As voltage increases, at what point does saturation of the core of a typical dry-type distribution and/or buck-boost transformer begin to happen? I would assume not for at least a 10% increase since that would be a common range of voltage variations.
Consider a buck-boost transformer with a 240 volt winding (maybe in the form of a pair of 120 volt windings configured in series) and a 32 volt winding (maybe in the form of a pair of 16 volt windings configured in series) where the 240 volt winding and 32 volt winding are in series. That would be a design voltage of 272 volts. Now if you connect a 277 volt supply circuit across the whole 272 effective winding (ungrounded on the 32 volt end, and grounded on the240 volt end), you would get around 244.5 volts across the 240 volt winding. How close is this getting to saturation? I calculate that 10% over 272 volts works out to right around 8% of the 277 volts. If the 277 volt supply does go up to 10%, how much saturation could be taking place?
What is the typical "percentage of voltage" before saturation begins to happen for this class of transformer? My understanding of saturation is that it is a gradual thing. But I've never studied it in particular, and some googling has not yet come up with any good material (except maybe a couple papers I cannot get more than a short abstract for at IEEE). But saturation theory is not the whole story, anyway, since it also matters how the transformer is designed.
I have seen brief voltage swells, usually 1/2 second to no more than 3 or 4 seconds, on the utility power, that are above 140 volts. If transformers are designed with a tight saturation tolerance, such swells could push them into the beginning saturation range.
Is such a bucking configuration a viable way to derive around 240 volts from around 277 volts? If not, I would have figured there would be transformers (of the autotransformer design) marketed specifically for dropping 277 volts to 240 volts.