Swapping phases on HV power line

[Michael Moroney]

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.

 

[Beachcomber]

On Fri, 15 Sep 2006 02:14:29 +0000 (UTC),

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.

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

 

[[email protected]]

| On Fri, 15 Sep 2006 02:14:29 +0000 (UTC),
| [email protected] (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.

 

[Don Kelly]

| On Fri, 15 Sep 2006 02:14:29 +0000 (UTC),
| [email protected] (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.

--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below
|
| first name lower case at ipal.net / [email protected]
|
|------------------------------------/-------------------------------------|

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

 

[[email protected]]

| 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