Running Hammer mill at 60 hz

[Whit7777]

We have a VFD on a 200-hp hammer mill (HM; milling wood chips). Motor: 3-ph/60 hz/1790 rpm/219 FLA/96.2 efficiency.
The mill is designed to run at 1790 rpm (issues if rpm slows down to much with hammers rocking on the pins, etc). Thus, I am pretty sure my PLC guy should set the VFD to run at 60 hz (currently set at 55 hz; which I think = about 1640 rpm, correct?) and then set our infeed conveyors to slow down
when HM amps spike above 210 for more than 2-3 seconds. Since this is a guess (both max amps and seconds above those amps), I'm seeking input/suggestions.

Our over-arching best-case scenario that we try to accomplish (never happens; just a goal) is for the infeed to be constant (material dropping off a conveyor into the HM at a steady rate), which would result in the HM running at a constant amperage; That would be too easy. Thus, since this can't happen, we intrinsically have amp-spikes that we have to accommodate. Just trying to figure out best way to go about handling this to maximize motor life, reduce total energy, etc.

Thanks.

 

[Little Bill]

Only advise we can give is to have your electrician work with your PLC guy on this as we can't help with those not in the electrical industry.
Thread closed.

 

[Jraef]

I opened this thread just to add this:

If your motor must run at full speed, get rid of the VFD as it has no purpose and is costing you around 3% of your power use, maybe more depending on how old it is. VFDs do not magically save energy on everything they are connected to. They only save energy on centrifugal pumps and fans. This hammer mill should have never had one if that was the goal.