Vindi...
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.
Last edited by Tesla; 08/31/11 05:48 PM.
