Force of a 220kV Cable falling

[Chadwick]

TL;DR Summary

How would you calculate the force at a point of a falling 220kV Conductor?

Summary: How would you calculate the force at a point of a falling 220kV Conductor?

Hi, bit a of a funny one.
I need to calculate the force of a cable falling at a point (left edge of a scaffold) as detailed in the attached sketch. (Not to scale what so ever).
We’re building a scaffold between two towers to protect a railway. It needs to withstand at least 1 cable falling, if it were to fall it would release at the tower, I would consider whichever the worst case would be at.

Considering the worst case scenario what would the force be on the scaffold?

Now it would be simple if we treat the cable as a solid, but since it is a cable how would this affect the fall?
I imagine the whole weight of the cable would not be landing on the scaffold, some weight would be taken by the tower and possibly the ground.

Any help you can give would be appreciated!

 

[anorlunda]

Wow. Tough question. I moved it to ME because it appears that the electricity plays no role.

How paranoid worst case do you need? I'm wondering of the end of the cable can snap like a bull whip.

 

[Chadwick]

Thanks for that!

Hard question when you're trying to balance over engineering and costs haha.
If our aim is to protect the railway we might be okay with assuming that the whip would occuur at the ends, far enough from the scaffold.Also, appologies, forgot to include a fairly crucial element to the problem.

Failure could potentially occur at when transferring a cable from one tower to the other, or when sagging the cable, this would introduce horizontal forces onto the cable which would impact the fall of the cable.

In transferring the winches would exert roughly 2.7t (27kN) horizontally onto the cable, when sagging a design 3.7t (37kN) would be applied.

In case it wasn't complicated enough :)

 

[Baluncore]

When a cable breaks it will probably be at the support point where there is an acoustic impedance mismatch.

The end where the break occurs will not start to fall until tension in the cable has been relieved. That involves the speed of a tension wave in the cable. The cable will not drop flat on the ground across your scaffold, it will be propelled toward the remaining attached tower by cable tension. It will coil, kink and tangle before it reaches the ground. The scaffold will need a mesh that prevents loops of cable falling through to obstruct the track.

Wind force on a cable during a wind storm is often greater than gravity, so you can expect the cable to fall sideways by more than one pylon height. I have found antenna elements 3 times further from the tower than the antenna height, some have not yet been found.

Ice buildup will change the game when lengths of ice fall on the tracks. Ice will increase windage, but will reduce the problem of stored energy in the tension.