Mechanical Design
The mechanical design of a SWER line can lower its lifetime cost and increase its safety.
Since the line is high voltage, with small currents, the conductor used in historic SWER lines was No. 8 galvanized steel fence wire. More modern installations use specially-designed AS1222.1 high-carbon steel, aluminum-clad wires. Aluminum clad wires corrode in coastal areas, but are otherwise more suitable. Because of the long spans and high mechanical tensions, vibration from wind can cause damage to the wires. Modern systems install spiral vibration dampers on the wires.
Insulators are often porcelain because polymers are prone to damage from ultraviolet. Some utilities install higher-voltage insulators so the line can be easily upgraded to carry more power. For example 12kV lines may be insulated to 22kV, or 19kV lines to 33kV.
Reinforced concrete poles have been traditionally used in SWER lines because of their low cost, low maintenance, and resistance to water damage, termites and fungi. Local labor can produce them in most areas, further lowering costs. In New Zealand, metal poles are common (often being former rails from a railway line). Wooden poles are acceptable. In Mozambique, poles had to be 12m to permit safe passage of giraffes. If an area is prone to lightning, modern designs place lightning ground straps in the poles when the poles are constructed, before erection. The straps and wiring can be arranged to be a low-cost lightning arrestor with rounded edges to avoid attracting a lightning strike.
Read more about this topic: Single-wire Earth Return
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