Engineering:Transposition tower

In electrical power transmission, a transposition tower is a transmission tower that changes the relative physical positions of the conductors of a transmission line in a Polyphase system. A transposition tower allows these sections to be connected together, while maintaining adequate clearance for the conductors. This is important since it distributes electrical impedances between phases of a circuit over time, reducing the problem of one conductor carrying more current than others.

Double-circuit lines are usually set up with conductors of the same phase placed opposite each other. This reduces the reactance due to mutual inductance; the reactance of both circuits together is less than half that of one circuit. For example, a section of a line may be (top-to-bottom) phases A-B-C on the left, also phases C'-B'-A' on the right. The next section may be B-C-A on the left, also A'-C'-B' on the right. Therefore, the rotation on each side of the tower will be opposite.

Here, on the right the phases are rotated; on the left, two phases are swapped, thus the rotation sense changed.
Transposition tower. On the right side, the phases are rotated upward, on the left side downward.
Transposition by using elongated traverses
Transposition on a single-phase line
Transposition by using multiple towers
Transposition in the span field of a 420 kV-line in Sweden