Power flex drive operating above speed reference.

[einnh]

What could cause a drive to output above set point speed reference while in flux vector and speed control? Drive in question is attached to a winder. Speed reference and set point are 25Hz but sometimes the drive under medium load will operate at about 50Hz saying its current limited. The system has a braking resistor sizes for 100% OHL.

 

[califflash]

Could you provide some more information? What's the cat number of the drive? Is this pure sensor less vector with a speed command. Or is there a torque feedback or dancer involved?

 

[jraef]

And could it be, since it's a winder, that the load is PULLING it at a higher speed and despite it TRYING to brake, it is current limiting into the brake, which is not allowing enough braking torque to prevent the overhaul?

 

[rdrast]

What does the actual drive show for its final speed reference an feedback? (Diagnostic parameters).

 

[ASF]

And could it be, since it's a winder, that the load is PULLING it at a higher speed and despite it TRYING to brake, it is current limiting into the brake, which is not allowing enough braking torque to prevent the overhaul?

I'd say jraef is on the money. Seen something similar before on a paper machine where a DC drive wasn't controlling the tension properly - we took the terminal cover off and monitored the voltage; all present and correct, but still behaving badly. We were just about to shut down the plant and change out the motor (and it was a big one) when someone twigged - the inverter had a blown field fuse, the motor wasn't being driven at all. It was being towed, and acting as a generator.

(and just to explain why we didn't pick it up straight away by looking at the inverter for a fault code - this wasn't actually an off the shelf DC drive, it was a component-level built monstrosity from the 40's. No smarts at all to that thing!)

 

[einnh]

Its a 43A PowerFlex 755 Drive. on a 400V system.

The current setup is in the forward (pay out) direction the drive operates in mode 1 (speed regulator), in reverse direction (haul in) the drive operates in SLAT MAX (mode 4).

Winder paying out always has a set point speed lower than the one paying in. Current limit is currently set to 64.5A.

The haul-in winder is only operating at -30% torque (FV mode). I would assume the pay-out winder is not hitting it's current limit but would have to monitor.

 

[AutomationCtrl]

If the speed ref on the drive is lower than the speed feedback which seems to be the case from your description, then I second jraef's observation.

Is the current limit the only message you see when the problem occurs, no other trip conditions in the history?

Is it actually braking? Not familiar with the powerflex drives, some drives have a torque reading you can get from the drive. A negative reading would show if the drive 'thinks' its in a regenerative quadrant and needs to engage the brakes. Otherwise, it has essentially lost the load electrically.

 

[leighigh]

I would look at the minimum speed setting first. make sure it is not set above the speed you want it to run at.

 

[einnh]

The brake is currently sized for 100% OHL for the drive selected (based on PowerOHM's recommendation). Should we go with an even higher rating?

 

[kamenges]

Is your bus regulation mode parameter set to dynamic braking? It almost sounds like it is attempting flux braking. One of the things I personally like to do is to set the bus regulation mode to dynamic braking only if I have a braking resistor available. I would rather have the drive fault on an overvoltage so I know what I am dealing with than to modify the torque capacity out from under me.

Keith

 

[Gene Bond]

Sounds like its in bus regulation mode to me... Seen a few runaways here and there