VFD troubleshooting

[unsaint33]

Our fan VFD keeps faulting out about every hour. To rule out a bad motor, I disconnected the motor wires from the VFD. After that, the VFD runs good all day (no more faults). Is that a reliable way to determine a bad motor or bad VFD?

 

[ck8177]

By itself, not necessarily. Can you provide more details?

What type of drive? AB Powerflex? SEW? Automation Direct? Etc.

Is there a fault code on the drive when the fault occurs? What is the fault code? Is it the same fault code every time the fault occurs?

Does this fan run continuously for the full hour between faults?

Regardless, I would definitely check resistance on the motor using a multimeter or Megger with the motor disconnected from the drive. I would also take current readings on each phase of the motor during normal operation (some VFDs will provide you with this data in the motor parameters).

This would help eliminate the motor as a potential issue. I wouldn't rule out the VFD without more information/testing. I have seen VFDs run flawlessly with no load, just as you have described, only to fail under load due to faulty internals.

 

[unsaint33]

What type of drive? AB Powerflex? SEW? Automation Direct? Etc.

abb acs141-1k6-1

Is there a fault code on the drive when the fault occurs? What is the fault code? Is it the same fault code every time the fault occurs?

FL 4 * Fault current:
• Output ground fault (200 V units).
• Short circuit.
• Supply disturbances

The fact that the VFD ran all day when the motor was disconnected, the supply disturbances is not the issue.

Does this fan run continuously for the full hour between faults?

It varies but it ran up two an hour before fault out.

Regardless, I would definitely check resistance on the motor using a multimeter or Megger with the motor disconnected from the drive. I would also take current readings on each phase of the motor during normal operation (some VFDs will provide you with this data in the motor parameters).

Meggered the motor. No issue found.

We are ordering a VFD as a back up even if the VFD was not the culprit. Thank you for your reply.

 

[unsaint33]

What type of drive? AB Powerflex? SEW? Automation Direct? Etc.

abb acs141-1k6-1

Is there a fault code on the drive when the fault occurs? What is the fault code? Is it the same fault code every time the fault occurs?

FL 4 * Fault current:
• Output ground fault (200 V units).
• Short circuit.
• Supply disturbances

The fact that the VFD ran all day when the motor was disconnected, the supply disturbances is not the issue.

Does this fan run continuously for the full hour between faults?

It varies but it ran up to one hour before faulting out.

Regardless, I would definitely check resistance on the motor using a multimeter or Megger with the motor disconnected from the drive. I would also take current readings on each phase of the motor during normal operation (some VFDs will provide you with this data in the motor parameters).

Meggered the motor. No issue found.

We are ordering a VFD as a back up even if the VFD was not the culprit. Thank you for your reply.

 

[Steve Bailey]

My experience is that a VFD will generate fault due to a bad motor before a megger will detect it.
But the fact that it runs for an hour before generating the fault suggests something related to the load the motor sees.
If you can immediately restart the motor after it shuts down due to the code and get another hour of running, that suggests you are running slightly above current limit. If you have to wait before being able to restart, it suggests a wire being pinched as the motor heats up. Is the motor very hot after running for an hour?

 

[BryanG]

You seem to show that there are three faults covered by that code.
Don't ignore the Supply Disturbance - it could allow the drive to function without fault when the motor isn't connected because the supply will be affected by the power pulled by the VSD.

 

[alan_505]

What voltage did you megger the motor at as it needs to at least twice the nominal supply voltage.
The VSD will put out spikes higher than the nominal voltage, so if it is a 200v motor you need to test at least 500v if it is a 400v motor you need to test at least 1000v.

 

[ck8177]

You seem to show that there are three faults covered by that code.
Don't ignore the Supply Disturbance - it could allow the drive to function without fault when the motor isn't connected because the supply will be affected by the power pulled by the VSD.

Looking through the manual for this drive series, the three bullet points under the fault code in OP's reply look to be a list of potential causes of said fault.

Link: https://library.e.abb.com/public/5a6341a27dac0beec12571c40047e6f8/ACS140U_US_04_Web.pdf

It is worth noting that on this model VFD, output overcurrent appears to be a separate fault code which OP implies is not displayed. Makes me wonder if an intermittent short in the wiring may be the culprit.

 

[TWS]

Megger the motor supply leads. ( from the Drive to the motor.)
I you are not using shielded VFD cable, the insulation of conductors feeding the motor may be failing.
Check for moisture in the conduits feeding the motor. Check the supply feeds for loose connections, evidence of arcing ect.
I all that is OK then i would lean in the direction of "Supply Disturbances"

 

[jraef]

Our fan VFD keeps faulting out about every hour. To rule out a bad motor, I disconnected the motor wires from the VFD. After that, the VFD runs good all day (no more faults). Is that a reliable way to determine a bad motor or bad VFD?

If the motor is disconnected, you are not "running" the VFD, you are just energizing it... No load = no power flowing through the unit or wiring, so of course, no problems! If you have some other motor, even if not the same size, that you can connect to the drive unloaded, see if the problem persists with a load connected and running.

Is this a NEW installation or has it been running fine for a long time and just now exhibited this behavior? If it has been running fine and just started doing this, then I would suspect a motor issue issue first, then a wire issue, then a drive issue last.

If you eliminate the motor, wire and drive issues, then it's time to look at the process. On centrifugal fans, the LOAD = FLOW, so of the flow suddenly increases, then the drive will overload. That can happen on a fan system when someone inadvertently opens a damper or diverter so that suddenly there is no back pressure (static pressure) on the air flow system, so the fan attempts to deliver more air flow that the setting of the drive wants to allow. USUALLY that shows up as a "motor overload" fault, but sometimes it depends on how fast it happened and the OC fault triggers first.

 

[Dale87]

We fought one of these "only runs for a couple hours " situations one time on a 30hp Eaton DG1. We where getting a ground fault and overload fault. We megged the motor, and conductors, checked out connections on each end more times than I can count. Eaton said "run the drive unhooked" so we ran it that way for 24 hours no issue. Eaton said it had to be the motor or conductors. We didn't buy that, it was a brand new motor and install, and would run fine across the line. We tried everything, new VFD, new motor leads...... Finally we got a hold of the right guy at Eaton TRC, we where feeding the drive control board with 24vdc, so we could turn the 208v ac feed off to the drive in the off season, as the utility voltage in that particular area was prone to some wild voltage fluctuations and transients. But we didn't want our PLC to lose the IO connection via Ethernet to the drive. Eaton TRC guy says turn your 24vdc ps down to below 21, the problem will go away..... He was right....maybe not the same situation as mentioned here but with drives..... anything's possible.

 

[unsaint33]

Hi. Sorry for the late follow up. I wanted to get enough data... We ended up getting a new open box VFD of the same model. Transferred all parameters exactly the same to the new VFD, wired it up to the motor. That solved the problem. Never tripped any more. So it had to be the bad VFD then, right? Well, we brought the old VFD to the shop and wired it with another 208V motor with a slightly less HP. It never tripped all day long. So, I don't know what's going on.