|This article does not cite any references or sources. (May 2012)|
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. A transposition tower allows these sections to be connected together, while maintaining adequate clearance for the conductors.
This is important since it balances electrical impedances between phases of a circuit.