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Today many million people all over the world rely on electric power which has been distributed over long rural areas taking use of single-phase only. Over 20 years of experience from developing countries also shows that transmission tower shield wires can distribute significantly amount of power at very low cost to rural and remote settings. These facts, however, are still not very well communicated to national utilities, project developers and donors, engaged in rural electrification programs in poor countries. There are many reasons behind this and some are explained in this paper.

Given the fact that by simple adjustments, the cost for rural electrification can be lowered as much as 90% there is a tremendous opportunity to accelerate electrification of rural and remote areas in developing countries. However, what is needed to adopt a least-cost strategy is a systematic approach to achieve a sustainable solution, where not least-cost electrification results in downgraded performances, additional maintenance burdens, severe power limitations hampering real economic development and violation of electrical safety.

Electrification is one of the most important steps to enhance the standard of living in developing countries. It is estimated that around 2 billion people lives in areas without any electric power supply- most of then in remote and rural areas. Electrification programs in many developing countries have been undertaken during the last decades but obvious the number of people in these countries grows faster than present connection rates.

One reason for this widening “energy divide” is the high cost to reach underserved areas with electricity from existing national grids (transmission and distribution) and the high cost for small-scale local electricity generation by traditional models, typically diesel gensets. It has been observed in many developing countries that rural electrification is done using the European (3-wire) or North American (4-wire) urban standard design methods. Typically those consists of three-phase systems with relatively high power transfer capability. It is not uncommon that national utilities in these countries claim that the cost per km grid extension often to exceed USD 20,000-40,000 per km, with yearly operation and maintenance costs as high as 5% of the investment.

However, rural electrification programs have been implemented worldwide with different results and with costs per km ranging from as low as USD 3,000 per km. (See a review of standard and low-cost options)The question is why not the least costs solution are applied as they could bring forth an accelerated electrification. Many reasons have been explained to this. For example, there is a limited knowledge of the least cost solutions as three-phase electricity is “supposed to be the only alternative” for motors and other productive energy use. Further appropriate energy planning methods don’t exists for low consumption rural settings. The financing of electrification programs have been made trough bilateral donor programs and costs really not considered as the limiting factor. Early tests with e.g. single phase systems failed, due to theft of earth conductors etc.

The straight forward approach of lowering cost of rural electrification is generally very simple in its structure. I principle low-cost systems don’t differ significantly from today’s three-phase-systems. One could simply extend a system with one or two conductors instead of three. Further, reducing the conductor area gives the opportunity to increase the pole span, thereby reducing the number of poles, insulators, stay wires, etc. with significant cost reductions on both material, construction and maintenance as a result. In case of using the earth as a return conductor (SWER) very simple and cost-effective systems could be developed.

Today many countries world-wide have adopted single-phase distribution systems especially for connecting rural and remote areas. In the US, which started already in the 20-ies there are now at least 100,000 customer relying on single-phase distribution only. Most rural farms in the mid-west are still relying on single-phase distribution.

In rural Australia, New Zealand, Canada, Ireland and UK about 100,000 customer have been smoothly supplied since the 50-ies. Recent electrification in Cameroon, Cambodia, Tunisia, Morocco, Philippines, Benin, Bangladesh, Bolivia, El Salvador and Brazil have connected another 100,000 customers.

I South Africa ESKOM adopted a single-phase strategy a few years ago for electrifying rural areas like the Northern Province, Eastern Cape and KwaZulu Natal. At present at least 100,000 customers have that service.In both Ghana, Togo, Benin, Sierra Leone, Ethiopia, Laos etc. single phase distribution has been applied using the shield wires of existing transmission lines, thereby extending medium voltage supply over distances around 100 km at extremely low cost in existing transmission corridors. In total over 2200 km of shield wires are in current use in these countries.

Experiences from single-phase distribution are generally reported many times to be superior of the three-phase systems. This is mostly due to lower failure rates because of significantly lower number of critical components and reduced mechanical stress.

Economics of low-cost and single phase distribution

Single phase distribution can be implemented in at least two different ways. One is to bring out two conductors, instead of three. The other is to use only one metallic conductor and use the earth as a return conductor. The latter known as Single Phase Earth Return System (SWER)

With good conductivity of the soil the latter could typically transfer about 500 kW at distances up to 25 km at voltages of 19.1 kV and an aluminum conductor size of 75 mm². Similarly a cheaper 22 mm² steel conductor could transfer a maximum of 200 kW about 25 km at 19.1 kV and a maximum voltage drop of 5%. Introducing modern power electronic controllers (micro-FACTS) the extension could be even longer as the voltage could be restored not to exceed the 5-10 % tolerance limits.

Comparing cost for implementing the single-phase systems rather than the “standard” three-phase designs yields cost reductions down to about 40% of the traditional cost.

In Table 1 a comparison is given for three-phase designs at 33 kV and Single phase designs using different conductor sizes and pole spans.

Table 1. Cost comparison of three-phase and single-phase designs

Distribution System	Cost USD/km	Capacity kVA	Pole span	Relative cost (%)
MV System		25 km	m	%
Three phase, 3 wire, 33 kV
Aluminum 148 mm²	20,000	8,000	120	100
Aluminum 100 mm²	13,950	5,000	150	75
Aluminum 77 mm²	11,000	4,000	225	59
Aluminum 34 mm²	9,000	1,500	225	48
Steel 25 mm²	5,800	600	300	29
Single Phase, 2 wire, 33 kV
Aluminum 77 mm²	8,000	3,000	300	40
Aluminum 34 mm²	6,700	1,200	300	34
SWER, 1 wire, 19.1 kV
Aluminum 77 mm²	4,500	500	300	23
Aluminum 34 mm²	3,850	400	300	19
Steel 25 mm²	2,300	200	300	12

Least cost options can thus be found both among three phase system designs and by using different single phase configurations and essentially by changing conductor area and pole span with. For both three phase systems with 25 mm²conductors as well as single phase designs, the pole span could be extend up to as much as 600 m, depending on the actual situation, thereby reducing costs even further.

International Benchmark studies

A few years ago a study was performed to compare costs for rural electrification in a number of countries. The study showed a great variation of costs between the selected countries. In Bangladesh e.g. costs could be as low as $ 2,500 per km while in the US the cost could be as high $ 25,000 per km. In figure 1 some comparative data can be seen for both three-phase and single-phase systems. As import duties, labor cost etc. varies between the countries it could be hard to establish a world-wide cost standard. In Table 2 an attempt is made to establish a average-low benchmark, based on costs from Bangladesh.

Table 2. Cost structure of a low-cost benchmark

Technology and market barriers much related to perceptions

Despite the fact that single-phase distribution have been applied on many continents over the last decades there are little knowledge and experiences of system behavior well communicated. Many sub-Sahara utilities claim they tested e.g. SWER systems already 10-20 years ago but with bad results. Some claim that earth conductors were stolen or vandalized, resulting in power outage and safety concern. Some claim that the soil conditions were not good enough for SWER to operate.

It is also a very common perception that three phase systems are needed for the productive uses like larger motors. The availability of larger single-phase motors, up to 60-75 kW is typically not known. The conceptual idea of mixing system designs between, urban , peri-urban and rural settings is not applied and most countries apply a common urban standard, capable of transmitting many MW of power, despite the extremely low loads. Very little effort has been done trough donor and bank lending programs to adopt new least cost designs, based on actual demands and more conservative load prediction methods.

Reducing costs of electric distribution systems

There are a variety of approaches to reducing the cost of distribution lines, like e.g.;

More appropriate design specification needed

One reason why rural electrification in many developing countries exclude single-phase system options is that planning criteria are inappropriate. For example time horizons for load growth are set to 25 years. Adding to this are also conservative design factors for excess loads of wind, temperature and other mechanical loads. In Burkina Faso it was found that transmission line design was done according to European norms, thus allowing for ice-loads. Obviously there is a need for revising the design specifications to better comply with local climatic and environmental conditions.

When aggregating rural and remote loads it is further common to linearly add individual loads without any statistical modification. Typically household loads are oversized and combinatory effects from e.g. load management are typically neglected. These factors all add to heavily overestimate load and load growth.

Standardized pre-calculated designs and simpler construction methods including pre-qualified equipment and material kits

A method commonly used to lower cost of electric distribution is to standardize designs and only use these. The Swedish EBR system was e.g. adopted some 30 years ago and now all electric utilities refer to these designs. However, the designs are not only pre-calculated mechanically and electrically, but also specified when it comes to physical design and material choices. The EBR design guidelines consists therefore of a methodology in selection of appropriate components, economic calculation models, construction and installation guides, electrical safety notices, maintenance instructions and pre-specified material kits. The system is available both on CD-Rom, via Internet and in paper format (manuals) as well as in MS Exel spreadsheets. It has been estimated that the overall cost reduction by using this rational system has been more than 50% over the last decades. A suggestion is therefore to introduce a similar system for low-cost rural electrification in Sub-Sahara.

Locally obtained alternative material and components

To further lower costs in rural electrification many components could be obtained locally. This is especially true when it comes to poles and some of the pole-top assembles. As poles contribute to the cost by up to 20-30% or even more in case of high transportation cost, the local supply of pole material is a critical factor that could help lowering cost for rural electrification. It is supposed that any rural electrification program should investigate alternative pole manufacturing sources, close to the project sites.

Consumer involvement in reducing costs

As installation of rural electrification systems are based on lower cost material the proportion of the labor costs increases. Typically for a MV or LV network the labor cost can be between 20-30 %. Involving the consumer could lower cost further in many cases. As the consumer has to take care of internal installation other cost reducing methods could also be looked into. One example is the local contribution of material and labor. In many rural settings the contribution to installment of e.g. drop-wires and any ground work as digging cable trenches, building transformer houses etc. could be in kind contributions that boils down the network installation costs to minimum.

A proposed strategy to introduce low-cost rural electrification

Feeding LV customer with 1 kV cable connection

Calculation has been made which possible lengths 1 kV cables can be used too feed small loads as e.g households, houses with battery charges etc. A fuse to protect the cable is needed. The feeding voltage is assumed 230 volts and voltage at the load is at least 180 volts. Surrounding temperature is 20°C. No voltages drop in the fault location. Loads characteristics is CosFi=1.

The breaker should have an A-characteristic curve. This breaker shall accept maximum 2-3 x In.

The calculation below gives longest lengths under best conditions.

Cost effective electrical networks