# What is Sag & Tension in transmission lines & Formula Calculation

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## Sag & Tension  in transmission line

### Factors Affecting Sag

#### (ii) Location of conductor

Sag also depends on the location of conductors.If the conductors are present in the area where ice formation takes place, then due to the accumulation of ice on the conductor its overall weight increases.This increases the weight of the conductors which in turn increases the value of sag.

(iii) Length of span

Sag is proportional to the square of the length of the span.Hence, longer the span greater will be the sag provided the tension and weight of the conductor are constant.

(Vi) Tension

### Calculation of Sag in Overhead transmission lines:

(i) When supports are at equal levels

#### l = Length of span w = Weight per unit length of conductor T = Tension in the conductor.

Now consider any point on the conductor. Let’s say point ‘P’.By considering lowest point O as the origin, let the coordinates of point P be x and y. Assuming that the curvature is so small that curved length is equal to its horizontal projection (i.e., OP = x), the two forces acting on the portion OP of the conductor are :
(i) The weight wx of conductor acting at a distance x/2 from O.
(ii) The tension T acting at O.

#### y=Tx²/2T

The maximum dip (sag) is represented by the value of y at either of the supports A and B. At support A, x = l/2 and y = S

### (ii) When supports are at unequal levels

The difference in level between points of supports and the lowest point on the conductor is called “sag”.When transmission lines run on steep inclines as in the case of hilly areas, we generally come across conductors suspended between supports at unequal levels.The shape of the conductor between the supports may be assumed to be a part of the parabola. In this case, the lowest point of the conductor will not lie in the middle of the span.

#### and Sag S2 = wx2²/2T

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