Electrical Engineering, University of Dar es Salaam, Tanzania. *Corresponding Author E-mail: [email protected]

ABSTRACT Rural electrification rate (RER) in Africa is still low to date. Several countries in Sub-Saharan Africa have tried to address this problem using conventional single- phase two-wire or three-phase three-wire systems, however at large costs due to the nature of dispersed rural load centres, low load demand, and low population density. Another solution of off-grid generation creates associated health problems. Therefore, this paper undertakes a review of a single wire earth return (SWER) network as a RER improvement solution. The paper undertakes intensive literature review to elucidate challenges and solutions to the implementation of SWER technology. Advantages of SWER technology discussed make it the choice for RER improvement in Sub-Saharan African countries. After that, a case study is selected in rural Tanzania, and a preliminary SWER network design is undertaken.

Keywords: Single wire earth return (SWER), power distribution networks, rural electrification rate (RER).

INTRODUCTION governments of South Africa and Zimbabwe invested huge amounts of Majority of grid-connected rural money to rural electrification projects electrification (RE) technology in Africa using these conventional technologies are the single-phase two-wire (SPTW) (Davidson and Mwakasonda, 2004). The distribution system and the three-phase second barrier is the scattered rural three wire (TPTW) distribution system, population which results in low demand called conventional technologies. per connection, thus producing low Mahanthege (2015) cited a study that benefit-cost-ratio ( ). The third barrier presented data of rural electrification rate is low population density in rural areas (RER) in Sub-Saharan Africa at about with low-income levels, thus resulting to 14.2%. This is an alarming situation that small sized electricity demand. These three suggests of existence of barriers to are thought to discourage utilities in achieving higher RER in some perspective. increasing RER in Sub-Saharan Africa The literature suggests that the first barrier (Golumbeanu and Barnes, 2013). As such to be high investment cost of installing to reverse this trend, for these poor SPTW and TPTW because of using two or countries the access to electricity must more conductors which necessitate preferably be planned as one component of erecting large number of poles to support a rural development process (Zoomers, these heavy lines. For example, the 2014). One might suggest the local

227 Tanzania Journal of Engineering and Technology (Tanz. J. Engrg. Technol.), Vol. 39 (No. 2), Dec. 2020 Michael E. Irechukwu and Aviti T. Mushi generation of electricity using available aspect of SWER technology in Africa. fossil fuels to effectuate RER This lack of literature causes lack of improvement, as a solution. However, comprehensive understanding of the local generators that produce electricity benefits and/or drawbacks of SWER thermally have been shown to cause health technology for Africa, especially the rural problems – diseases of several kinds, in Sri applications. For example, a proposed Lanka (SLEMA, 2020). This is due to the SWER design in Botswana showed drastic fumes, emissions, etc. that are produced as cost reduction of about 17.83% the cost of by-products of the 33 kV TPTW (Anderson, 2002). process. Other places of Africa have Therefore, this paper is an attempt to proposed RER improvement through solar address this literature and knowledge gap minigrids such as those found in Kenya, by providing a systemic analysis of and Uganda (Bahaj et al., 2020). This available literature and document all improved RER act as a bringer of benefits and drawbacks that have been or economic improvements to the can be accrued by the African countries by populations, since technological utilizing SWER technology. developments happen with reliable power (Ferguson et al., 2000). CHALLENGES LIMITING WORLDWIDE APPLICATIONS OF However, there is a technology that uses SWER single wire that can effectively supply scattered rural populations at a supposedly This section presents challenges that cost-effective method. This technology is plague and as a result limit pervasive called single wire earth return (SWER) applicability of SWER technologies distribution system. The technology calls globally and especially Sub-Sahara Africa. for stringent voltage and current limits These challenges include, but not limited observance so that the dangers arising to, high benefit-cost-ratio; low load from touch and step potential are capacity; high reactive losses (Momoh et alleviated. It was developed and first al., 2019); more than average energy implemented in New Zealand around 1925 losses of the conventional technologies; (Mandeno, 1947), then it spread to and voltage regulation. Australia (Nobbs, 2012). Further, it has been implemented in Sri Lanka High Benefit-Cost-Ratio (Mahanthege, 2015), Brazil (Luciano et al., 2012), Namibia (Himmel and Huysen, Rural electrification rate can be measured 2002), South Africa (Kessides et al., using a metric called benefit-cost-ratio 2007), Tunisia (Cecelski et al., 2005), ( ). The ratio should be to Ghana (Iliceto et al., 1989) and Uganda deliver net value to the utility’s project. (Bakkabulindi et al., 2012; Bakkabulindi Others denote it as BCR (Karki, 2004), et al., 2009; Da Silva et al., 2001). while others call it benefit cost analysis Realizing the potential of SWER, some factor (Parmar, 2016; Sidhu et al., 2018). researchers suggested it as a feasible The RER in Sub-Saharan Africa has electrification for a settlement in Rwanda slightly increased from 5% in 2002 (Solange, 2017); Tanzania (Irechukwu, (Davidson and Mwakasonda, 2004) to 2020; Irechukwu and Mushi, 2021; Meijer, 22% in 2017 (IEA, IRENA, UNSD, WB, 1995); a minigrid extension in Uganda WHO, 2019) due to the costly nature of (Bakkabulindi, 2012); and a future rural distribution system installation faced by electrification plan for Nigeria (FMPWH, the utilities. On utilities side, this high 2016). These are very few literatures that is undesirable. On the other hand, rich elucidate the technical and economic countries such as US has achieved wider

Tanzania Journal of Engineering and Technology (Tanz. J. Engrg. Technol.), Vol. 39 (No. 2), Dec. 2020 228 Potential for Increased Rural Electrification Rate in Sub-Saharan Africa using SWER Power Distribution Networks access to electricity in the scattered rural in rural areas because of low consumption communities by subsidizing companies or (Karki, 2004; Maunsell Limited, 2006; utilities which install electricity Rudnick et al., 2014). Despite these distribution infrastructures (Yuan, 2015), challenges, Cuba has achieved 28.8% and as such it has provided low-cost for its SWER implementation compared if technologies for rural electrification, one they used the conventional TPTW being the SWER. This has been achieved, (Monteagudo, 2014). for these projects, by realizing low defined as follows (NER, 2001). Voltage Regulation and Transmission Loss Issues ………. (1) Second challenge that faces applicability of SWER system is voltage regulation Benefit-cost-ratio in (1) incorporates the (VR) and transmission losses. This system following variables: the present value for can efficiently supply loads connected electricity sales denoted as , the within 25 km from the distribution amount of electricity in kWh sold in a year transformers (Louie et al., 2015), thus it denoted as , the value of electricity in can be modelled as a short transmission kWh denoted as , the discounted value line. Consider Figure 1 showing a model of investment stream denoted as , the of this short transmission line of length discounted value of operations and 80 km. The variables are: sending end maintenance costs each year denoted as voltage denoted by , sending end current , the present value of losses denoted denoted by , resistance and reactance as , the long range marginal cost for expressed as and both measured in distribution denoted as , the kWh /m. Therefore, for line of length forms losses in a year denoted as . However, line impedance , receiving end this is easy to plan for but harder to current and voltage denoted by and implement because other factors challenge respectively. cheap SWER technology implementation

Figure 1: Model of a short transmission line with two wires.

Therefore, using Kirchhoff’s current and voltage laws (KVL and KCL) with Equation (2) has the following parameters: parameters, equation (2) is obtained , , and S. (Grainger and Stevenson, 1994). Therefore, line regulation ( ) and line loss ( ) are defined by Equation (3) and (4), respectively. ………..………… (2)

229 Tanzania Journal of Engineering and Technology (Tanz. J. Engrg. Technol.), Vol. 39 (No. 2), Dec. 2020 Michael E. Irechukwu and Aviti T. Mushi

………..….. (3) distribution network losses from 16% in 1926 to 7%, globally (ETSAP, 2014).

Carson’s Line Model ……………….. (4) Carson (1926) pioneered the derivations These equations contain the following that computed the impedances of overhead variables: and are the conductors with earth return. Other angle of the sending end and receiving end researchers (Ciric et al., 2004; Kersting, respectively. The single line design of 2005; Kersting and Green, 2011) used the SWER in Figure 1 poses a challenge to inspiration of Carson’s work to compute maintain these (3) – (4) in acceptable the impedances using numerical methods. limits. Here, the deciding factor is the They considered the Carson’s line to be a impedance and power factor. Voltage modification of Figure 1 in the following fluctuation (or regulation) is reported to way. A single return conductor with a self- challenge the high penetration of solar geometric mean radius (GMR) of unit photovoltaic (PV) energy into the SWER length conductor running parallel to distribution system (Guinane et al., 2012). the ground (earth), carrying current , Results show voltage rises across the low with its return circuit beneath the voltage (LV) network exceeding earth (also known as the fictitious regulatory standards with the high conductor). The return conductor is located penetration of PV in SWER networks. at a distance below the overhead line, These networks could also be fed on both ends using PV and SWER, backed up by a shown in Figure 2. This depends on diesel generator in a bidirectional setup, the soil resistivity ( , thus different soils such as the one in Philippines (Sumaya et will have different characteristics shown in al., 2019). Technology advances e.g., Table 1 (Samra, 1972). The variable is efficient transformers, better cable design, the self-impedance of the line, is the etc. have enabled the reduction of ground mutual impedance, and is the ground self-impedance.

Figure 2: Model of a Carson’ line (Ciric et al., 2004)

Tanzania Journal of Engineering and Technology (Tanz. J. Engrg. Technol.), Vol. 39 (No. 2), Dec. 2020 230 Potential for Increased Rural Electrification Rate in Sub-Saharan Africa using SWER Power Distribution Networks

Table 1: Soil Resistivity (Source: Samra, 1972)

Ground type Organic wet soil Moist soil Dry soil Bedrock Unit Resistivity ( 10 100 1,000 10,000

Using the KVL, the Carson’s line medium earth resistivity ( ), because this equations are obtained as equation (5), allows cheap cost of grounding the which is a modification of equation (2) earthing electrodes and protection of because of the ground return effect. Where equipment (Iliceto et al., 1989). Therefore, the potential drops , , , and are it is of utmost importance to prevent dry all measured with respect to same out soil by fast evaporation near the reference ( ). electrodes, as this will cause an uncontrolled increase in resistance and cause thermal instability, which is checked …….. (5) by employing Ollendorff formula (Iliceto et al., 1989). Further manipulation of equation (5) yields the potential as the function of line self- ……………………. (8) impedance, ground correction factors and the line current, see equation (6). The Where is potential of electrode above ground correction factor is approximated that of earth; is heat conductivity of the by ground self and mutual impedances soil; and is the temperature rise of the as in equation (7). Further electrodes and contiguous soil above the computations pertaining to equation (7) are ambient. Soil resistivity is affected by , outlined by Ciric et al. (2004). moisture, and percentage of salts in the soil. Practically, for 50 Hz currents, the ... (6) earth path that allows the current to flow is limited by the skin depth ( ). ……………. (7) Conservatively, the current density should not exceed 200 A/m2, in the vicinity of the grounded electrode for more than one Ground Resistance second (Meijer, 1995). The efficient grounding was experimentally shown to Design challenge faced in the installation result to maximum and efficient power of SWER system is ensuring that the earth transfer (Neste et al., 2016), albeit that was resistance ( ) at the isolation and a wireless system. distribution transformer is within acceptable limits (Nebi et al., 2017; Limited Power Handling Capability Solange, 2017). The isolation transformer is very important because it is often used Power is supposed to flow with minimal to prevent the SWER ground currents from losses in a SWER network, as was causing earth current faults on the main previously shown by equation (4). Using medium voltage (MV) network. There Figure 2 and taking node to enclose point have been cases of burning of earthing and node to enclose point then the electrodes and wooden poles due to poor power flow can be computed by Equations earthing (Catriz et al., 2019; Nobbs, 2012), (9) – (11) observing the power mismatch and this is expensive as this hardware has criteria equations (12) – (13). The to be replaced after every burning. To variables are explained as following: - avoid such dangers and costs, the and are current injections at node ; installation site must possess low or

231 Tanzania Journal of Engineering and Technology (Tanz. J. Engrg. Technol.), Vol. 39 (No. 2), Dec. 2020 Michael E. Irechukwu and Aviti T. Mushi

and are the scheduled power improve voltage profile, power factor, and injection at node ; is the admittance of voltage stability of the network. all shunt elements at node ; is the admittance of all ground mutual shunt Improving Voltage Profile elements; and are phase voltage Voltage profile of a SWER line can be and ground voltage at node ; and improved using single phase voltage are current flowing on a section of the regulators. However, these may not SWER line; is the set of line function so well if a large increase on load sections connected downstream to node ; demand on SWER line happens with and and are power mismatches accompanied voltage distortions or VR at node . (Hosseinzadeh et al., 2011). In this case an upgrading of a SWER system to handle ..(9) this VR problem is proposed using either switched reactors, saturable reactors (Mayer et al., 2006) or DSTATCOMS. However, this comes at a high cost to the ………. (10) installation (Mirazimiabarghouei, 2017). The DSTATCOMS works better whenever they are installed on the customer side to …... (11) provide the needed voltage support, rather than upstream in the network. The .... (12) DSTATCOMS can cause peak value of line voltage limit at the customer terminal by injecting active ( ) and reactive ( ) .. (13) …………… …… power at constant apparent power ( ). This action ensures stable operation of the line. Single wire earth return networks can reach their power and voltage design Other studies (Kashem and Ledwich, capacity due to unprecedented electrical 2004; Kashem and Ledwich, 2002) demand brought about by proliferation of proposed installation of distributed end user loads. When this happens, generators (DG) in the SWER network to switched capacitors can be employed to aid in improving voltage profiles, reduce provide voltage support (Shammah et al., the system losses as well as costs 2013). This solution was also deployed by (Hosseinzadeh and Rattray, 2008; Vo et Ergon Energy (Lowry et al., 2012). Ergon al., 2013). These DGs control system is set implemented it in the Queensland’s 64,000 to respond very fast to system changes, km of SWER networks and its efficacy thus performs power factor correction and was verified experimentally. In addition, correct any VR while at the same time they alleviate or reduce charging helping to reduce power losses in the capacitance current associated with SWER system. System reliability is Ferranti effect on long SWER lines. improved as well. The reliability Distribution static compensators improvement is due to the SWER design (DSTATCOM) discussed by being able to carry less reactive and active Mirazimiabarghouei (2017) and losses in the system compared to the Mirazimiabarghouei et al. (2016) are conventional technologies (Bank, 2018). installed to regulate the flow of reactive power by injecting or absorbing it from the distribution networks, when the need be, to

Tanzania Journal of Engineering and Technology (Tanz. J. Engrg. Technol.), Vol. 39 (No. 2), Dec. 2020 232 Potential for Increased Rural Electrification Rate in Sub-Saharan Africa using SWER Power Distribution Networks

THE DESIGN OF SWER Duplication of the ground points assures DISTRIBUTION SYSTEM that the system is still safe if either of the grounds is damaged. In fact, the duplicated Single wire earth return (SWER) system is ground in SWER leads to zeroing (Bank, composed of the following components 2012) because the resistance on the ground (Brooking et al., 1992): (1) isolation between them is much greater than the transformer with rated voltage 11 kV/ 6.35 resistance of the wire. kV and power rating 25 – 300 kVA; (2) distribution primary 6.35 kV and two Cost Structure of SWER Network secondary low voltages of 230 V or 240 V; Comparing with Conventional (3) aluminium steel clad steel reinforced Technologies (ACSR) conductor; (4) earthing system which also is the return path; (5) support The SWER network attracts capital costs poles – either stainless steel or wooden; at around 55.5% of an equivalent SPTW and (6) the transformer secondary is network (EU Energy Initiative, 2015). In protected by a standard high-rupture addition, SWER cost is about 40% of a capacity (HRC) fuse or low voltage TPTW network costs. One might ask, how . Figure 3 shows the does the cost saving occur? The answer is complete SWER distribution system from the massive reduction in the hardware to the grid to the customer supply side. be used in SWER erection as compared to those conventional methods. Safety Feature of SWER Line Pragmatically, it can be looked at as follows: TPTW requires seven (07) poles The SWER line does not use the common per km with spans of 100 to 150 m; while electrical safety feature – since it lacks a SWER requires spans of about 400 m thus traditional metallic return to a neutral reducing the poles per km to 2.5 poles shared by the generator. Instead, the safety (The World Bank, 2006). is assured from its design of isolation transformers. These isolate the ground On its entirety, SWER distribution system from both the generator and user. is a very simple structure to construct However, still there is possibility of stray because it only requires one live wire and voltages injuring people and livestock in the earth as return conductor. However, the vicinity of the line. Therefore, this is easier said than what the actual grounding is critical to ensure that only 8 construction takes, since lack of technical A is the limit of ground current flowing know-how limits its applicability in Sub- (Grad, 2014). These earth grounds are Sahara region. duplicated to assure increased safety.

233 Tanzania Journal of Engineering and Technology (Tanz. J. Engrg. Technol.), Vol. 39 (No. 2), Dec. 2020 Michael E. Irechukwu and Aviti T. Mushi

Figure 3: Configuration of SWER distribution system –isolation transformer rated 11 kV/6.35 kV, distribution transformer rated 6.35 kV/240V, and customer side

The limited technical know-how SWER TECHNOLOGIES IN Despite the envisaged low investment AFRICAN COUNTRIES costs required for SWER implementation, the technology has not been widely Australia has always been a leader in incorporated into power distribution application of SWER technology. For planning in Sub-Saharan Africa, thereby example, by year 2012 she had installed rendering vast regions un-electrified. This total of 64,000 km of SWER lines (Lowry is thought to be brought about by limited et al., 2012). This is a big contrast to the or lack of sufficient technical know-how few African countries that have installed that is prevalent in many utilities in the few km of SWER technology to increase region. In 2010, it was estimated that some RER so that they may improve quality of 2.5 million new engineers and technicians life (Karki, 2004). African countries that would be needed in sub-Saharan Africa have successfully installed SWER are alone if that region is to achieve some of Namibia (Momoh et al., 2019), Tunisia, the Millennium Development Goals and South Africa. In this section, the paper (UNESCO, 2010). For example, in will present the implications of the SWER Tanzania, the University of Dar es Salaam on RER of these mentioned countries. currently graduates about 60 electrical engineering students per year. The Namibia situation in other regions of sub-Saharan Africa is not very much different. That Prior to 1998, Namibia power utility, number of skilled engineering graduates is namely NamPower used to connect to the not enough to allow fully devotion to work grid about 5,700 rural households annually on SWER technology, to reap its benefits. at a cost of US$ 923 per connection However, with time and proper investment (Himmel and Huysen, 2002; AEI, 2012). in engineering education, this trend might This trend changed when the utility change for the better (The World Bank, adopted SWER technology, for whence the 2014). connections rose to 14,800 rural

Tanzania Journal of Engineering and Technology (Tanz. J. Engrg. Technol.), Vol. 39 (No. 2), Dec. 2020 234 Potential for Increased Rural Electrification Rate in Sub-Saharan Africa using SWER Power Distribution Networks households connected annually at a cost of reduction of 40% of the cost per US$ 384.6 per connection. Table 1 shows connection scenario comparing to before this 260% connection increment at a SWER, which is thus an improved RER.

Table 1: Costs and connections before and after SWER adoption in Namibia (AEI, 2012; Himmel and Huysen, 2002)

Period Cost (US$/Connection) Connections/Year Before 1998– conventional 923 5,700 After 1998 – adoption of SWER 384.6 14,800

South Africa connections per year (NER, 2001). This was possible because the connection costs Eskom, the power utility of South Africa dropped from US$ 1,000 per connection to adopted SWER applications in the year US$ 445, and as a result the SWER’s cost 1992 (Eskom, 1996). This move boosted per km became US$ 3,650 a very low , the RER from 28% to 42% by 2001 (AEI, therefore, profitable to the utility and thus 2012). Consider this, before the year 1992, Table 2 displays this improvement about 80,000 rural connections were made scenario. per year. With SWER adoption, this number changed to 390,000 rural

Table 2: Costs and connections before and after SWER adoption in South Africa (AEI, 2012; Eskom, 1996; NER, 2001)

Period Cost (US$/Connection) Connections/Year Before 1992 – conventional 1,000 80,000 After 1992 – adoption of SWER 445 390,000

Tunisia installation, STEG gave it a shot in the 1990s so that they could increase the RER. The progressive Tunisian government had During the SWER implementation, a cost made increased RER one of its reduction of 26–30% as compared to development goal in the mid-1970s, MALT was realized (Cecelski et al., reaching a 6% RER. Through her utility 2005). STEG electrified about 425 villages company, Tunisian Electricity and Gas in a span of six years. Further Company (Société de l’Electricité et du implementation of SWER up to year Gaz – STEG) the country invested 2000s, achieved an 88% RER – about massively in rural electrification (Cecelski 600,000 rural connections per year. Then et al., 2005). The company decided to use consistent efforts realized 97% RER by a different technology from the year 2012 (AEI, 2012). The World Bank conventional – SPTW and TPTW, called reported a 37% cost reduction when using Mise A La Terre (MALT) which is a three SWER as opposed to conventional phase-phase/single-phase technology technologies (World Bank, 2006). The (Karhammar et al., 2006). Between 1977 information discussed in this section is to 1986, MALT enabled to raise the RER encapsulated by Table 3, showing the RER to 28% because of dramatic costs increment and massive cost reduction by reduction, thus exceeding targets implementing SWER. repeatedly. After learning about advantages realized with SWER

235 Tanzania Journal of Engineering and Technology (Tanz. J. Engrg. Technol.), Vol. 39 (No. 2), Dec. 2020 Michael E. Irechukwu and Aviti T. Mushi

Table 3: Costs and connections before and after SWER adoption in Tunisia (Cecelski et al., 2005; World Bank, 2006)

Period Cost (US$/Connection) Connections/Year Before 1990s – conventional and MALT 1,350 28,500 After 1990s – adoption of SWER 670 135,000

RURAL ELECTRIFICATION IN improvement issues on Member States SOUTHERN AFRICAN COUNTRIES level (SADC, 2010). One proposed strategy put forth by SADC is the use of In Southern African Development SWER. Table 4 shows the RER Community (SADC), cost of rural discrepancy between Southern Africa electrification by grid extension to small, Development Community (SADC) remote and dispersed loads is expensive, countries that had adopted SWER and featuring high thus leading to energy those who didn’t by the year 2006. Those poverty (Gonzalez-Eguino, 2015). This has few who had not adopted SWER exhibited acted as the main barrier for financing less than 10% RER. This shows the projects that will increase RER, thereby, promise held by application of SWER forcing these countries governments to technology to the overall rural rely heavily on foreign aid (Kimambo and electrification of SADC countries. Nielsen, 2012). However, in 2009, these countries resolved to tackle the RER

Table 4: Rural electrification levels in SADC Countries in year 2006 (Kapika and Oguah, 2018; Kimambo and Nielsen, 2012; SADC Statistical Yearbook, 2015)

Country Population (millions) Rural population (millions) RER (%) Tanzania1 40.63 30.28 49.32 Angola 20.2 9.1 4 Botswana 1.8 0.8 9 DRC 55.6 37.4 2 Lesotho 1.9 1.5 1 Malawi 12.8 10.5 1 Mozambique 20.1 13.8 2 Namibia 2 1.3 12 South Africa 48.2 19.4 50 Zambia 11.6 7.5 3 Zimbabwe 12 7.6 8 Eswatini 1.2 0.8 5 1 Tanzania was not a SADC member in year 2006 2 Tanzania RER for 2006 was not obtained, therefore authors used the data of 2013

CASE STUDY IN TANZANIA generators (Eberhard et al., 2016). To avoid planning RE as an emergency, it is Up to this point, the authors have reviewed better to partake normal conditions the applications of SWER, its challenges, planning as suggested by Khator and and its advantages in the SADC countries. Leung (1997) because of its advantages. It was shown that it is possible to assist This is suggested because of the activities other development efforts to improve RER involved – planning for the power flow, through the technology. In the outset, up to feeder and substation installation, and 2016, Tanzania’s 46% power consumption others. Therefore, this section selects a of rural areas comes from off-grid

Tanzania Journal of Engineering and Technology (Tanz. J. Engrg. Technol.), Vol. 39 (No. 2), Dec. 2020 236 Potential for Increased Rural Electrification Rate in Sub-Saharan Africa using SWER Power Distribution Networks model rural location in Tanzania and This data was used to design and size the design the electrification scheme from the transformer shown by Table 5 followed by grid, using SWER (Irechukwu, 2020; a SWER line design shown in Table 6 for Irechukwu and Mushi, 2020; Irechukwu the 20 km length. This design is based on and Mushi, 2021). This village is called consultations with Rural Energy Authority Homboza, located in Pwani (Coast) (REA) engineers and the data they Region of Tanzania at coordinates: - provided. Further, note that instead of 7.32380S and 38.82050E. It has a using single 200 kVA transformer, the population of about 1,565 people, where design has chosen two transformers rated the economic activities are small scale 100 kVA each (Table 6). Bakkabulindi et agriculture. The reason to select this al. (2013) specified ACSR for Uganda location is to impart benefits of SWER network, similarly this paper electrification to the community, which chooses the same for Homboza. All these were shown in another similar location in specifications and other materials are Tanzania (Ngowi et al., 2019), India displayed in Table 6. The grounding is (Jamasb et al., 2015), and Zimbabwe proposed using readily available materials (Davidson and Mwakasonda, 2004). such as animal dung and wood coal to Further, grid connection feasibility fasten the attainment of results and depends on community size and the minimizing cost, similar to what Adesina distance from the closest grid point and Akinbulire (2020) proposed in (Juanpera et al., 2020; Karhammar, 2006), Nigeria. Earth resistance tests are planned and for the case study of this paper, the to be carried out annually on all the community size is sparse populated, about transformers using earth resistance tester 20 km from the grid, and rural location. Da (Agugharam et al., 2020), so that if any Silva et al. (2001) showed a cost saving of problems are present, they can be arrested 29% for a RE in Uganda, if SWER is used before they can cause damage. to connect about 200,000 inhabitants of rural remote areas. It should be noted that Possible Future Expansion due to Uganda and Tanzania are geographical Increased Demand neighbours, so a solution working in one can be applied with little adaptation to The 20 km long SWER line designed for another, case in point the Ntenjeru village the Homboza village can be expanded to (Bakkabulindi et al., 2009). This is increase its capacity (Wolfs, 2005) or interesting, because few years back in the convert to TPTW system, if and when the 1990s, Meijer (1995) had already proposed load demand warrants it. These loads can electrifying Tanzania rural areas using be pump applications which work SWER technology. Current task here is efficiently on three-phase power. The cementing that work started those times conversion can be achieved by a converter back and working out a possible technology developed by an engineer implementation, starting with load demand named Charles F. Scot in the late 1890s. estimation. The technology bears his name – Scot Transformer (Wolfs, 2013). Technical Load Demand of Homboza details about how to design the Scot Transformer are covered in detail by Wolfs Field data were collected for 24-hour (2013). The second option to choose from electrical power usage by fittings and for the case of increased load growth is to appliances used in typical houses, and upgrade the network to medium voltage those that the villagers wanted to use, but SWER network using the customer data did not have at the moment (Figure 4). The (Hosseinzadeh and Mastakov, 2008). This estimated peak load was about 139.7 kW. method will provide real time solution to

237 Tanzania Journal of Engineering and Technology (Tanz. J. Engrg. Technol.), Vol. 39 (No. 2), Dec. 2020 Michael E. Irechukwu and Aviti T. Mushi the actual load growth observed giving harmonics and eliminate (or compensate) accurate required capacity upgrades. The for other disturbances such as voltage sags. third capacity enhancement technique is to employ controllable reactors which can To make the SWER network robust, increase the capacity to about 85% as was reliable, and make it long living it is the case for the North Jericho SWER line possible to monitor it using power line (Wolfs, 2005; Wolfs et al., 2007) and communications (PLC). One technology – Central Queensland line (Hesamzadeh et narrow band communication channels was al., 2008). suggested and tested by several researchers (Nkom, 2017; Nkom et al., 2018). Another The 240–0– 240 V distribution transformer is pole mounted monitoring units installed may enable the connection of motors rated on the SWER feeder (Song et al., 2017). 480 V at less than 12 kW power demand This monitoring will enable regulation and (Bakkabulindi, 2012; Monteagudo, 2014). maintenance of this network using These motors would still require the power dynamic devices (Gay et al., 2009). electronic starters to alleviate the big Further, some algorithms can be used to voltage dip during the starting. In detect and protect SWER network against addition,there is a demonstrated faults, such as high impedance faults (Kavi technology that uses three-phase-to-single- et al., 2016) so that the reliability is phase power quality conditioner, that can preserved. These must go hand in hand by be used to supply nonlinear loads, and proper estimation of the costs of three-phase inductive or capacity loads distribution systems installation, as (Da Silva and Negrao, 2018). This historically 60% of total power costs is technology adopts a dual compensation used up in the installation works strategy, which works by drawing (Baughman and Bottaro, 1975). The cost sinusoidal current that is in phase with the allocation must be properly handled so that voltage thus producing high power factor. the SWER connected customers are not It further suppresses grid voltage heavily charged; rather their life must be improved by low-cost technology.

160 140 120 100 80 60 40 Power in kWin Power 20 0

Time of the day

Figure 4: Current load demand projected for Homboza Village in 24 hours

Tanzania Journal of Engineering and Technology (Tanz. J. Engrg. Technol.), Vol. 39 (No. 2), Dec. 2020 238 Potential for Increased Rural Electrification Rate in Sub-Saharan Africa using SWER Power Distribution Networks

Table 5: Distribution transformer size for electrifying Homboza village

Parameter Value Peak total load for 171 households 139.707 kW Power factor 0.91 Peak apparent power 153.524 kVA Multiplying factor 1.3 Transformer rating 200 kVA

Table 6: Material and equipment to connect SWER from grid to Homboza village

Material Quantity Unit Wooden pole (9 m long) 250 Pieces Distribution transformer (100kVA, 11 kV/0.23 kV) 2 Pieces ACSR (50/25 mm2) 20 km Pole-top assembly (pin insulator, bolts, nuts) 250 Pieces Copper earth rod (4 ft = 1.22 m) 4 Pieces Copper earth rod connector 4 Pieces

CONCLUSIONS Agugharam T.O., Idoniboyeobu D.C. and Braide S.L. (2020). Improvement of This paper has reviewed the SWER Earthing System for Sub Transmission technology from its inception to its Station. IRE Journals, 4(4): 62–70. applicability to increase RER in Sub- Anderson G.O. (2002). Rural Saharan Africa countries. Challenges that Electrification in Botswana–A Single must be solved by utilities to adopt the Wire Earth Return Approach. Pakistan SWER technology have been outlined and Journal of Information and Technology, some solutions discussed. It was shown 1(2): 202–207. DOI: how few Sub-Saharan Africa countries 10.3923/itj.2002.202.207 benefitted from SWER technology. Then Bahaj A.S., Alam M., Blunden L.S., James this technology was suggested for P.A.B. and Kiva I. (2020). Pathways to Homboza village found in Tanzania. A Universal Electricity Access for Rural preliminary design was presented. Communities in Africa. IOP Conf. Measures to upgrade and protect this Series: Earth and Environmental designed SWER network were laid out. Science 588, 022047, 1–8. Future work might focus to perform doi:10.1088/1755-1315/588/2/022047. detailed design and cost analysis of the Bakkabulindi G. (2012). Planning Models Homboza SWER network, and use the for Single Wire Earth Return Power result for projections to other rural areas to Distribution Networks. Licentiate raise the RER within Tanzania. Thesis. Royal Institute of Technology, Stockholm, Sweden REFERENCES Bakkabulindi G., Da Silva I.P., Lugujjo E. et al., (2009). Rural Electrification Adesina L.M. and Akinbulire, T.O. (2020). Practicalities of Using Single Wire Grounding Method for Reliable Earth Return as a Low-Cost Method for Operation of Power and Distribution Grid Extension: The Case of Ntenjeru, Transformers Susbtations.” Chapter 10 in Emerging Issues in Science and Technology, 4: 105–117. DOI: 10.9734/bpi/eist/v4.

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