Higher voltages for generators

Generators ever grow in size, transmission lines ever grow in length and voltage, but the generator voltage remains forever. So it would seem when looking back upon the enormous development of the electrical industry in the last few years. Nothing stood still; everything seems to have progressed except the generator voltage. Is there a law of nature or a constitutional amendment against the use of a generator voltage over 13,800? To be sure there are difficulties. But were there no difficulties in designing huge transformers and turbines or 220-kv. oil breakers? The study and development of insulating materials, iron and other features affecting generator design has not stood still; a great deal more is known about these features than was known twenty years ago, and more can be done withthem.