To answer some of Rodalco's original questions:
I think the most common voltage for new installs is 19 kV. I know it is in some African countries (like Namibia) and I've seen transformers for this voltage from Thai manufacturer as well. You can use the same insulators as for 33 kV 3-ph systems.
Distribution systems up to 33 kV have been built, in South Africa e.g.
If you run the calculations, you will see that raising the voltage overcomes some of the inherent limitations of a SWER system. You get other problems instead, of course.
Suggestions for 80 kV, 6 MW SWER transmission systems have been made for Alaska. Not built, AFAIK.
