Overhead line sag and tension relationship

Sag & Tension in overhead Line? - Definition & Factors Affecting it - Circuit Globe

overhead line sag and tension relationship

internal relations between the measured parameters are examined. The measured parameters are overhead line sag, line temperature, ambient temperature, .. When the conductor elongates due to temperature change the tension within the. This explains what is Sag and Tension in electrical transmission lines(overhead lines).How to calculate sag and effect of wind & ice loading on overhead lines. Analysis of the sag and tension is important in the transmission line for the continuity and quality of electrical services. If the tension of the conductor is increased.

As discussed earlier in this post, enough Sag shall be provided in overhead transmission line to keep the tension within the safe limit. 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.

Now, we will calculate the Sag in an overhead transmission line for two cases. 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.

Sags, Tensions and Guying of Distribution Poles

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. Assuming O as origin, the coordinate of point P will be x,y.

overhead line sag and tension relationship

As this section OP is in equilibrium, hence net torque w. When the conductor supports are at unequal level.

Calculation of Sag & Tension in Transmission Line - for Level & Unlevel Span -Circuit Globe

In hilly area, the supports for overhead transmission line conductor do not remain at the same level. Figure below shows a conductor supported between two points A and B which are at different level. The lowest point on the conductor is O.

overhead line sag and tension relationship

If the amount of sag is very low, the conductor is exposed to a higher mechanical tension which may break the conductor.

Whereas, if the amount of sag is very high, the conductor may swing at higher amplitudes due to the wind and may contact with alongside conductors.

What is Sag & Tension in transmission lines & Formula Calculation

Lower sag means tight conductor and higher tension. Higher sag means loose conductor and lower tension. Therefore, a suitable value of sag is calculated so that the conductor remains in safe tension limit keeping the sag minimum.

The tension at any point on the conductor acts tangentially.

overhead line sag and tension relationship

Therefore, the tension at the lowermost point on the conductor is horizontal. The horizontal component of tension at any point on the conductor is constant.

overhead line sag and tension relationship

The tension at the support points is nearly equal to the horizontal component of tension at any point on the conductor. Calculation of sag The tension on a suspended conductor is governed by the conductor weight, effects of wind, ice loading and temperature variations. The value of sag is calculated for two different scenarios - i supports are at equal levels and ii supports are at unequal levels.

Sag in Overhead Conductor

When supports are at equal levels Consider a conductor suspended at supports of equal heights as shown in the figure below. A and B are the support points and O is the lowest point on the conductor.

overhead line sag and tension relationship

Considering the lowest point O as the origin, let the coordinates of point P be x and y.