Delta/Wye transforms cause a 30 degree phase shift... with the Wye lagging the Delta... It's in Ugly's -- the fine print.
BTW, Delta and Wye are TENSOR diagrams. So you can visually see the math by placing the star inside the delta and note that the star tensors bisect the delta's wedge -- each wedge is 60 degrees -- and cutting it in half gives you the 30 degrees lagging shift.
But enough Vector Algebra...
Wye/Wye transformers use more wire -- to no good purpose.
The windings ratio in a 480 to 208Y120 is 4:1...
This reality is beyond many electricians, I've been on the end of many flaming posts because of such belief. Some j-man think that the ratio is 480/208 -- which is entirely false. For those disputing this... open up a transformer and trace the connections. ( Turn it off, first. )
The delta connection is H1-H2 : 480 volts
The wye connection is L1-N : 120 volts
Wye-Wye transforms also permit noise from either side to crossfeed.
There are occasions where you'll find wye-wye: massive DC power supplies used to drive electro-chemistry: aluminum reduction, chlor-alkalai plants and such. They use a mix of delta-wye and wye-wye to phase shift -- creating 12 phase power from 3 phase. At that point the AC is rectified with a massive low pass filter -- thence to the reduction line.
This came up for me when using large step-up step-dn transformers on large scale PV projects, several 'other' engineers wanted to use a y/d-d/y configuration and it took forever to get across to them that there was no (easy/cheap) way to open a fault that way so they proposed a y/d-y/y configuration, which would work (noise was not an issue), but the additional cost and lead time was not worth it.
We standardized on a y/d-y/d configuration, but still wound up with one installation with a y/d-d/y configuration where we corner grounded the delta on the utility side of the run.
I still remember the jw and foreman calling me asking repeatedly, "this is going to work when I throw the switch right?" and the total surprise in their voice when they called back to say "damned if it doesn't work!".
Interestingly enough I discovered that a LOT of utilities use Wye/Wye transformers within their own distribution networks.
Greg's Image above looks like a MGCN setup (Multi-Grounded Common Neutral).
The Primary -appears- to be connected as a Wye, but I am not 100% sure.
The Secondary must be Wye connected, as the Left-Side Bushing of the Two visible Pots has only a single lead with no interties; and the Right-Side Bushings have Bare Leads, which appear to be heading to the Star Point + MGCN termination.
Greg, do you have a Non-marked Up version of this Pole's Setup?
Scott " 35 " Thompson Just Say NO To Green Eggs And Ham!