aka Corner-Grounded Delta. I just looked that up because I'm no expert. One transformer with three secondary taps. One tap (B) grounded. So A & C are 240V to ground.
Advantages: - cheaper 2-pole gear can be used all down the line - there are only three conductors just like split phase 240V - B phase does not have to be (and CANNOT be) switched or fused.
But this is not what the OP has.
Also I ran across something on Wikipedia that mentioned that the old power station at Niagara Falls was two-phase. Maybe that was where I'd heard that before. -- USNG: 16TDN2870 Find your USNG coordinates: USNGWeb
whizkid3 Premium,MVM join:2002-02-21 Queens, NY kudos:9
4-wire, 3-phase 208/120 from a wye secondary on a transformer. Tie into any two phase conductors and the neutral, and you have single-phase 120/208. (Regardless of what they were doing in Niagara Falls ages ago.)