Three Phase Three Wire System

What are some other considerations that go into choosing a Three Wire Delta System rather than a Three Wire Wye System other than budget?

Basically, 3-wire 3-phase systems save one conductor, the neutral, in overhead construction.
In a service (600 volts and under) the source transformer winding is a delta or an open-delta. In California, if the voltage is 240V, then one of the corners is grounded. If it is 480V then it is ungrounded.

As a distribution system, the source transformer is typically a grounded wye winding and the neutral just is not extended outside the substation. The positives: one less conductor and shorter poles in overhead construction. In underground construction there is little to no savings as the required shield can be made so that it functions as the neutral. Also, the system can be easily upgraded to a higher voltage without replacing the distribution transformers by changing them from delta to wye connections. The negatives: single-phase transformers must have two primary bushings instead of one, and the lack of good neutral connection out on the line for connecting protective grounds.


Leave your comment (Registered user only)