Swapping phases on HV power line

Others in this newsgroup are in the business and more knowlegable than me, but I'll take a shot at this.

What you probably saw was a transposition tower that was indeed there to swap the positions of the A-B-C phases. I believe that this will equalize the electrical characteristics of (inductance and capacitance) of the three conductors relative to each other as these characteristics are based in part by the position each conductor occupies on the crossarm.

Movie Trivia - In the 1937 lineman movie "Slim", experienced lineman Pat O'brien says to journeyman lineman Henry Fonda.... "So now you'll know what to do if you ever run into a transposition tower"...(paraprhased)

Beachcomber

Beach

Transposition also lowers the interference induced in adjoining lines. With fiber optics and the like on long runs replacing traditional open telephone lines, the need for reduced interference is becoming less important. Transposition, as indicated above, might still be needed so that each phase sees the same average environment to retain balance.

Bill

-- Fermez le Bush

configuration

Yes you are right

| On Fri, 15 Sep 2006 02:14:29 +0000 (UTC), | snipped-for-privacy@world.std.spaamtrap.com (Michael Moroney) wrote: | |>Idle curiosity... |>

|>I was driving by/under some power lines and noticed an odd configuration |>on one set of poles. The next time I went by I took a closer look. |>This line is of the type with two poles, a large crossarm between them |>and the 3 phases in a line, two hung from the ends of the crossarm and |>the third hung from the middle of the crossarm between the poles. I'm |>guessing somewhere around 110 kv. |>

|>At the odd location there were 3 poles with no crossarm. Here, the 3 |>phase wires swapped positions. By this I mean the left wire south of |>there was connected to the center wire north of there, the center wire |>south of there was connected to the rightmost wire north of there and the |>rightmost wire was connected to the left wire. |>

|>Why was this considered necessary/helpful? This swap was near a tap for a |>small substation if this makes any difference. | | Others in this newsgroup are in the business and more knowlegable than | me, but I'll take a shot at this. | | What you probably saw was a transposition tower that was indeed there | to swap the positions of the A-B-C phases. I believe that this will | equalize the electrical characteristics of (inductance and | capacitance) of the three conductors relative to each other as these | characteristics are based in part by the position each conductor | occupies on the crossarm.

I once saw a MV distribution circuit in a rural area of WV that had what appeared to be almost continuous transposition. Each pole had a crossarm structure that looked like a sideways "Y". Each arm carried one conductor. The top of the pole had a thin wire that I assumed was the ground wire. Every other pole had the "Y" crossarm turned the opposite way so that on even poles the open side of the "Y" faced the side of the road and on odd poles it faced away from the road. The wires rotated such that the wire that was on the solo (bottom of Y) end on one pole went to the lower half of the open end on the next pole. Then on the 3rd pole it would across over sideways and end up on the lower half of the open end of the Y facing the other direction. On the 4th pole it would then move up to the single end of the Y. On the 5th pole it would move to an upper arm and the for the 6th pole cross over to the other side. Finally, the 7th pole was the same as the 1st. The other 2 phases were rotating right along with this. It ran like this for a few miles, with occaisional transformers tapping in to serve an occaisional home. I do not recall if these were L-L or L-N connections. That was about 40 years ago.

Transposition will balance the line impedances but originally it also was to reduce coupling to adjacent circuits, particularly communication circuits. If you look at older multiwire telegraph lines, you will see that these are transposed. transposition of a kind is also used in telephone cables to minimise crosstalk. EHV power lines are often not transposed although unbalanced line impedances do occur

- too expensive and far enough from other circuits as to not cause problems

| Transposition will balance the line impedances but originally it also was to | reduce coupling to adjacent circuits, particularly communication circuits. | If you look at older multiwire telegraph lines, you will see that these are | transposed. transposition of a kind is also used in telephone cables to | minimise crosstalk. | EHV power lines are often not transposed although unbalanced line impedances | do occur | - too expensive and far enough from other circuits as to not cause problems

That's how we're able to couple into the big power lines and steal some electricity :-)