What Is Sag And Span In Overhead Lines

July 22, 2020February 25, 2022 CS Electrical And Electronics

Hello Guys, welcome back to my blog. In this article, I will discuss what is sag and span in overhead lines, factors, advantages, disadvantages, effect of ice and wind, etc.

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India and many other countries refer to overhead lines because it has many advantages compared to underground cables. The sag and span are seen in overhead lines. Also, read – Why overhead lines?

Sag And Span In Overhead Lines

What Is A Sag?

When thinking about overhead lines, it is important that the conductors are at safe tension. A sag in the Overhead line refers to the difference in level between the point of support and the lowest point on the conductor. If the conductor is stretched more between the poles then there is a chance of breaking the conductor. In order to permit the safe tension, the sag is provided in the overhead lines.

The different overhead lines have a different sag it depends upon voltage, the sag is the difference between the lowest point of conductor and conductor point at the pole side.

Different Types Of Sag

While calculating sag there are two considerations i.e., types of sag.

There are basically two different types of sag:

01. Sag when the supports are at equal levels
02. Sag when the supports are at different levels.

The sag should be maintained always because if sag is too more then tension is less and more wastage of conductor, whereas if sag is too less then tension is more there will be a chance of break of the conductor. The sag is always inversely proportional to the tension. The tension on the conductors depends upon the following factors such as ice loading, temperature variation, wing effects, and weight of the conductor.

Effect of Ice And Wind

When the wind blows by a certain force and ice is formed around the conductor than the weight per unit length of the conductor is changed.

Factors On Which Sag Depends

01. Tension – We all know that sag is inversely proportional to the tension when tension is more sag is less and when tension is less sag is more.
02. Climate- If the temperature is more sag is increased and if the temperature is less sag is also low.
03. Weight of the conductor- The weight of the conductor is directly proportional to the sag, Due to the ice and wind loading the weight of the conductor is increased.
04. Span- The distance between the two structures is called the span. If the span is more then sag is also more.

Advantages Of Sag

01. It reduces tension on the conductor.
02. It will be safe for lives
03. Less chance of conductor break.

Disadvantages Of Sag

01. Ground clearance increases.
02. Cost increase.
03. More conductor is required.

What Is Span In Lines

The horizontal distance between the two structures or pole is called span. If the span is longer then fewer towers are required but the tower should be taller and the cost of the tower will be more. If the voltage is more then the span will also be more. The span for the higher voltage is between 200 meters to 400 meters.

Span For LT and HT Line