BALANCED WYE- WYE CONNECTION

Balanced Wye - Wye Connection

• The wye-wye arrangement requires a neutral connection between the source and the primary of the transformers not only to assure balanced line-to-neutral voltage, but also to provide a path for the third-harmonic component in the exciting current of the transformers. Without the primary neutral connection, serious unbalances in the line-neutral voltage may result from (a) unequal exciting admittances among the three transformers and (b) unbalanced line-to-neutral loads in the secondary. Furthermore, if the third harmonics are suppressed in the exciting current, large third harmonic components may appear in the line-to-neutral voltages. The wye-wye arrangement is, therefore, a four-wire system if balanced voltages are to be assured. The delta-delta arrangement is, on the other hand, a 3-wire system.

In the three phase circuit arrangements displayed, each leg is shown with an impedance. If the impedances are identical on each phase, then the load is said to be balanced. A three-phase source is balanced when each leg produces equal magnitude voltage, with phase difference between any two phases.