Save money with VFD / Soft starter but caution about harmonics

The refinery I am working is fairly optimized in the energy department, so most of the transversal measures were already implemented. We already have capacitors in the general low tension switchboard, there are variable frequency drives or soft starters in almost every major motor, the lighting system was already retrofitted.

My overall facility distortion is below 5%. I am going to add VFDs to the remaining pumps in which the load fluctuates a bit, there are few of those. Soft Starters in a few motors over 20 HP. I am also lowering the frequency of 7 motors which led to a saving of 10000 euros/annually.

VFDs are notorious when it comes to adding harmonics to your system and capacitors can be good to increase PF but can also create a resonance in your system that can be incredibly detrimental to power quality. Your overall facility should be below 5% distortion on your voltage. If you look at the current distortion right at the variable frequency drive and motor it'll look a whole lot worse than it really is. Once the cumulative effect starts affecting your supply voltage (which is effecting everything else on the circuit) is when you need to start considering more options. As for < 10 HP motors having a 0.6 PF, do a simple economic study on the replacement cost of the motors for high efficiency motors. Make sure you take into account a demand charges or PF charges your utility might be assessing due to a low PF. Since you have so many it might be worth the cost.

The motors included in the sugar transport system work over 5000 hours a year, that is why I am considering in correcting the PF directly at the switchboard but like I already mentioned we already have capacitors installed in the general low tension switchboard.
I am currently starting to do the economic analysis of the proposals that I will present.