sag-tension design for twin conductor

[ronaldgapuz]

hello all...

i just want to ask how you design sag-tension calculation for twin-conductors (2 conductor per phase) [and also quad-conductor]. i only have experience in single-conductor per phase arrangement and i am thinking there might be other design parameter(s) to be considered like doubling(???) the conductor weight, etc. for determination of sag and tension.

i am new in OHL design. please help me... thank you all in advance.

 

[Skogsgurra]

Hi Ronald,

I am not even new to Overhead Line design - I haven't even started...

But if you think about it, you will realise that you can hang one conductor between two poles and there it is. If you hang an identical conductor same fashion between same points, it will be parallel and close to the first one. Now, if you connect those conductors mechanically (and electrically) with transversal links, there will be no electrical or mechanical difference between the connecting points. Neither before you connect the links nor after you have connected them. So each conductor carries its own load - mechanically and electrically and there's no need to change the design. The sag will be the same for both when hot and they will both shrink the same amount when cold.

But, of course, you need stronger poles and stronger insulator chains to support a twin or quadruple set of conductors. But that's not what you asked about - or is it?

Gunnar Englund

http://www.gke.org

 

[ronaldgapuz]

thanks Mr. Gunnar, for your reply.

i was thinking that because there are two conductors, i have to consider doubling the conductor weight. if i have understood your reply correctly, then there's no need to change any of the design parameter on getting the sag and tension and go on with my computation as if it's a single conductor line.

thanks again and good day.

 

[stevenal]

Please don't forget about the connecting bars when doing your calculations. If frequently spaced and spans are long, they may have an effect on sag, especially if coated with ice. Depending on orientation, they may have an effect on the wind loading also.

 

[jghrist]

I agree. There is no difference in sag-tension calcs for bundled conductors vs single conductors except for the probably negligible weight of the spacers.

 

[tinfoil]

Talk to the manufacturers of your conductors. They should have fairly precise specs for sag/tension / max tension performance of their double conductor.

But I agree that the sags should be virtually indistinguishable from two separate free-hanging conductors, except that the amount of ice deposited on a non-cylinder (and the resulting weight and wind-drag) will NOT be double that of a cylinder.

 

[stevenal]

NESC 251Ab: "On bundled conductors, the coating of ice shall be considered as individual hollow cylinders
around each subconductor."

 

[tinfoil]

Are we talking about high-voltage 'bundled' conductors (i.e. 345kV, with SPACERS, or specialty twin conductors, like on this link?

http://www.sural.com/products/bare/t2.htm

 

[ronaldgapuz]

mr. tinfoil, my project is for a 230kV OHL with 2 spearate conductors running parallel to each other per phase.

ice is not a consideration since i am working in the mid-east.

i'd like to thank everybody for the replies. it sure really is a big help finding this forum. thanks again.