Conductor sag of a transmission line is an important parameter for evaluating the safety of the transmission line

and it is also one of the key parameters in on-line monitoring and dynamic expansion of capacity of the transmission line. For real-time control of transmission line’s operation

on-line monitoring of conductor sag has attracted great attention in the world

consequently

several mature monitoring methods have been presented. According to the applications

the authors analyze and compare three on-line monitoring methods of conductor sag in terms of their monitoring accuracy. Three methods use conductor temperature sensor

tension sensor

and tilt angle sensor

respectively

to monitor the conductor sag. The results show that if the accuracy of the sensors is high enough

three methods can all meet the requirement of engineering with the errors below 4%

of which the monitoring method with tension sensor gets the smallest error of 1%.