Mozambique is a Southern African Country with a Population of 19 Million and a land area of some 800,000 sq km (30,882 sq miles). The majority of the population lives in rural areas, surviving on subsistence agriculture, fishing and hunting. Despite making significant progress during the last 15 years, Mozambique is one of the world's poorest countries, ranked 172 of 178 countries in 2007. At present, the electrification ratio is around 20% in urban areas, but less than 2% in rural areas, with an overall energy use per capita of 89.5 kWh per annum in 2006.

DEVELOPMENT CHALLENGES

The National Grid has been extended since Electricidade de Moçambique was created in 1977. EdM has an electrification master plan to provide conventional three-phase technology to supply the major cities. For rural areas, electrification poses financial and economic challenges due to the very low load density and the need to supply customers without the means to afford energy. These problems are common for utilities around the world, particularly in developing countries. Therefore, in order to provide grid-connected electricity to rural areas, it is necessary to:

• Minimise investment costs.

• Minimise maintenance and operational costs.

• Simplify design, equipment specifications and procurement.

• Establish transparent methods for system management and customer billing and account collection.

These principles form the basis of the international response and launch of Low Cost Rural Electrification programmes. One of the most frequently used forms of LCRE is a technology known as Single Wire Earth Return (SWER) that is also used in Australia, New Zealand, Canada, the United States (Alaska), South Africa, Burkina Faso, Botswana and Namibia.

EdM is currently implementing two Danish Aid-funded SWER systems to supply Mavila and Morrungula, both in the Inhambane province. This project is taking advantage of the experience of neighbouring countries, namely South Africa and Namibia, in the form of reviewing and adapting engineering standards.

SWER TECHNOLOGY

The SWER distribution system uses the ground for the return path. This system is easy to construct and maintain, and is very economic overall. Often regarded as a marginal technology in Australia, SWER is a mainstream technology with some 200,000 km (124,274 miles) operating at 19.1 kV or 12.7 kV in seven states. In Mozambique, they decided to construct 19.1-kV SWER line spurs from the existing 33-kV three-phase overhead lines in rural areas as the first stage of the electrification programme.

The key components of the SWER distribution system are the poles or conductor supports, conductors and insulators. For the most economic system, it is necessary to optimise the procurement of materials and construction methods. The options available to the system designer include:

• Poles

  The conductor supports commonly used include wood poles, steel poles, pre-cast, pre-stressed and spun-concrete supports. In Mozambique and South Africa, there is a thriving wood pole industry using plantation timber, which results in the availability of low-cost, quality treated poles. Wood poles are very robust, can withstand transport and are the product of choice.

• Insulators

  The available options considered include post or pin insulators for in-line and small angle sections. Since polymer insulators suffer ultraviolet damage in general, porcelain insulators are used in Africa. Standard insulators used for 12.7-kV and 19.1-kV SWER projects are rated at 22 kV and 33 kV, because they offer the opportunity for future upgrading.

• Conductors

  In the past, No. 8 galvanised fencing wire was a common choice for SWER conductor, but more suitable conductors are now manufactured (for example, galvanised steel conductors to AS1222.1 and aluminium-clad steel conductors available from manufacturers such as Olex are used in Australia). For economic reasons, Bantam (13.1 kcmil, ¾ ACSR, 5.04 mm [0.2 inches]) or Magpie (20.87 kcmil, ¾ ACSR, 6.36 mm [0.25 inches]) conductors, which have separate outer cores of aluminium and steel inner cores, are used in Africa. As long as they are not erected in coastal areas, corrosion is not a problem.

• Vibration damage

  To minimise line construction costs, SWER is designed with long spans (for example, 300 m [984 ft]) on a level terrain, based on the use of 12-m (40-ft) poles. Even longer spans may be used in undulating country. The conductors have to be strung at a higher tension, which can create damage due to conductor vibration. The use of spiral vibration dampers, retrofitted to existing line, with armour rods and preformed ties on new construction, has largely overcome this problem. An alternative solution is to use suspension insulators on the longer spans.