Interesting question about the harmonics. Personally have doubts about any kind of harmonic filtration below 1 KHz for any passive technology, not including regeneration, but I'm not an expert and ferroresonance has it's mysteries. Don't have an oscilloscope to do any testing either.
Shared this link before with the caveats of the author affiliation and date.
http://www.contractorsav.com/article/2006/11/07/ac-power
Shared this link before with the caveats of the author affiliation and date.
http://www.contractorsav.com/article/2006/11/07/ac-power