SAG in electrical power transmission.

What is  Sag.?

In electrical power transmission and mechanical design of overhead transmission line.

SAG.

A perfectly flexible wire of uniform cross-section, when string between the two supports at the same level, will form a catenary. However, if the sag is very small compared to the span, its shape approximation a parabola.

 The difference in level between the point of support and the lowest point on the conductor is known as sag 

The factors affecting the sag in an overhead line are given below.

1. Weight of the Conductor,

 This affect the sag directly. Heavier the conductor, greater will be the sag. In locations where ice formation takes place on the conductor, this will also cause increase in the sag.

2. Length Of the Span.

This also affect the sag. Sag is directly proportional to the square of the span length Hence other conditions, such as type of conductor, working tension, temperature etc. remaining the same a section with longer span will have much greater sag.

3. Working Tensile Strength.

The sag is inversely proportional to the working tensile strength of conductor if other conditions such as temperature, length of span remain the same. Working tensile strength of the conductor is determined by multiplying the ultimate stress and area of cross section and dividing by a factor of safety.

4. Temperature.

All metallic bodies expand with the rise in temperature and, therefore. The length of the conductor increases with the rise in temperature, and so does the sag.

Reference from .

Transmission and distribution of electrical power by-J.B.Gupta.

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The Part of Electrical Distribution system

The Electrical Distribution system  further be divided into following.

Feeders, Distributors and Service Mains.

1.Feeders.

Feeders are the conductors which connect the stations (in some cases generating stations) to the areas to be fed by those stations.

Generally from feeders no tapping is taken to the consumers therefore current loading of a feeder remains the same along its length. 

It is designed mainly from the point of view of its current carrying capacity 

2.Distributors. 

Distributors are the conductors from which numerous tapping’s for the supply to the consumers are taken. 

The current loading of a distributor varies along its length. Distributors are designed from the point of view of the voltage drop in them.

3.Service Mains.

Service mains are the conductors which connect the consumer's terminals to the distributor.

Distributor is subject to the legal requirement that the voltage at the consumers terminals should be maintained within +/- 6% of the declared (or rated) voltage.

However, there is no such legal restriction on a transmission line and the voltage can vary as much as 10% or even 15% due to variations in loads.

Reference from.

Transmission and distribution of electrical power by- J.B.Gupta

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