2017/79 Supported by k nKonw A A weldegdeg e ol n oNtoet e s eSrei r e ise s f ofro r p r&a c t hteh e nEenregryg y Etx itcrea c t i v e s G l o b a l P r a c t i c e The bottom line Rural Electrification Using Shield Wire Schemes Shield wire systems running along existing high-voltage transmission Why is this issue important? SWS technology has been deployed in several countries in lines can supply household Sub-Saharan Africa (Burkina Faso, Ethiopia, Ghana, Sierra Leone, Shield wire schemes provide a cost-effective way Togo), as well as Brazil and the Lao People’s Democratic Republic. electricity to communities located within 20 km of the to electrify villages located along high-voltage Over a period of more than 25 years, it has been used to electrify high-voltage corridor. At a fraction transmission lines 200 communities and 350,000 customers living along 2,600 km of of the cost of new substations high-voltage transmission corridors. An improved version is being In Sub-Saharan Africa, high-voltage transmission lines cross remote or independent medium-voltage readied for service in West Africa. rural communities that, despite their proximity to transmission lines, shield wire systems are lines, may be costly to connect if they are located far from existing an attractive option for rural high- and medium-voltage (HV/MV) substations. The high costs of How do shield wire schemes work? electrification, particularly in connection, combined with the low levels of electricity consumed, Three types of schemes leverage existing remote and sparsely populated often make such communities uneconomical to electrify using equipment to provide electricity to households areas that are costly to connect conventional technology. Even when financial resources are available to the grid. Systems have to wire them, it can be hard to justify spending in such cases, with and other retail customers operated successfully in Sub- the result that many potentially reachable communities go unserved. In the mid-1700s, Benjamin Franklin suggested placing iron rods atop Saharan Africa and elsewhere for At the same time, people living along the transmission corridor buildings to protect them from lightning strikes. The principle behind more than a quarter-century. A have made land available for the towers that carry the lines, gener- this practice is still applied to high-voltage lines through the use of new manual assists engineers in ally expecting to benefit through electrification of their communities. shield wires to protect the lines. The shield wires are usually connected designing and building shield wire This reasonable expectation, combined with widespread vandalism to the steel transmission towers to ground them. systems. of the towers and other equipment, makes it imperative that the To electrify communities located along a high-voltage transmis- people living along the corridor have an interest in helping the utility sion line, the shield wires are insulated from the towers and supplied Franklin K. Gbedey is a monitor the line. with medium-voltage power (usually at 34.5 kV) from the nearest HV/ senior energy specialist in Shield wire schemes (SWSs), invented in the 1980s by the late MV substation. Insulation reduces losses from capacitive coupling the World Bank’s Energy Francesco Iliceto of the University of Rome La Sapienza, provide a and prevents electromagnetic induction of current from HV lines into and Extractives Global Practice. cost-effective way to do just that. SWS technology makes it possible the shield wires. Even when insulated, the shield wires continue to to electrify communities located within 20 km of the transmission protect the high-voltage transmission line. David Vilar Ferrenbach is an energy specialist in corridor. From the HV/MV substation, the SWS can be powered along Each community is electrified through a lateral medium-voltage the same practice. a distance of 100 km with a load capacity of 3 to 5 MW. connection. The lateral connection from the shield wire may be aerial or underground, but where budgets are tight the aerial solution is Tatia Lemondzhava is an energy consultant in the same practice. Electrification with the Shield Wire Scheme in Low-Income Countries 2 R u ra l E l e c t r i f i c a t i o n Us i n g S h i e l d W i re S c h e m es FIGURE 3.2 Circuit Schematic of Three-Phase Iliceto Shield Wire Scheme Distribution for Villages, Showing Independent Figure 1. SWS with two shield wires with ground as the third phase conductor Earthing of Medium- and Low-Voltage Networks Over more than 25 years, shield wire schemes have been used to electrify 200 communities and 350,000 customers living along high-voltage transmission corridors. An improved version is being readied for service in West Africa. Note: HV = high voltage; LV = low voltage; MV = medium voltage; SWL = shield wire line; SWS = shield wire scheme. recommended. The lateral connection leads to one or more medium- Of these, the third is the most-used option, as it allows for the and low-voltage transformers that provide low-voltage supply to easy use of three-phase equipment at the customer level. Figure 1 consumers. shows a medium-voltage bypass, as well as the low-voltage power Three types of SWS are presently in operation: supply from an MV/LV transformer connected to the bypass. • A single-phase scheme with one shield wire and earth-return of A new three-phase version with two shield wires and a third current phase conductor has also recently been designed and is currently • A two-phase scheme with two shield wires being deployed in West Africa (figure 2). With the three-phase ver- • A three-phase scheme with two shield wires and the ground as sion, conventional equipment can be used to increase the reliability the third phase conductor. of the line and facilitate its operation. 3 R u ra l E l e c t r i f i c a t i o n Us i n g S h i e l d W i re S c h e m es Figure 2. New three-phase SWS with two shield wires and a third phase conductor 4.5 kV ire 3 und w ptical gro OPG W– o The cost of making medium-voltage electricity available over a shield wire line along the route of a high-voltage transmission line is between 13 and 30 percent of the cost of an equivalent conventional medium-voltage line. Underground Connection tower bare conductor Multiple grounding rods of LV network Note: HV = high voltage; LV = low voltage; MV = medium voltage. Some shield wires are equipped with optical fiber for commu- How much do shield wire schemes cost, nication purposes. Two such SWSs have been carrying communi- and what is their environmental impact? cations signals for more than a decade in Burkina Faso and Togo. In some countries, such as Ghana, the SWS has been used to power a Shield wire schemes provide medium-voltage small water treatment station and a radio-television antenna. electricity at a fraction of the cost of Equipment failures have not been observed in SWSs that were conventional medium-voltage lines, properly designed and built, with good calibration of protective while minimizing environmental intrusion relays. This is the case in Ghana, where the technology has been in successful operation for more than 25 years; Brazil, where it has The cost of insulating one or two shield wires for application of an been operational since 1995; Lao PDR, where schemes were put into SWS with earth-return of current involves only the procurement operation in 1996 and 2002; and Sierra Leone, where a scheme has and transportation of insulators and fittings and their installation on been in operation since 2010. In Burkina Faso, Ethiopia, and Togo existing shield wires. To estimate the additional costs of the three some equipment failures were caused by irregularities in acquisition phase SWS (with the earth as a conductor), the following types of or construction, primarily related to noncompliance with technical items should be taken into account: specifications. 4 R u ra l E l e c t r i f i c a t i o n Us i n g S h i e l d W i re S c h e m es • On the transmission line: Insulators, fittings, the cost of additional Summing up … Make further shield wire and structural members, and the impact of these on Shield wire schemes are an attractive option connections the bearing capacity of towers • At the supply bay for the shield wire line in the HV/MV station: for rural electrification Live Wire 2014/20. “Scaling Up Interposing transformer when needed, as an alternative to the Shield wire schemes are based on a simple technology. They use Access to Electricity: The Case tertiary winding of the HV/MV main transformer conventional equipment to supply electricity with a load capacity of of Lighting Africa,” by Daniel • The cost of the resistance-inductance grounding circuit, the cost 3–5 MW to communities located within 20 km of a high-voltage trans- Murphy and Arsh Sharma. of the capacitor bank, and the supply bay of the SWS. mission line, thus eliminating the need for additional substations. Depending on the desired specifications, schemes cost between 13 Live Wire 2014/22. “Scaling The total additional cost of a three-phase SWS with two alu- and 30 percent of an equivalent independent medium-voltage line, Up Access to Electricity: The minum-conductor, steel-reinforced (ACSR) shield wires having a making them a very attractive option for rural electrification, partic- Case of Rwanda,” by Paul cross-sectional area of 1 cm2 and a length of 100 km is estimated ularly for remote and sparsely populated communities that might Baringanire, Kabir Malik, and at $3,390/km. For the new three-phase SWS with a third conductor, otherwise be too expensive to connect. SWSs have been operating Sudeshna Ghosh Banerjee. the estimated investment cost rises to $7,590/km. Both are far less successfully in and beyond Sub-Saharan Africa for more than a Live Wire 2014/33. “Tracking than the estimate of $26,100/km for a 30 to 34.5 kV three-phase quarter-century, providing access to electricity to 135,000 previously Progress Toward Sustainable independent line with ACSR or all-aluminum-alloy conductors of the unserved customers. Energy for All in Sub-Saharan same area and an average span of about 230 meters. When designed and installed to appropriate specifications, Africa,” by Elisa Portale and In other words, the cost of making medium-voltage electricity the technology has proven very safe in operation, with a nearly Joeri de Wit. available over a shield wire line of 100 km along the route of a nonexistent environmental and social footprint. All of these factors, high-voltage transmission line is between 13 and 30 percent of the combined with the ongoing development of refinements, mean that Live Wire 2015/48. cost of an equivalent conventional medium-voltage line. SWS technology is becoming increasingly popular with energy actors “Supporting Transmission Moreover, the installation of shield wire lines avoids the need to around the world, and particularly in Sub-Saharan Africa. and Distribution Projects: acquire an independent right-of-way, which would be necessary for World Bank Investments since an independent medium-voltage line. (Even if the new medium-volt- 2010,” by Samuel Oguah, age line were routed along the high-voltage line, the right-of-way Reference Debabrata Chattopadhyay, would have to be widened.) Creating a new right-of-way or widening Iliceto, Francesco. 2016. Rural Electrification with the Shield Wire and Morgan Bazilian. an existing one for an independent medium-voltage line could affect Scheme in Low-Income Countries: Design, Construction, and local agriculture and forestry and mar the landscape. In operation, Live Wire 2017/76. Operation. ESMAP Technical Report 010/16. Washington, DC: the shield wire line does not require dedicated periodic bush clearing “Increasing the Potential of World Bank Group. http://documents.worldbank.org/curated/ and patrolling, as these activities are already performed for the Concessions to Expand Rural en/500631493652099113/pdf/114697-REVISED-JUNE12-FINAL- high-voltage line. Electrification in Sub-Saharan ESMAP-SWS-Manual-TR010-16-web-opt-REV2.pdf. Africa,” by Richard Hosier, This note is based on Rural Electrification with the Shield Wire Scheme in Morgan Bazilian, and Tatia Low-Income Countries: Design, Construction, and Operation by Francesco Lemondzhava. Iliceto, published in 2016 by the World Bank’s Energy and Extractives Global Practice (GEEDR) with support from the Energy Sector Management Assistance Program.