Aluminum has become the material of choice for overhead transmission lines, surpassing copper due to its abundance and cost-effectiveness. The most prevalent type is the aluminum conductor, steel-reinforced (ACSR), which combines aluminum strands around a steel core. Other variants include all-aluminum conductors (AAC), all-aluminum alloy conductors (AAAC), aluminum conductor alloy-reinforced (ACAR), and aluminum-clad steel conductors. Advanced designs, such as aluminum conductors with steel support and gap-type ZT-aluminum conductors, can operate at temperatures exceeding 150 degrees Celsius.
The electrical design of transmission lines involves several critical factors. These include the type and size of the conductor, the number of bundles per phase, and the thermal capacity of the conductors. Voltage gradient control is essential for minimizing energy losses. Insulator discs, which are placed between the conductors and the support structures, are used to ensure adequate insulation. Proper clearance and line insulation are vital for safety and efficiency. Shield wires are placed strategically, intercepting lightning strikes to reduce tower footing resistance and protect the transmission lines.
Transmission lines operating above 69 kilovolts (kV) typically employ suspension-type insulators, which consist of strings of porcelain, toughened glass, or polymer discs. The support structures vary based on voltage levels, with self-supporting lattice steel towers used for high-voltage lines, and wooden frames for lower-voltage applications. Shield wires, usually made from high-strength steel or Alumoweld, protect against lightning and are properly grounded to ensure safety.
The mechanical design ensures the strength and durability of conductors, insulator strings, and support structures. Environmental considerations are also crucial, encompassing land usage and visual impact. The goal is to achieve an optimal line design that meets all technical criteria while minimizing costs, considering installation expenses and operational losses.
