Category: Formula for sagging wire

Formula for sagging wire

Sag in overhead Transmission line conductor refers to the difference in level between the point of support and the lowest point on the conductor. Sag in Transmission line is very important. While erecting an overhead Transmission Line, it should be taken care that conductors are under safe tension.

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If the conductors are too much stretched between two points of different Towers to save conductor material, then it may happen so that the tension is conductor reaches unsafe value which will result conductor to break. Therefore, in order to have safe tension in the conductor, they are not fully stretched rather a sufficient dip or Sag is provided. The dip or Sag in Transmission line is so provided to maintain tension in the conductor within the safe value in case of variation in tension in the conductor because of seasonal variation.

Some very basic but important aspects regarding Sag are as follows:. Now we consider a case where the point of support of conductor are at same level but the Sag is very less when compared with the span of conductor.

Sample Calculation of Sag and Tension in Transmission Line – Uneven Elevation

Here span means the horizontal distance between the points of support. In such case, the Sag-span curve is parabolic in nature. Thus the tension at the lowest point of the conductor acts horizontally while at any other point we need to resolve the tangential tension into vertical and horizontal component for analysis purpose.

The horizontal component of tension remains constant throughout the span of conductor. As discussed earlier in this post, enough Sag shall be provided in overhead transmission line to keep the tension within the safe limit.

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The tension is generally decided by many factors like wind speed, ice loading, temperature variations etc. Normally the tension in conductor is kept one half of the ultimate tensile strength of the conductor and therefore safety factor for the conductor is 2.

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Now, we will calculate the Sag in an overhead transmission line for two cases. Case1: When the conductor supports are at equal level. Let us consider an overhead line supported at two different towers which are at same level from ground. The point of support are A and B as shown in figure below. O in the figure shows the lowest point on the conductor.

This lowest point O lies in between the two towers i.The midspan cable and horizontal support forces with uniformly distributed load can be calculated as. The horizontal supports and midspan cable forces can be calculated as. Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your Sketchup model with the Engineering ToolBox - SketchUp Extension - enabled for use with the amazing, fun and free SketchUp Make and SketchUp Pro.

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In one of my physics textbooks there is a chapter on the elasticity of materials which contains pretty basic outline about Young's modulus, stress-strain, elastic potential energy and related stuff. There is only one thing stated in the book which I didn't understand, which is this:. The book says that it can be derived easily with basic concepts of elasticity and some calculus.

What I tried was:. Despite many efforts, I could not arrive at the result.

formula for sagging wire

Can anyone please help me in proving this result? At every point along the beam, the curvature has to be such that the externally applied bending moment exactly counters the internal stress. This tells you that the curvature is not constant - it is a function of distance to the side largest in the middle, zero at the wall. This means that your assumption of "circular section" is wrong. See for example figure 3. Now we need an expression for the bending moment as a function of position.

Knowing that the radius of curvature is for small deflections inversely proportional to the second derivative of the shape, we can write. This expression agrees with equation 7 at this reference. Sign up to join this community. The best answers are voted up and rise to the top.

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Home Questions Tags Users Unanswered. Where does this formula for sagging of a beam come from? Ask Question. Asked 5 years, 1 month ago. Active 5 years, 1 month ago. Viewed 7k times.In this example we will calculate the sag and tension if the conductor supports are at different elevation. Creep is not considered as a factor in final sag in this calculation. Also, loading of the conductors are based on the National Electrical Safety Code A transmission line conductor was strung between two towers Structure 1 and 2meters apart and different elevation as shown in the figure above.

Line 3 is 12 meters above the ground and the distance between phases is 3 meters. Note: The elevation profile between the towers were derived from google earth. This is good for graphical presentation and initial planning.

Calculate the sag and tension at:. The equations derived for the even support elevation can be used to analyze the uneven conductor support heights. Below are the derived equations: see the figure. The horizontal component of tension are the same at all point in the conductor. However, the vertical component of tension at the upper support is greater, hence the total tension at that point is also greater.

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S — horizontal distance between conductor supports. S L — straight line distance between conductor supports. L — total initial conductor length. Solving the conductor sag D see figure above :. Solving the horizontal distance:. Total conductor length:. Initial Sag:. We can see the lowest point of the conductor is closer to the lower conductor support. Also, the difference between the horizontal span S and total conductor length is just 3. Calculate wind load. Total unit weight.

Final Conductor tension, H 2.Hot Threads. Featured Threads. Log in Register. Search titles only. Search Advanced search…. Log in. Forums Engineering General Engineering. JavaScript is disabled. For a better experience, please enable JavaScript in your browser before proceeding. Wire sag formula. Thread starter williamlynn Start date Mar 9, I am looking for a formula to calculate the deflection sag in steel wire that is supported between two points with a known tension.

I want to be able to calculate the deflection sag at any point along the wire. Related General Engineering News on Phys. PhanthomJay Science Advisor. Homework Helper. Gold Member. Thanks for quick response; I really need to be able to find deflection along any point in the wire. I'm lloking at. The wire sag is used for turbine machinery alignment; the internal parts of the turbine must be accurately aligned to a centerline.

The wire is the centerline reference but the wire sag must be accounted for to get accurate centerline. Alignment of the turbine components has to be within thousants of an inch. FredGarvin Science Advisor. I can't say that I have ever heard of using wire as a centerline reference.

That doesn't mean people don't use it though. It seems kind of "hokey. That's what we use a lot. That way you can calibrate the pointer position and not have to worry about sag. To do accurate surveys before GPS you used metal wires to measure distance. You support the wire along a string of tripods and apply a known tension with a spring balance, there are tables in old surveying books to calculate the sag - it's just a catenary.

You also have to do this just before dawn when the temperature is stable and the wire has time to acclimatise.

You must log in or register to reply here. Related Threads on Wire sag formula Calculate the moment and the sag. Last Post Nov 11, Replies 1 Views Calculation of sag and tension in transmission line depend on the span of the conductor. Span having equal level supports is called level span, whereas when the level of the supports is not at an equal level is known as unequal level span. The calculation of conductor at an equal level shown below.

The lowest point of the conductor is O. Let the shape of the conductor be a parabola. The weight w. Above equation shows that the sag in a freely suspended conductor is directly proportional to the weight per unit length of the conductor, and the square of the span length and inversely proportional to the horizontal tension H. In hilly areas or sloping grounds, the supports are not usual at the same level. For the calculation of sag and tension at unequal supports level consider a conductor AOB.

The portion of OA and OB may be treated as catenaries of half span x and l-x respectively shown in the figure below. Let.

formula for sagging wire

The tension A and B are given by. The maximum tension will occur at B since l-x is greater than x as seen in the figure above. Vertical reaction at the higher support — w. The value of x obtained above may be substituted in equation 5 to calculate sag at OA. Equation 8 shows that the lowest point lies outside the span AB. Hence, the conductor in the span under consideration exert an upward force, and the conductor tends to swing clear of the lower support.

Your email address will not be published. Save my name, email, and website in this browser for the next time I comment. Circuit Globe All about Electrical and Electronics. Electronic Instrumentation. What is the exact formula to calculate sag…….

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Anybody ever use an iPhone to measure sag using the pulse return method? Leave a Reply Cancel reply Your email address will not be published.Log In. Thank you for helping keep Eng-Tips Forums free from inappropriate posts. The Eng-Tips staff will check this out and take appropriate action. Click Here to join Eng-Tips and talk with other members!

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formula for sagging wire

By joining you are opting in to receive e-mail. Promoting, selling, recruiting, coursework and thesis posting is forbidden. Students Click Here. Related Projects. I am designing a double angle fence post member that has a tension cable attached to its top. See the attached document for a graphical representation. The tension cable spans the width of a pedestrian pathway and is attached to double angle fence posts on either side of the pathway. In order to arrive at the moments at the base of the post, I need to determine the amount of tension in the cable at the post's top.

Which variable is known? I can imagine 2 scenarios: the cable being installed to a limited maximum sag in this case d is known and T can be derived or the cable being pre-tensioned to a minimum tension value in this case T is known and d is derived.

formula for sagging wire

The cable will sag and the posts will bend inward creating additional sag in the cable. See second attached image.


1 comment

  1. Zulurisar on 19.12.2020 at 13:39
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  3. Ich bin endlich, ich tue Abbitte, aber es kommt mir ganz nicht heran. Wer noch, was vorsagen kann?