wye -> delta transformer

[mivey]

What would happen for the 3 single phase loads if the voltage was exactly the same on all three phases but, the loads were all different? Would you expect to have zero-seq current or not?

But of course. Three exact voltages (evenly distributed phase angles) across three different impedances (assume some consistency in power factor) will produce three currents that won't sum to zero.

 

[GoldDigger]

But there will not be parasitic circulating currents.
If you have unbalanced currents from line to line on a delta it does *not* cause current in the neutral of a wye primary.
If you put a single line to line load on one side of a delta secondary it will be fed by both the immediately adjacent coil and the other two coils in series. The result is current in all three hot wires of the wye primary and *no* current in the wye neutral.
If you take a single phase transformer rather than three pots or a common core three phase pot, then you must, of course, have current in two wires on the primary side.

 

[electrofelon]

Thanks for the explanations, that makes sense. I appreciate it. Next fun think to do is to hook this baby back up as it was, put a watthour meter on it and see how much extra they have spent on power for the 15 years they have owned the building :jawdrop: I hope the guy who hooked it up was cheap

 

[Bugman1400]

But there will not be parasitic circulating currents.
If you have unbalanced currents from line to line on a delta it does *not* cause current in the neutral of a wye primary.
If you put a single line to line load on one side of a delta secondary it will be fed by both the immediately adjacent coil and the other two coils in series. The result is current in all three hot wires of the wye primary and *no* current in the wye neutral.
If you take a single phase transformer rather than three pots or a common core three phase pot, then you must, of course, have current in two wires on the primary side.

I believe your term of "parasitic circulating current" is just another way of saying negative-sequence current.....right? It is one of the three sequence currents like zero-sequence current. And, for the unbalanced, single-phased loads (Line-to-neutral), why wouldn't you have negative-seq currents? I don't dispute with having no zero-seq current for unbalanced, phase-to-phase loads.