2013年5月21日 · The primary and secondary of a three-phase transformer can be designed as Delta/Delta, Wye/Wye, Delta/Wye and Wye/Delta. Delta/Delta is used in many industrial installations, while Delta/Wye is the most common configuration. Wye/Delta is used in high voltage transmission, and Wye/Wye is seldom used because of potential unbalance.