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Why phases in transmission line are transposed

There are usually 3 separate Phases plus a Neutral in a transmission line which is part of a “Power Distribution Network”.

Electrical power is commonly generated at a power generation station in three separate “phases”. The “Hots” (“Live” wires in European parlance) of each of the phases are timed to “lag” each other in wave/cycle terms as follows: the Hot of the first phase is generated at 0o (Zero degrees, which is equivalent to 360o), the Hot of the 2nd phase is timed to lag the Hot of the the first phase by 120o and the Hot of the third phase is timed to lag the Hot of the first phase by 240o.

What exactly do you mean by “Transposed” in relation to the phases?

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I am sorry but i am not totally satisfied with the ans
” the Xline tends to show variation in voltage and freq. from time to time
to avoid this the phases are interchanged

if A B C are the 3 phases the interchanging will look like below
1st position
2nd position
3rd Position
i.e only the positions of phases are changed the distance between them remains the same all the time


There may be (telephone etc..) communication lines running in parallel with the transmission lines, and these comm lines may get affected by the inductance of Xmission lines (magnetic interference) leading to poor reception quality. In order to improve the same, lines r transposed as in this case the total voltage drop (due 2 inductance) gets nullified every complete cycle of transposed lines. Generally, lines r transposed at switching stations and not midway, or the communication lines r themselves transposed to cancel the overall effect. -SHIVESH KR YADAV

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