How much power can transit through a power line linking generation and load?
Your calculations look correct.

Several factors can affect the maximum load:


Maximum allowable voltage drop.
Transformer rating at each end.
Switchgear and protection device ratings.
Heating effect in the cable.


All of these have to be assessed and the first limit you hit determines the power limit.

I notice that you are specifying a 0.8 PF operating condition. Bringing this closer to 1.0 PF will result in lower currents with resultant decrease in voltage drop. This may require addition of power-factor correction equipment by your users. The traditional method of encouraging good power-factor is to charge a low power factor financial penalty for anything below 0.95 PF.