Calculation of Sag in Equal and Unequal Levels

Express the calculation of Sag in equal and Unequal levels

In an overhead line, sag should be so adjusted that tension in the conductors is within safe limits. The tension is due to the effect of conductors weight, effects of wind, ice loading and Temperature variations.

1. When Supports are at equal Levels:

Consider a conductor between two equal supports A and B with O as the lowest point of conductor. Consider a point P on the conductor.

Taking the lowest point O as the origin, let the coordinates of point Pat x and y. assume the curved length is small and equal to x. two force acting on the portion OP of the conductor are,

• The weight W.x of conductor acting at a distance X/2 from O.
• The tension T acting at O.

2. When Supports are at Unequal Levels:

In hilly areas, we generally come across conductors suspended between supports at unequal levels. Conductor suspended between two poles A and B which are at different levels.

If w is the weight per unit length of the conductor, then

Having found x1 and x2, the values of S1 & S2 can be easily calculated.