EUSERC Hates ungrounded systems...
Because of all of the issues triggered by sub-system faults.
Faults like bad motor capacitors, bad windings in either transformers or motors can produce astonishing voltage peaks in ungrounded systems.
Now that Congress has legislated high efficiency solid-state switching devices ( electronic ballasts ) and VFD's are going everywhere grounded systems are the only way to go.
The only ungrounded systems that make any sense are those industrial plants that just can't afford an uncoordinated shut-down. (A paper mill being a prime example.)
I hate ungrounded control circuits. The back-EMF swings of full voltage contactor logic all too often trigger chatter.
------
If you need a reference neutral for an ungrounded delta think in terms of a zig-zag transformer with controlled impedance. In which case, I'd have it engineered.
