I am designing an AC to DC converter. My power source is a single phase synchronous alternator that has a voltage range of 170~260 VAC and a frequency of 40~60 Hz. Can i use a transformer designed on 50 Hz and 220 VAC to work on my alternator specs mentioned above?
Can a 50 Hz, 220 VAC transformer work on 40 Hz, 180VAC?
Yes it probably can - the initial worry is saturation problems due to operating at the lower frequency but, with the voltage dropping to 180 V at 40 Hz, this produces virtually the same magnetization current as 220 V at 50 Hz.
Strictly speaking, if the transformer is nominally rated for 220 V at 50 Hz, you should run it at a nominal voltage of 176 V at 40 Hz.
Be on the safe side by using a transformer designed for heavier load. So the iron loss due to lower frequency can occupy the margin originally designed for heavier load (copper+iron) loss.
If you use the mentioned transformer, you will be running the risk that it will overheat when used at 260V, 40Hz. This is because your design requirements are "broader" than the capabilities of the suggested transformer.