- Joined Sep 22, 2013
Why do high tension/voltage power lines droop when under heavy loads?
Interesting. Do you think the no\umber of atoms in diameter or length changes? Resistance is a matter of number of atoms, isn't it?Because the wires get warmer due to I²R losses and this causes thermal expansion of the metal wire, making the wires longer and causing more droop.
Well, the answer does not require any change in resistance, only a change in temperature due to resistive heating, leading to a decreased density and thus an increased length.
I think most of the large spans here are steel reinforced.Aren't main power feed lines made of aluminum wire ??
Obviously, if the wire expands due to heat, then the number of atoms per unit volume must decrease, since there are a fixed number of atoms involved.
The wire material is not really important to this discussion since virtually all metals expand when heated.I think most of the large spans here are steel reinforced.
The question was about if the cables were Aluminium.The wire material is not really important to this discussion since virtually all metals expand when heated.
Steel is higher strength than aluminium which allows for increased mechanical tension to be applied on the conductor. Steel also has lower elastic and inelastic deformation (permanent elongation) due to mechanical loading (e.g. wind and ice) as well as a lower coefficient of thermal expansion under current loading. These properties allow ACSR to sag significantly less than all-aluminium conductors.
I mean the cable material is not pertinent to the OP's question.The question was about if the cables were Aluminium.
Yes, most common metals increase resistance with temperature.Yes, some wire changes resistance when heated, like tungsten, especially. Does aluminum or copper change resistance notably in this instance? I guess any change effects voltage drop in this instance, doesn't it.
Thanks for that observation. Yes, that was the way I originally read the post.Oh, I think I see the problem. We believe the original question was about the physical drooping of hot wires, and not about any drop in voltage. hp1729 appears to be talking about resistance and voltage sag, another type of droop?
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by Jake Hertz
by Jake Hertz
by Jake Hertz