In delta/wye power, there is an inherent phase difference between whether you're measuring line-to-ground or line-to-line. Basically, the peak measured A-to-neutral is going to peak about 30 degrees after A-B peaks, and about 150 degrees after C-A peaks. Usually, this is described as the delta leading 30 degrees behind wye (or that the wye lags the delta by 30 degrees)
It helps to draw a phasor diagram to picture this- if you draw a wye system and then connect the peaks to create the delta vectors, it should make sense pretty quickly.
The problem is when you wire up a transformer delta-wye, as the transformer now ties in the wye to the phase angle of the delta, which bumps the whole thing by 30 degrees.
This only occurs in 3-phase. There's no phase shift in 1-phase.
Edit: had something backwards
[This message has been edited by SteveFehr (edited 10-26-2006).]
