Looks like a 3 phase transformer, likely inside the first phase's core is at top, then in the middle the 2nd phase's core, and at the bottom the 3rd phase's core. I see 3 insulated primary feeds, so it may be a delta primary and likely a Y secondary. I once lived in an apartment complex fed by such a transformer, and each apt had 120/208V, 2 of the 3 phases.
