Delta - Wye Power Transformers

[TooFar]

Could someone please explain why most power transformers in utility substations are Delta - Wye. Is it because of the imbalance on the load side(Wye) of the transformer. Also, is there a 30 degree phase shift across the transformer.

 

[dpc]

Delta-wye transformers are useful for a number of reasons. For transmission and distribution lines that are solidy-grounded, the delta-wye provides an excellent ground reference and source of ground current for clearing faults. Also, the delta-wye configuration isolates zero sequence current on each side of the transformer so that ground current relaying on one side does not see ground fault current for a ground fault on the other side.

Yes, there is a phase shift. For an ANSI transformer, the low side will always lag the high side by 30 degrees, regardless of the relative position of the delta and the wye windings.

 

[RalphChristie]

See the pros and cons of the different transformer winding configurations at:

http://www.beckwithelectric.com/powerlines/powerlines-37.html