Introduction

• There is a growing need to increase the power handling capacity of existing power transmission assets.

• There is fierce opposition to the construction of new lines and the ability of obtaining right of ways is more and more difficult.

• As a result: increasing the thermal rating of existing overhead transmission lines is seen as a valid alternative to the construction of new lines. 

• One of the prime physical limits on overhead transmission lines is conductor sag.

• Sag is limited to meet the clearance requirements

_of the line,

_between the line and ground, and

_between conductors, under maximum load conditions.

• If the sag is too large, it may cause

_a short circuit between the line and objects below it or

_a short circuit between lines in extremely windy conditions.