In the deregulated market of electric transmission power systems today and as the energy demand continues to increase, electric utilities are faced with the challenge of moving more power via existing lines while at the same time obtaining permission for the erection of new lines and upgrading of existing lines becomes increasingly more difficult. 

As a result, power utilities and system operators are currently looking for opportunities to increase the capacity of the existing OHTLs without increasing the risk of equipment or system failure due to higher loading and an accelerated aging of the transmission infrastructure. One approach to manage the reliable operation of these systems is to utilize modern monitoring techniques as a method to prevent unexpected system outages. 

On OHTLs the sag of the individual line is an operational and security concern, which directly relates to the conductor operating temperature. The conductor operating temperature is influenced by various conditions eg. line losses, ambient temperature, wind speed and direction, solar radiation and 
conductor material properties. 

During periods of high ambient temperatures, low wind speed and high electrical system load conditions, monitoring and analyzing regional areas of the transmission network can be essential  to evaluate the actual conductor operating temperature for the purpose of optimizing the line capacity and to prohibit potential sag problems. 

For measuring the conductor temperature of an overhead transmission line a sensor, which will have approximately the same thermal behaviour as the conductor, can be mounted on the conductor. Due to the high electrical and magnetic stresses in the area surrounding the overhead transmission line, a purely passive SAW sensor is used. The temperature of the conductor at the point of installation can be measured and 
the data transmitted wirelessly by means of a radio frequency backscatter (radar principle) to a data collection 

Along the overhead transmission line, installed passive sensors observe the temperature of critical line locations allowing continuous monitoring of the line behaviour. The measuring principles of the SAW sensor, the involved radar system components as well as current applications are presented. 

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