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Conductor sag and tension

Conductor sag and tension

Conductor sag and tension


I dont know the procedure in calculating conductor sag and tension of a new transmission line, could anybody help.

Is there any criteria on selecting what sag(on the sag tension table) will be used in determining the height of the transmission tower?

RE: Conductor sag and tension

What I mean is how do they calculate the sag and tension of a new trasnsmission line, 230 KV, with a ruling span of 1000ft and a maximum wind velocity of 200 KPH.

I want to calculate it by hand (using spreadsheet).

RE: Conductor sag and tension

See if you can get this book it as all you require:-



ISBN 0 340 147717

Its to complicated to go into here as you need also to consider ice on the line in addition to wind and also in hot weather how much more sag and tension will occur from the initial installation tension.


RE: Conductor sag and tension

K, thanks a lot guys for such help. I learned a lot with those references you gave. May God bless everyone.

RE: Conductor sag and tension

If you are in the T-Line business your company should consider PLS-CADD which is probably used by the majority of companies in the industry.  SAG10 now by Southwire and formerly sold by ALCOA is the standard for sag and tension calculations where regular creep and elevated temperature creep is considered.  ALCOA has many years worth of creep data used for finding the sag either before or after a wire has been loaded by a wind or ice event.  There is also a PLS-CADD Lite where you can look at a single structure for a much cheaper price from Power Line Systems.

I have been called "A storehouse of worthless information" many times.

RE: Conductor sag and tension

Tower height is decided this way:

1.You calculate the max.sag at basic span to get the height of the bottom crossarm height, you need to consider the electrical clearance to the ground as well.

2.You decide the vertical phase spacing and earthwire to uppermost phase distance which you may follow the relevant code and local practice.

RE: Conductor sag and tension

Max Sag occurs at max. temp. in most cases. You need to work out the max. sag from other cases such as wind or icing in which the conductor tension reaches the max. tension. Max. tension is limited to UTS/F.O.S, sometimes EDS may become a critical factor when you calculate the sag-tension.

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