Transposition Tower for Overhead Electrical Transmission Lines

Transposition Tower


What is Transposition Tower?

The basic definition for transposition of the transmission line is to rotate the conductors which result in the conductor or a phase being moved to the next.

In electrical power transmission, a transposition tower is a transmission tower that changes the relative physical positions of the conductors of a transmission line. A transposition tower allows these sections to be connected together while maintaining adequate clearance for the conductors.

What is the purpose of the transposition tower?

The transposing is necessary as there is the capacitance between conductors, as well as between conductors and ground. 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.

What is the suitable distance for transposing in transmission lines?

Ensuring a good transposing of a three-phase system, the transposing is applied after each (1/3n) distance of the line. Where n is the number of transpositions across each line length.

(1/3)distance to get equal average reactances(XA=XB=XC) overall distance of transmission line and then the symmetric system.

For single-circuit lines, you can get a balanced operation if you transposed for each 1/3 of the overall distance. This statement, however, is only valid if you did not tap (load) the line anywhere along its length except at the end.

For double-circuit lines, you can either transpose both circuits at 1/3 of the line length or transpose one circuit at 1/6 of the line length, yet, surprising as it may seem, this will achieve balanced voltage the line ends.

What are the advantages and disadvantages of transposition?

There are actually no disadvantages in power line transposition system, but some advantages are as below:
  1. When conductors are not transposed at regular intervals, the inductance and capacitance of the conductors will not be equal.
  2. When conductors such as telephone lines are run in parallel to transmission lines, there is a possibility of high voltages induced in the telephone lines. This can result in acoustic shock or noise. Transposition greatly reduces this undesired phenomenon.
  3. In practice, however, conductors are not transposed in the transmission lines. The transposition is done in the switching stations and the substations.
A transposition tower is important to allow transposition sections to be connected together while maintaining adequate clearance for the conductors. 


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