Maximum Transmission Line Span

[NAZ55]

Is there a code or requirement depicting how long a transmission span can be?

In particular for a 345kV tranmission line?

 

[jghrist]

Not in the USA, as long as strength and clearance requirements are met and due consideration is made to aeolian vibration concerns.

 

[NAZ55]

jghrist,

Just to clarify, you are referring to the span and not the transmission line length itself. Correct?

My question was regarding the span between two supports and how far can a transmission span go without requiring another support.

 

[davidbeach]

Yeah, I'm sure that's what he meant. I've seen spans in excess of a mile, but not very often. 1/5 to 1/4 mile spans are not uncommon, but it all depends on site conditions.

 

[jghrist]

Right. Span lengths of river crossings can get very large. Also in the mountains across valleys.

 

[davidbeach]

http://maps.google.com/maps?ll=48.516016,-123.54032&z=16&t=h&hl=en

is a 3300+ foot crossing.

http://maps.google.com/maps?ll=45.626453,-120.9089&z=16&t=h&hl=en

is a 4100+ foot crossing. I'm sure I've seen longer, and I've read about one in excess of 8000 feet.

 

[stevenal]

Here's one that I found impressive from the ferry:

http://maps.google.com/maps?ll=48.516016,-123.54032&z=16&t=h&hl=en

The two lines are invisible, but join the visible rights of way. One line makes a 90 degree turn up hill prior to crossing. The other crosses much lower without turning north first. Equivalent height mid-span, conductor size, and towers. I'm guessing the lower line may be using one of the new low sag cores. From the scale, it looks like it exceeds 8000.

 

[davidbeach]

Steven, your link is the same as my first link, a bit over 3300 ft. Probably not what you meant to post.

 

[stevenal]

Yeah, copying and pasting from address bar doesn't work very well. Try

http://maps.google.com/maps?ie=UTF8&hl=en&ll=49.768072,-124.134436&spn=0.040801,0.094585&t=h&z=14

Confirmed this time.

 

[davidbeach]

Nice. Measuring it in Google Earth it is over 10,300ft for the east span. Zooming in in Google Earth, you can see the conductors; two circuits, individual towers for each conductor, 75ft spacing between phases, and lots of marker balls on the spans.

 

[NAZ55]

Wow! pretty cool!

Only us engineers would find it to be cool

 

[bacon4life]

Looks like 17,638 ft is doable.

http://en.wikipedia.org/wiki/Ameralik_Span

When we recently replace a 6200ft span, the only electrical code requirement that caused us grief was the NESC conductor tension limit of 25% rated tensile strength. The limit is a decent rule of thumb to prevent vibration damage in typical spans. Although we had an extensive damper system designed, we ended up having to use a stronger cable just to meet the NESC requirement.

http://www.ci.tacoma.wa.us/power/towertalk/Images/Historicals/pictur16.jpg

 

[BJC]

Greenland. This on is 5,376 Meters long.
What do they do with all that power in Greenland. There must be a mine some where nearby.

http://en.wikipedia.org/wiki/Ameralik_Span