Sag and Tension Analysis

Conductor sag and tension analysis is an important consideration in overhead transmission and distribution line design. The quality and quantity of electrical service supplied over a line depend largely on whether the conductors have been properly installed. Thus, it is necessary to determine in advance the amount of sag and tension to be given to the conductors at a given temperature. Tension in the conductors contributes to the mechanical load on the supporting structures. The factors affecting the sag of a conductor stung between supports are:
· Conductor load per unit length
· Span, i.e., the distance between the supports
· Temperature
· Conductor tension

The conductor load is calculated based on weight of the conductor itself, weight of the ice or snow clinging to the conductor and the wind pressure on the conductor.
The conductor tension is classified as follows:

1. Initial unloaded tension – State of conductor when it is initially stung (no ice or no wind)
2. Final unloaded tension – After subjected to ice and wind loads or long term creep.
3. Loaded tension – State when it is loaded to the assumed ice and wind loading.
4. Extreme wind tension – When it has a wind blowing on it to a value not less than the 50 year mean, (No ice loading)
5. Extreme ice tension – When it is loaded with 25 to 50 mm of radial ice.

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