4. If a wye (primary) – delta (secondary) transformer connection
is used, a grounding transformer has, in effect, been installed
on the feeder. Even when the DG is not operating, a ground
current will follow for faults on the supply feeder as well as for
ground faults on any of the feeders connected to the same bus
as the DG feeder. In addition, an unbalanced load―which on a
four-wire system shows up as a zero sequence current―will
be divided between the substation ground source and the DG
transformer. This can result in tripping at the DG location by
ground overcurrent relaying in the DG transformer neutral.