www.emfs.info/Source_transmission.aspThe field also depends on the relative phasing of the two circuits (see the figure below). A few lines have "untransposed" phasing, with the phases in the same order from top to bottom on the two sides of the towers. This produces a field which falls as the inverse square of distance from the line. However most lines have "transposed" phasing, with the opposite order of the phases on one side to the other. This introduces an extra degree of symmetry and extra cancellation between the fields from equal currents on the two sides; the resultant field falls more nearly as the inverse cube of distance, producing a much lower field at large distances from the line.
Scott35, Foof, What sort of thing is that?. Bjarney, Is this sort of thing peculiar to the US?, as I have never seen a thing like this before in NZ or in Australia?. Also Bjarn, how is this thing operated?.
Let's face it, these days if you're not young, you're old - Red Green
#116128 - 02/20/0402:02 PMRe: Lineworkers: What's the correct term for this Animal?
Trumpy — Transpositions would be more likely found on longer lines, which are by default transmission voltages.
Another way of looking at it would be to imagine ‘phase rolling,’ and that a dual-circuit line may have one set of 3 conductors twisted clockwise and one twisted counter-clockwise at a transposition point. In Scott35’s pic, though, it looks like both circuits roll in the same direction.
The purpose is to balance phase-to-ground and limit circuit-to-circuit reactances, which helps in voltage balance, makes it easier to sense line-to-ground faults and less susceptible to mutual coupling, which can cause sympathetic line tripping—where two adjacent circuits both trip with one circuit faulted and one healthy.