Hello All
I have been quietly following this discussion, and have been slightly surprised that no one has pointed out that all of this is covered in Standards.
Power Transformers are covered in the international IEC specification
60076-1, and unfortunately there is also an American standards C57.12.00, and C57.12.90, and they do not totally agree.
If you want to get some idea of the differences put "IEC transformer" into your search engine, and fairly high up the hits you will find a PDF comparing the International & American standards.
John