Active Front End (AFE) VFD vs. 12-Pulse VFD

[Jraef]

Not necessarily so.
We did quite a few paoer mills with 12 and 24 pulse systems. The largest, as I recall, is a 4MVA system with 17 variable speed drives. The drives were a mixture of DC, DC 4-quad and some variable frequency inverters.
The system comprised two 2MVA 11kV/520V transformers, four six pulse plain rectifiers, and a 700Vdc busbar distribution system with all the drives hanging off that.

Lowest order harmonic is 23rd and, as you know, harmonic amplitude is roughly proportional to the reciprocal of the harmonic number. The arrangement has benefits on system efficiency but that's another story for another day.

Another excellent approach, but one that takes a fairly talented engineer such as yourself available to make that happen. Not everyone has a resource like that available and has to rely on vendors and COTS solutions.

 

[Jraef]

CB tripping may be a result of the GF protection picking up. Remember HF signal sees capacitance to ground as low impedance.

And if those breakers don't have GF protection built in, it could also the result of severe line transients causing the drives to draw very high peak currents. These are typically too fast for a breaker to react to, but the combined effect might be cumulative to the point of causing instantaneous trips. That could potentially be mitigated by simply adding line reactors (assuming there are none).

The main point however is that solving the harmonics issue, although gaining other benefits, may not necessarily solve the breaker tripping issue of it has not been properly vetted. I know that was someone else's job, not yours, but I would forewarn the owner of the possibility of that recurring after they spend all that money. If it were me, I'd do a little more snooping and I would probably add line reactors anyway first. Even if they later want to change out to newer drives for other reasons, the reactors would still be a good idea for those too and would be left in place for that retrofit.