i know of three ways a transformer can saturate, one is by feeding it a primary voltage it was not intended for, say a 110volt fed of the 220 volt source, or simply overloading the secondary, drawing more current than what it was designed for, the third would be if you operate the ransformer at much lower frequency it was designed for, example, a 400hz transformer fed off a 60hz source.
since most designs operate at about just below the knee of the magnetization curve, to get good regulation with less copper, staying well within the design parameters can keep you out of trouble.
this is a 600VA isolation transformer i made for my pc's line filter, it had a 1.75 in core stacked 3inches, it had equal turns of ga#16 with 350turns each.
