[EDIT] Can someone who understands what I wrote explain this?
[EDIT 2] Sorry I didn't say I'm in the USA, the power is 110/220vac 60Hz. The input to the main power transformer is 3-phase, underground, the output is 220 with (normally) a center tap for neutral/ground. So lights and plugs are on one side or the other for 110, and heating and cooking range are 220. In this normal configuration it is impossible for loss of power on the input to the transformer to cause only one side of the 110 to be lost. Yet that is what happened to all the units in both buildings. [END EDIT]
I live in one condo unit of a two building 72 unit complex. The entire complex, both buildings run on a single 3-phase power transformer. There is some new construction down the road and their digging equipment hit some wiring and caused a strange power outage that affected many homes around the area as well as our condo units. What is strange is that all the units lost power on only one side of the 220V panel giving 110V on one side and 0V on the other side. I measured the voltages in my own panel. How is a commercial 3-phase transformer wired so that this is possible.
I am an electrical engineer and am familiar with all the normal delta and Y power transformer connections. But I have not found anything in my searching that can explain this outage. The same thing happened about a year ago, same cause. And this one again today.