# How to estimate active-power transmission capacity based on voltage levels and line lengths

I know voltage levels and line lengths of high-voltage transmission lines and I am looking for a rough estimation of the maximum active-power transmission capacity during normal operation. By normal operation I mean power levels that can be sustained over long durations. I understand that many factors are impacting this and that a 1-to-1 map from voltage to active power level is hard to give. But I am looking for rough estimations only, and I am happy with any upper-bound, lower-bound, or range estimations.

An example would be: out of my window, I can see a transmission line and all I know about it is that it's a single-circuit 220 kV line. In which range will the active power capacity of this line be?

• Well, thermal aspects, given that the line is already rated for the voltage you're planning to operate on, are pretty much the only limiting factor I can think of. How "large" is "this estimation is rather large"? – Marcus Müller Apr 3 '20 at 10:49
• Usually transmission line voltage drop is the design criterion rather heating. – Transistor Apr 3 '20 at 10:50
• 1 GW springs to mind as a rough value. – Andy aka Apr 3 '20 at 10:56
• @MarcusMüller if the thermal limit is the only limit in your opinion that's an answer I would say. Is it possible to estimate the thermal limit from voltage level? – Tim Tröndle Apr 3 '20 at 11:01
• No, thermal limit will be related to $I^2R$ where R is the cable resistance. Line voltage is not a factor. – Transistor Apr 3 '20 at 11:03