We one time closed up an open delta on a project - in order to increase overall system capacity (as the previous poster indicated). As I understand it, an open delta behaves exactly the same as a normal delta (secondary connection) except at only about 67% of nameplate KVA capacity - which makes sense because one of the three transformers is missing. External wiring is exactly the same.

Also, if I remember correctly, the POCO primary was not a delta, but a wye, which I could not ever seem to explain to the POCO personnel we encountered.

Radar

There are 10 types of people. Those who know binary, and those who don't.