Grid connection
Practical Action
Africa. The main disadvantage is that SWER lines tend to be long, with high impedance,
so the voltage drop along the line is often a problem, causing poor power quality.
The Box below describes one approach to low-cost rural electrification which worked for Tunisia.
Low-cost options must be considered for suitability for each location.
Tunisia’s Low Cost Electricity Distribution System
One key reason for cost reductions in Tunisia’s successful rural electrification programme was
the early adoption, in the mid-1970s, of a low-cost, three-phase/single-phase distribution
system, known as MALT.
Unlike most African countries and many other developing countries, Tunisia chose not to
adopt the technical standards it had inherited from Europe, which included a three-phase, LV
distribution system, suited to densely populated areas and heavy loads. Many developing
countries that did adopt this system, ended up with a high-cost-per-km distribution
infrastructure that was poorly suited to their scattered settlements and low demand levels.
Tunisia’s decision to adapt the lower-cost, three-phase/single-phase distribution
technology used in North America and Australia to its unique environment is arguably
the single most important reason for the country’s later success in rural electrification.
The three-phase/one-phase MALT distribution system adopted in Tunisia consists of major
arteries of overhead lines in three-phase, 30-kV, line-to-line voltage, with four conductors
(three phases and one neutral wire) and secondary, single-phase, 17.32-kV, line-to-neutral
voltage rural distribution overhead lines (two wires: one phase and one neutral). Single-phase
transformers give a secondary, phase-to-neutral voltage of 230V (single -phase, LV lines),
which is used by most rural customers. The distribution system is composed of robust
materials and equipment that are easy to use and maintain.
When Tunisia adopted the MALT system, it made a second key technical decision: opting for
a relatively high, single-phase 17.32-kV voltage, rather than the weak 3 or 5 kV of the North
American model. The higher voltage was selected for the single-phase rural electrification
overhead lines because of the long distances between villages and the nearest three-phase
artery and to provide for future demand growth over the 30-year lifetime of the lines.
Source: Low Cost Electricity and Multi-Sector Development in Rural Tunisia:
Important Lessons from the Tunisian Success Story, 2004
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