Is that where those AEGIS rings come in?
Helwig Carbon - the "old line" brush maker - are one of several who have bolt-on solutions. Check it out online. Also tons of "white papers" out there, many with specialty camera photos of corona in action and bearings that have been damaged.
Machine-tool precision spindle bearings - SG's high on the list - should NOT be so casually treated. Too DAMNED expensive to replace, basically.
For the cost, methinks it make far more sense to stay with pure-sine wave power sources to begin with, rather than monkey-patch older motors around modern VFD's rudeness.
Now.. any RPC so qualifies.
It offers-up a certain amount of rude behaviour UP the line - utility-(local)-grid-side
(see "THD", and how it might annoy your nearest residential neigbour on the same pole-pig or ground-vault transformer..).
Even so, any RPC's OUTPUT, or load, side is pure sine-wave, never, ever any fast-switching, fast-rise transients. So..even if.. one leg is not as 'stiff' as the other two, all that means to a 3-Phase motor as load is that it can only hit a max of 91% or so of "nameplate'.
For most of our use? "Bee Eff Dee". RPC's JFW.
I probably should buy a RPC...if the budget didnt go towards the grinder!
Two 10 HP Phase-perfects (one old "blue" bought used, one brand-new "white") and my more beloved of machines Dee Cee drive as well?
I still run a 10 HP RPC too! "Bullet proof" in way, they are.
"Half" home-built.
I bought a brand-new Weg (Brasil, not China) 10 HP 1750 RPM 3-Phase motor, under $400 shipped, and then - only AFTER I KNEW the RPM I'd be working with - ordered one of Jim's "Phase-Craft" - which is also his PM handle - RPC starter/Control boxes. I know how to build my own. I even have all the needed parts to build
several.
I have better things to do with my scarce time that try to catch-up to what Jim already knows - even just as to the "nuisance" diversion of DIY'ing or adapting a bleepin' enclosure, cutting and terminating wire, and mounting the darned parts!
Plenty of OTHER stuff I just HAVE TO "DIY", so... made more economic sense than might first appear to just go near-as-dammit "turnkey" on a mission-critical item of this sort.
An SG needs clean and very stable power. Take note, for example, that 1-P driven ones are notorious for fine "watermark" patterns on the ground surface from the ever-so-slight vibration at the wheel.
OTOH - SG's do not, hardly ever - mind the 9% or 10% drop from theoretical max HP of RPC vs "true" utility mains nor 4 LARGE-plus cost of a new Phase-Perfect.
And.. an RPC can drive all sorts of OTHER 3-Phase goods without the "reprogramming" recommended if one tries to use a VFD for more than a single matched and dedicated motor load.
RPC also last near-as-dammit forever, vs a VFD wanting replaced every several years because the new caps any reputable maker specs - right in the manual, read it and weep - usually cost more than a whole new VFD.
3CW