ACSR 795 MCM, Drake, 26/7 Conductor rating

[adi 3291]

As per our study this 138kV, ACSR 795 MCM transmission line at the ambient conditions of(104 °F, 2ft/s, 45° wind angle) result in a conductor temperature of 172.2°F at a Max current of 689A and conductor is rated for a Max temperature of 212° F.

But as per ACSR conductor behavior, as temperature rises from 172.2°F, aluminum expands more rapidly than steel. Eventually, the aluminum tension will reduce to zero and then go into compression. Beyond this point, the steel carries the total conductor tension. These compressive stresses generally occur when conductors are operated above 176 °F to 200 °F. Greater sags than predicted at these elevated temperatures may be attributed to aluminum being in compression.

So when we want to rate this transmission line, what should be the maximum ampacity rating to consider? Considering the max ampacity of 689A will gives us a rating of 1.732 x 138kV x 689A = 165 MVA only.

I found the Ampacity ratings of ACSR conductor as below. What should be the temperature tolerance limit to consider, without significantly affecting the conductor life span?

 

[bacon4life]

Check out

https://www.powline.com/usrgroup/ma...lic_Conductor_Models_-_Why_and_What_Value.pdf

for more info assumptions for aluminum compression.

My impression is that new lines in my region are all being built with clearances for operation for at least 212 degree F. Designing the clearances for lower temperatures really limits the ratings during emergency conditions. If this line is already constructed, hopefully you can find the original design documentation.

As to whether a line should regularly be operated above 167 degrees F, that is a somewhat different question. Many components have decreased life above 167 degrees F, and some hardware manufacturers note that their hardware is not rated for operation at 212 degrees F. Some utilities have have specific limits for operation above 167 F such as a limited number of hours per year. Other utilities required thermal imaging of a line after any operation at elevation temperatures.