One-to-one three phase transformers have a turn ratio of 1:1 or near 1:1. Variable transformers are three phase devices with a setting for changing the turn ratio as needed. Step-up transformers ...

Single-phase transformers with a 1:1 ratio can be used to isolate circuits. Single-phase transformers abide by Ohm's law, and outside of minor inherent loss due to heat, do not create or remove power.