Why transmission lines / wires become loose after installation

[mqasim33]

When we install transmission lines / wires, after some days these become loose. Why??

 

[FvM]

"install transmission lines" means specifically?

 

[albert22]

May be you are talking about losses? Meaning that power is lost.
I dont know what type of transmission line you mean. Or how many days. But coaxials can get water inside if they are not correctly sealed at their ends. Corrosion or water at the connectors gives problems too.
Parallel transmission lines are very sensitive to nearby objects.
Sharp bends or squeezing can also produce losses.

 

[dick_freebird]

If you try to pull them dead tight, that's a lot of longitudinal
force (1/sin(0) multiplies the cable weight, at the ends -
zero being the initial sag-angle). So you get plastic
deformation of the copper, which is fairly soft, thus stretch.

 

[tpetar]

Maybe just some squirel playing around. :smile:

Can we get additional informations about type of cables, installation way, and something about transmited type of data and conditions when link is lost?

 

[mqasim33]

I mean power transmission lines. After some period of time their length is increased and they become loose. Why their length increases. If it's due to heat losses then why they didn't tight after becomoing cold???

 

[tpetar]

Post cable specification - datasheet of cables.

Did you check certification of cables?

Indoor / Outdoor, UV pretected.....

You didnt say any relevant data about cable, except that is power cable, and based on posted informations I think even manufacturer cant help you.

- - - Updated - - -

Maybe you use wrong cable for your needs.

 

[chuckey]

You say power cables extend with age and droop?. I have never heard of this , both Cu and Al work harden under flexing and become brittle and subject to fracture. So a Cu or Al cable that swings about in the wind will fail eventually.
Frank

 

[FvM]

Although the OP finally revealed that he's talking about overhead power lines, the information is still vague. The thread is more like a guessing game.

 

[albert22]

Just guessing: Beside deformation of the Cu . The individual wires that make the cable may come together more closely with the tension. Similar to stretching a rope.

 

[chuckey]

Youngs modulus says that for a small deformation , metals act like a spring. So your piece of cable when erected will extend in length and if you lay it on the ground it should shrink back to its natural length. Similarily for when its hot, it extends and then should shrink when it cools.
Both Cu and Al work harden so you never get springs made of these metals. Al has a fatigue limited life, thats why aircraft are stripped down and inspected because the airframe extends/contracts and vibrates a lot, so the Al can fracture due to the work hardening. Steel bridges are not stripped down because they don't fail like this, though they do rust :-(
Frank