ACSR 795 MCM, Drake, 26/7 Conductor rating

[adityalagudu3291]

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 above. What should be the temperature tolerance limit to consider, without significantly affecting the conductor life span?

 

[jdsmith]

It depends what country you’re in and what regulations you need to comply with. In the US there are different requirements for how line ampacity is calculated depending on whether the line will be regulated as part of the bulk electric system or whether it is not BES, such as a circuit on the premises of an industrial plant. For industrial plants where I am interested in calculating a single line rating, not seasonal or any type of dynamic ratings, I’ve gone through all of the detailed calcs with similar wind speeds, temperature, etc that you listed and concluded that the ampacity values in the Southwire overhead conductor manual or the Westinghouse T&D book are pretty much spot on for a single, conservative rating for industrial use.

If your line will be part of a utility system and subject to additional regulations, then follow whatever the regulator requires.


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[Julius Right]

From Aluminum Electrical Conductor Handbook [1989] :
It seems the creep it is important in temperature limitation.
Creep depends on conductor temperature and 60oC temperature rise it is considered the limit. Usually it is indicated not to go up to 75oC.