>> We tested some small transformers in this role a few years ago.
>> They worked fine(ish) at 230V but we needed to go as high as
>> 270 or 280. At this voltage they started to saturate and the
>> output waveform became very distorted

> I'm more concerned about safety/reliability at the moment. As
> long as the tx keeps going (in a repeatable way across all units)
> it wouldn't be too hard to characterise the DC output of a full
> bridge against input AC. Assuming that the AC input could go
> as high as 280 at times, adding a series component could obviate
> saturation if necessary

It's necessary. Once you are saturating the waveform is non-sinusoidal 
(as yours was) and it would be extremely difficult to determine input 
voltage accurately. A series resistor is probably the nicest solution 
as it is well defined and less liable to have interesting interactions 
with the transformer inductance compared to eg a capacitor.


        RM 

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