Powerflex 4

Any chance your motor is regenerative? Is this happening when you are stopping and there is some kind of momentum in your system? Overvoltage is frequently caused by the motor becoming a source (generator) rather than a load - and then you may need a dynamic braking resistor to get rid of the fault.

As mentioned above, overvoltage, is usually caused by the motor, becoming driven , like a generator, creating a regenerative voltage, adding to the existing voltage, hence the term overvoltage, you may need something done on the mechinical side in addition to possibly adding a braking unit, and/or brake resistors.

What size motor, and voltage??

example 480v 7.5hp 1800rpm motor, driving a belt conv.

Also is the motor directly coupled or does it have a gear reducer in between, belt drive, drive chain, mechinical direct drive coupling, fuild coupling, clutch ????

We need a few more details,

here is a link to the manual for the AB Powerflex 4M VFDs we use,

http://literature.rockwellautomation.com/idc/groups/literature/documents/um/22f-um001_-en-e.pdf

it will tell you everything you need to know about these VFDs, these are very easy drives to use, we have several smaller ones around the site on lube pumps, and mechinical actuators/rams.

Guys, notice he says that the drive returns to fault as soon as he resets it. Unlikely then that the motor is running or regenerating.

Check your input voltage to the drive. It's going to cause a High Voltage Fault if its above 506 volts. Even repetitive voltage pulses above that level with fault the drive.

And, meg-ohm the cables and motor...The PF4 can give you an overvoltage fault sometimes due to a phase to phase short...not sure why, I suspect long motor lead length may play a part, but I have seen it at least 3 times, as soon as you send a start command (not just reset).

If it faults just sitting there idle, then it is likely plant voltage spikes or just too high as already said.

Ran into this quite a bit.
Sometimes a line reactor on either the line or load side will take care of it but many times I had to replace the drive.

If it is in an enclosure change it to either a Powerflex 4M or a Powerflex 523.

DickDV said:

Guys, notice he says that the drive returns to fault as soon as he resets it. Unlikely then that the motor is running or regenerating.

Check your input voltage to the drive. It's going to cause a High Voltage Fault if its above 506 volts. Even repetitive voltage pulses above that level with fault the drive.

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I believe if this were the case, it would be more along the lines of DC Buss Overvoltage.

did you just recently install the VFD, or is it an existing unit that has ran for years.

If new install, typically you would install the line and load reactors, and limit the cable length to the specs in the manual.

Can you provide more detail to the actual problem, then , the drive faults on overvoltage.

mcantee45 said:

We are having troubles with our powerflex 4 drive showing an over voltage fault. If I could look at the parameters I would, but once you try and clear the fault it will appear almost instantly. We have checked the wiring to the drive and suspect either the drive or motor is going bad. Again I can't clear the fault at all to even try and change some settings. Any help would be useful. Thanks!

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Disconnect the motor, and power up the drive, see if the problem goes away. Let us know what you find.

There is no other form of "over voltage fault" other than DC bus over voltage.

The PF4 does not have as sophisticated of a set of protection features, it is an entry level drive. Therefore if there is excessive DC bus ripple, it trips on OV, it does not have a separate trip for "Excess DC bus ripple" as the Architecture class drives do. So if you have lost a phase, that can happen, but usually only under load. If it happens immediately like this, and you are ABSOLUTELY sure the line voltage is not high, it probably means you have lost one or more of the DC bus caps, which means the drive is toast and you need to replace it. It is not repairable, or rather it will cost you more to repair it than to replace it. Plus if the caps failed, a more devastating failure would be likely right after you did manage to replace them because whatever took them out must have been pretty bad.

By chance, was this drive sitting somewhere un-powered for a long time?

DickDV said:

...It's going to cause a High Voltage Fault if its above 506 volts.

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No, the trip threshold is equivalent to 290VAC for a 240V drive, 575VAC for a 480V drive.

Even repetitive voltage pulses above that level with fault the drive.

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That part is true. I'm trying to get the minimum time frame for the surge for someone else, I'll post it if I get it from Engineering, but my gut feel is that there is little or no delay in that trip function once the DC bus rises above the threshold. I have one right now that the pulses are too fast for a basic hand held multimeter to see, but a scope sees them if we turn the filter down. No idea yet where they are coming from, all I know is that they are there. In this case they do have a line reactor, but when the drive is powered up but off so there is no load, therefore almost no current through the reactor, the VD trough the reactor drops to nearly nothing and the spikes get through. People have a difficult time understanding that. Voltage drop through a reactor is related to current going through it, so when a drive is not running a motor, it does not help much with spikes.

jraef, are you saying that the DC bus in a PF4 is good up to 575 x 1.414 = 813vdc?

And regarding your comment about pulse suppression in an input reactor, since the inductance of the reactor doesn't change at any current less than saturation, why would there be any reduction in suppression at low current levels?

DickDV said:

jraef, are you saying that the DC bus in a PF4 is good up to 575 x 1.414 = 813vdc?

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810VDC, but yes.

And regarding your comment about pulse suppression in an input reactor, since the inductance of the reactor doesn't change at any current less than saturation, why would there be any reduction in suppression at low current levels?

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I wasn't referring to suppression, I was referring to voltage drop. People ASSUME that voltage drop through a rector is equivalent to the percent impedance of the reactor, ie 3% reactor = 3% voltage drop across it. I was simply pointing out that is not correct; V(across the inductor) = I * XL, so if I = zero, V-drop = 0. So installing a reactor ahead of a drive, while still SUPPRESSING dV/dt (the RATE of RISE of the voltage), will not really effect the actual total RMS voltage getting to the drive terminals if the motor is not running and there is no current flowing through the reactor.

Side note: I checked in on whether or not there is a "dwell" time on the OV trip threshold, the answer was what I expected, no. So even a brief spike that results in a DC bus voltage over 810V will cause the drive to trip on OV, or put the way they said it; "The over Voltage Trip is enacted immediately the moment the DC bus voltage goes from 809.99VDC to 810.00VDC".

OK, I"m with you on that reactor stuff. I thought you were referring to suppression.