Single-circuit transmission line
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A single-circuit transmission line is a transmission line where one circuit is carried on a tower line.
For a three-phase system, this implies that each tower supports and insulates three conductors.
[edit] Construction
For a single wood pole structure, a pole is placed in the ground, then three crossarms extend from this, either staggered or all to one side. The insulators are attached to the crossarms.
For an "H"-type wood pole structure, two poles are placed in the ground, then a crossbar is placed on top of these, extending to both sides. The insulators are attached at the ends and in the middle.
For a lattice tower structure, there are two common forms.
One has a pyramidal base, then a vertical section, where three crossarms extend out, typically staggered. The insulators are attached to the crossarms.
Another has a pyramidal base, which extends to four support points. On top of this a horizontal truss-like structure is placed. The insulators are attached to this.
Steel pole structures follow the wood pole structures in an obvious way.
In all cases, there are usually one or two ground wires attached to the top of the poles or towers.
