Cables between pylons always dip but surely a lot of money could be saved if they were pulled taut.
In: Engineering
Any rope or wire of any material that stretches to any amount will have some sag in them. You would need a materai that do not stretch in any way to have a straight wire but not material like that exist.
So all wires will have some slack and the amount depend on the length between the pylons and the amount tension and strength of the wire. The strength and mass of the wire is also very important.
You also need margins so the force of the wind or even ice that form on the cables will not result in a cable tha
So the design is a composite between strength of the materia vs the cost and the cost of the pylons.
Use the calculator at [http://eguruchela.com/math/Calculator/cable-sag-error](http://eguruchela.com/math/Calculator/cable-sag-error) and 300 feet length, 32 ft/s^2 in force perpendicular. With a wire from [https://www.engineeringtoolbox.com/wire-rope-strength-d_1518.html](https://www.engineeringtoolbox.com/wire-rope-strength-d_1518.html) take a 1/4 inch wire with a mass of 0.11lb/ft.
If you use the Minimum Breaking Strength of 5480 lb_f the sag is 7 feet and you use a extra 0.4 feet wire. If you use more force you cant be sure that it will hold and you haven’t margin for wind
At Safe Load of 1100 lb_f the sag is 35 feet and the wire is 11 feet longer (3%)
The number are for steel wires but they are bad conductor. So power lines use Aluminium-conductor steel-reinforced cable that have lower strength compared to mass so you will have more sag. If you add more steel the wire can have less sag but cost more so you optimize cost vs extra cable needed and we get what is used.
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