Sag & Tension Calculation 1

[MIGMIG]

Hi;
As you know for calculation of sag & Tension, wire between spans should follow the sagittal curve. but I want to calculate the sag & tension wire between termnations' equipment in the power substation. In some spans the shape of wire is like s and it means that wire does not follow the sagittal curve. Now I want to know that how can I calculate the sag tension of these spans.
Thanks.

 

[jghrist]

Do you mean "catenary"? I never heard of "sagittal" being used for conductor sag.

Main Entry: sag·it·tal
Pronunciation: \?saj-?t-?l\
Function: adjective
1 : of, relating to, or being the sagittal suture of the skull
2 : of, relating to, situated in, or being the median plane of the body or any plane parallel to it <a sagittal section dividing the body into unequal right and left parts>
—sag·it·tal·ly adverb

If the conductor in the substation is shaped like an "S", then there is not enough tension to pull out the curve from when the conductor was on the reel. There's no way to calculate this.

 

[bacon4life]

IEEE Std 1527-2006 has some test results from Hydro Quebec on how the wire sags in various types of short substation spans. If you already have access to the IEEE collection it is worth a read, but I only read the draft version and am not sure the final version has exactly the information you are looking for.

 

[MIGMIG]

Mr. jghrist
You're right. I mean Catenary curve. you have replied that
there is no way to calculate those spans which are like "S". you don't know any solution for it ?
So how can I figure out that how much force is on the equipments' termination.?
Thank alot.

 

[jdagenhart]

There "shouldn't" be any significant horizontal tension, if what you are describing is correct. If so, then each support point shares half the vertical force of the weight of the span. To be conservative, however, I'd probably allow for some minimal horizontal tension based on some slack span consideration. After all, there has to be "some" horizontal tension.

 

[Marmite]

Depending on where you are you might want to factor in ice accumulation and wind loading, both of which could result in horizontal force.
Chapter 4 of the ABB switchgear manual may be of assistance.
Regards
Marmite

 

[Marmite]

See attached for guidance on calculating sag on slack spans.

http://books.google.co.uk/books?id=...resnum=2&ved=0CBMQ6AEwAQ#v=onepage&q=&f=false

Page 107/108.
Regards
Marmite

 

[jdagenhart]

Has anybody had any experience with using a device from LaserTech to measure sag directly?

http://www.lasertech.com

It is represented to do so much like a total station would do.

 

[MIGMIG]

Dear Mr. Marmite
I Saw your link and check that book which you had suggested
me. But it was only some chater of that book . Do you have electronic file of that book ?
I thank you very much.

 

[PHovnanian]

When short spans stop approximating caternary curves (your S shaped jumpers), modeling their loading on supports (and equipment bushings) becomes more of a rigid structure problem. The stiffness of the short spans, bus structures and jumpers needs to be taken into account. Also, the movement of the structures due to wind, snow loading and earthquakes will affect the mechanical loads transferred to support structures.

 

[jghrist]

Once you figure out the weight on the support insulator strings, you can determine the horizonal force if you know the angle of the insulator strings from horizontal.

This won't help to predict the horizontal force at cold temperatures or with ice loading.