High Tension Power Line - Max Pull Angle

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schneider

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My question has to pertain to the construction of a 345 kv overhead transmission line.

I am working on designing the the Wire Pull/tension site areas to pull the 345 kv transmission line. My splicing sites are are a max of two miles apart.

I was wondering max angle the transmission line can change over a two mile strech at one tower location before needing to place a wire pulling/tension area?

Does this angle increase or reduce due to steep terrian as well?

Thanks - I figure some line men should know
 

mivey

Senior Member
I was wondering max angle the transmission line can change over a two mile strech at one tower location before needing to place a wire pulling/tension area?
You would need to calculate the sheave load at the critical points for your particular case. In a straight level pull, the conditions at the ends will be the worst case points. For angles and inclines, they could become critical, more-so if at the end of the pull (due to traveler efficiency). If you pull through a dead-end greater than 30? you would use two travelers and maybe four if the angle is over 50?.

Using a larger diameter sheave also helps as you reduce the amount the cable has to bend and thus increase the traveler efficiency. You might normally assume a 5% tension increase at a traveler but with a diameter over 20x the conductor diameter it might be as low as 2%.

A critical calculation would be the bearing pressure at the sheaves because excessive force will either damage the conductor or the sheave lining or maybe even over-load the traveler as a whole.

See the IEEE Std 524 Appendix for calculation info.

Does this angle increase or reduce due to steep terrian as well?
Steep terrain also increases the stress.
 
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