Open Wye

[benray]

Has anyone ever connected a transformer bank in open wye/open wye configuration?

 

[Lewish]

I thought that was called V-phase/V-phase. At least it was 40 years ago in the oil fields in the South.

 

[benray]

Yes, this is known as a V/V, which can be an open delta or open wye.
Open delta is usually 120/208 with a stinger leg. The secondary neutral is grounded and directly connected to the supply MGN, for through fault containment.

Open wye is usually 480 secondary phase volts. The center point(neutral) is earthed. The two ungrounded phases will be 277 volts to ground, the center connection will be zero to ground. This system must have interconnection of the MGN and secondary neutral at the transformers, for through fault containment.

The open delta and open wye systems are not in use much now days. They were economical to install, but limited for specific applications.

 

[busbar]

Sort of…OY-to-OD. A number of years ago there was a small bakery going into some rental retail space that had 3-wire (2ø+N…120/208) network service furnished by the building owner, and tenant had a 230V 3ø mixer. Using two drytypes strapped 240:120, the shop’s open-wye electric service was able to power the mixer through open-delta 240V transformer windings.

The street side of the building was utility-served 208Y/120V 3ø 4w, but the shop was fed from a common metering location through a ~100-ft 150A 3-wire feeder, whose cost to change was beyond the tenant’s budget.

Voltage balance at the mixer-motor’s terminals was not perfect, but for the load and duty at hand, worked well.