Sag Template

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Sag Template 

1) Sag template is used for allocating the position and height of the supports correctly on the profile. 

2) The sag template is usually made up of transparent celluloid, perplex, or somtimes cardboard.

3) Sag template defines the limit of minimum clearance angle between the sag and the ground for safety purpose.

Curves marked on the sag template are :
1) Hot template Curve or Hot Curve
2) Ground Clearance Curve
3) Support Foot or Tower Curve
4) Cold curve or Uplift Curve

                               fig : 1

(Note : Above image is enlarged in fig 2 )
 
                                 fig : 2



Hot Curve : The hot curve is obtained by plotting the sag at maximum temperature against span length. It shows where the supports must be located to maintain the prescribed ground clearance.

Ground Clearance Curve : The clearance curve is below the hot curve. It is drawn parallel to the hot curve and at a vertical distance equal to the ground clearnce as prescribed by the regulation for the given line.  

Support Foot Curve : This curve is drawn for locating the position of the supports for tower lines. It shows the height from the base of the standard support to the point of attachment of the lower conductor. For wood or concrete line, pole line , this curve is not required to be drawn since they can be put in any convenient position. 

Cold Curve : Cold curve is obtained by plotting the sag at a minimum temperature without wind price against span length. This curve is drawn to determine wheather uplift of conductor occurs on any support. The uplift of conductor may occur at low temperature when one support is much lower than either of the adjoining ones.  

Stringing chart 

1) Stringing Chart is a plot of transmission line tension and sag as a function of temperature.

2) It is plotted taking into account the limiting values of sag or tension with a factor of safety to be occurring at the worst condition . ( i.e. with ice deposit and windy condition )

3) The amount of sag or tension to be kept at erection conditions can be determined with this chart. 



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