VFD burning winding out on motor

clank

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Join Date
Jan 2005
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Ontario
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We installed 4 new conveyors. All 4 have new 1.5 Hp motors and all 4 have new Powerflex 40 VFD's (22B E3PON104). After 24 hours running one of the motors windings shorts to 1.6 ohms (normal 6.2). We changed motor and checked current and all was ok. Not a big load on conveyors anyways running way under FLA. After 24 hours the same conveyor motor had an short in winding again to 1.6 ohms. Checked all wiring with megger and all ok. My question is could the new VFD be causing motor issue and if so how as I never ran across this....or any other thoughts
Thanks
 
What is the operating voltage? How many wire feet between the drive and the motor? What is the insulation class of the motor? Does the motor have an MG1 Part 31 endorsement?

All of these matter a lot in determining your problem
 
45 feet between motor and drive....575 volts.....ins F . I have 3 others identical motors and drives with no issues....one is the same distance and other 2 are 63 feet
 
I seems very unlikely that two motors would fail in the same way in such a short time. I suggest you get you A-B distributor involved and replace that drive. If the problem goes away then A-B owes you a new drive and two motors.
 
When motor died the 2nd time....I needed to get conveyor running and I found a 460 volt that I could use, so I also changed drive to 460 volt model and has been running for 36 hours...
 
It doesnt explain why the 1st motor blew.
But using a motor with a lower rated voltage, it is not enough to specify the lower voltage in the regular setup of the VFD, when the VFD is rated for a higher voltage. The motor will experience the full voltage from the DC stage, even if the RMS value is much less. In the VFDs I have seen so far, you can manually set the DC stage voltage lower, and I guess that you should do that for a 460V motor on a 575V VFD.
At least that is what I have noticed for the VFDs that I have worked with (PF70, and MM440). The DC stage voltage wasnt intelligently reduced when inputting motor data for a lower voltage motor. Maybe newer VFDs are smarter than that.
 
Last edited:
I shorted out 2 575v motors using the new 575 VFD....I had no 575 volt motors in stock but found a 460 volt one I could use...I did not want to use the 575 VFD and dial it down to 460v....so I also changed the VFD....so back to original question, could the VFD damage the motors and how because I never came across that before
Thanks
 
If the motors were from the same lot and manufactured at the same time It is conceivable that it was a manufacturing defect. I have had instances in the past where several of the same items all had the same issue.
 
I suspect that, at 575V, smaller hp motors will need a load reactor at these distances.

I would add a 3% load reactor in each of the motor leads. It's good insurance.

The fact that the motor failures were shorted turns rather than short to ground makes PWM pulse insulation damage even more likely.

While I personally don't have much experience at 600V, I frequently read standards that recommend load reactors on virtually all motors on VFD's at that voltage.
 
I skimmed the PF40 manual, and couldnt find anywhere to set the DC bus voltage directly.
But parameter P042 "Voltage class" selects either "Low voltage (480V)" or "High Voltage (600V)". I suspect that this sets the DC bus voltage. The drive is set to High Voltage 600V as default.

edit: Typo "P040" instead of "P042".
 
Last edited:
DickDV
Thanks I will add reactors at later date but I did short windings of motor 2 times with same VFD and I have 3 others that are running fine....same motors, same VFD's and installed the same time
thanks again
 
JesperMP said:
I skimmed the PF40 manual, and couldnt find anywhere to set the DC bus voltage directly.
But parameter P042 "Voltage class" selects either "Low voltage (480V)" or "High Voltage (600V)". I suspect that this sets the DC bus voltage. The drive is set to High Voltage 600V as default.

edit: Typo "P040" instead of "P042".
Click to expand...

I would more suspect it doesn't control DC bus voltage, rather it dictates fault levels. The DC bus voltage level is going to be proportional to incoming voltage. The VFD needs to be told where its level is expected to be for fault and control reasons.

Please correct me if I am wrong. Note that the output current waveform and average voltage for the motor data can be simulated from either DC Bus level, but the drive needs to know where this should be. Some drives have more freedom of programming for minimum and maximum fault levels, but I have not seen one with a widley adjustable level you can set with a program.
 
OkiePC said:
The DC bus voltage level is going to be proportional to incoming voltage.
Click to expand...
That would be so if the DC bus voltage is generated by a simple bridge rectifier stage. But today they have more advanced rectifiers with choppers that can freely generate any DC voltage up to close to the incoming peak AC value.

On some VFDs I have seen, you can manually specify the DC bus voltage.
 
I have not seen a VFD that "controls" the Bus voltage. You have charging circuits that bring it up slowly and dumping circuits that "waste" the energy across a resistor if the Bus gets too high but nothing that actually regulates the Bus. Which isn't to say it could not be done, or even that it isn't done. The cost's likely outweight any benefit.

I think it also boils down to the consequence of failure as well. If a semi-conductor bridge is the only means you are using to "reduce" the mains then if it fails it may very well pass the mains voltage and create safety issues.
 
JesperMP said:
That would be so if the DC bus voltage is generated by a simple bridge rectifier stage. But today they have more advanced rectifiers with choppers that can freely generate any DC voltage up to close to the incoming peak AC value.

On some VFDs I have seen, you can manually specify the DC bus voltage.
Click to expand...


Jesper, you have peaked my curiosity. Can you reference an example VFD that does this?
 

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