AB PowerFlex VFDs

Hi All,

We have an application like, a conveyor carrying load (raw materials) to a crusher. The conveyor's(motor's) speed is controlled by Powerflex70 VFD.

I'm not a VFD expert...

The problem is, as the load(weight) in the crusher is uneven, for higher loads
the conveyor's motor tries to maintain the pre-set speed thus increases the current which results in tripping.

Basic question is, is it possible to reduce the speed of conveyor's motor in accordance with load using VFD (without PLC)?

You may want to try "Droop". Go to page 3-29 of the manual for par.152.
Select how many rpm you want the drive to slow down at full load.
Maybe start a 50rpm..then bump up if needed.

There also should be a parameter that allows the drive to dynamically adjust the current limit. This approach might be a bandaid, and it might make things worse.

If the conveyor slows down, won't that increase the "pounds per foot" of material dumped on the conveyor exacerbating the problem?

If the drive is faulting for motor overload, then the motor may be undersized. If the drive trips with a different fault code please tell us exactly what the fault is.

With any VFD one of the most basic checks is to ensure that the FLA setting matches the motor nameplate. In some cases, I have had success raising that setting slightly to deal with intermittent overloads. This puts the motor at risk, but you have to weigh that risk against the value of production.


Paul

The short answer is "Yes", just set the drive current limit a couple of amps below the drive overcurrent fault level. When the current rises to the current limit level, the drive starts reducing the speed reference until the overcurrent goes away.

A better answer actually starts with a question: Why is the system seeing these overcurrent conditions? And then, is the mechanical part of the conveyor being overstressed? Where is the motor when this happens? Since we haven't been told what kind of fault occurs, the drive may simply be trying to protect the motor from overheating. Or, the drive may have been sized too small and is faulting on overcurrent to protect itself.

What I am trying to do here is encourage you to study this situation in more detail. You can make the tripping go away but that may only lead to other worse problems.