I give a short introduction to the differences between autotransformers, variable autotransformers and variable transformers. I show my collection of 7 variacs/variotransformers in the range from 1x260V @ 2A to 3x400V @ 25A along with a 3x400V 10kVA isolation transformer.
3x400V @ 13A Variac demonstration with data monitor: https://www.youtube.com/watch?v=PqeLLLZTBb8