As a preface, this is purely hypothetical. I know better than to use a transformer without knowing anything about it. I'm just trying to get an idea of whether this is possible, not whether it's a good idea.
Let's say I have a three-phase transformer that I know nothing about. I have three primary leads and three secondary leads, and that's it. No markings or anything, no datasheet, just a box with wires sticking out of it.
Is there any way to determine with external measurements how the windings are wired? I know that I can look at phase shift between primary and secondary to determine whether it's Y-Δ, but if there is no phase shift, is it possible to distinguish Y-Y from Δ-Δ? If there is phase shift, is it possible to determine which winding is Y and which is Δ?
Ideally I'd like answers that only involve measurements and physical properties. I'm aware there are conventions like using Δ on the high side of a Y-Δ transformer, but assume this transformer was wired by someone completely ignorant of any and all conventions and common sense. That means that either side could be Y or Δ without regard to relative voltages, and the neutral wire on a Y connection may not be present. You can assume the transformer is balanced, however, with three identical primary windings and three identical secondary windings.
Best Answer
There is no way to determine, by external measurements, whether a 3 phase transformer's primary and secondary windings are connected in star or delta configuration.
That's because there is no parameter intrinsic to either star or delta connection.