Delta Winding with grounding transformer on utility sub-transmission & distribution

[rockman7892]

I've come across a few small municipal distribution systems recently that had either their sub-transmission or distribution systems served from and interconnection substation to local transmission system owned by others (larger IOU) and noticed that the low voltage side of these transformers for municipal sub-trans or distribution (IE 26kV or 12.47kV) was a delta winding with a grounding transformer.

I found this a bit odd as most of these transmission to distribution level transformers I've come across in the past have always had a wye winding. Would there be any particular reason for having a delta winding on the low side of a sub-transmision or distribution transformer? Only thing I could think of would be the presence of generation on sub-transmission or distribution?

Appreciate any insight from others who may be familiar with approach.

 

[waross]

That would stabilize the incoming voltages.
That MAY allow a ride through of a primary loss of phase if the incoming was a wye configuration.
The downside of that is that it would back-feed full voltage into a lost primary phase.