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Discussion Starter · #1 ·
We are currently commissioning a conveyor system.

the system has about 20 fractional horsepower motors at 600v.

the first conveyor is the shortest, and so far, has several days worth of run time on site, and several days of run time at the shop.

This morning, the VFD faulted, overload. the motor was running at double the name plate amps. There was no obvious mechanical problem with the conveyor.

motor was isolated from the gearbox and still drew twice fla
motor was wired to a different VFD and still drew twice fla
a known good motor was wired to original VFD that had the bad motor and it ran at nameplate fla no problem

New spare motor was brought in from the shop. It was installed, turned on and within seconds it was up at double nameplate amps, exactly the same as the first. Isolated from gearbox, run on a different vfd, same result.

both motors fla were 0.8 amps and both motors drew 1.8amps

pulled the motors and isolated the wiring. Meggered out the windings and they were fine, but 1 set of windings on both motors (the same winding on both) was showing half the resistance as the other two windings. 20ohms vs 40 for the other two.

I have 2 more motors coming in tomorrow


interestingly, the motors were within 20 digits on their serial numbers.

I am going to bring the megger to site and check the cable, which is about 100 feet of 14/4 + aux VFD tray cable run in a enclosed wire mesh cable tray

but i dont see how the cable could be damaged and allow the motor to run

motor was not single phasing



any thoughts/suggestions?
 

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Are the motor settings in the VFD correct for the motor, primarily the frequency settings?

Are the motor internal leads connected for the proper voltage?

Overloads can be caused by the acceleration or deceleration settings. Have any of those settings been changed?

I would verify the motors are wired properly.
 

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We are currently commissioning a conveyor system.

the system has about 20 fractional horsepower motors at 600v.

the first conveyor is the shortest, and so far, has several days worth of run time on site, and several days of run time at the shop.

This morning, the VFD faulted, overload. the motor was running at double the name plate amps. There was no obvious mechanical problem with the conveyor.

motor was isolated from the gearbox and still drew twice fla
motor was wired to a different VFD and still drew twice fla
a known good motor was wired to original VFD that had the bad motor and it ran at nameplate fla no problem

New spare motor was brought in from the shop. It was installed, turned on and within seconds it was up at double nameplate amps, exactly the same as the first. Isolated from gearbox, run on a different vfd, same result.

both motors fla were 0.8 amps and both motors drew 1.8amps

pulled the motors and isolated the wiring. Meggered out the windings and they were fine, but 1 set of windings on both motors (the same winding on both) was showing half the resistance as the other two windings. 20ohms vs 40 for the other two.

I have 2 more motors coming in tomorrow


interestingly, the motors were within 20 digits on their serial numbers.

I am going to bring the megger to site and check the cable, which is about 100 feet of 14/4 + aux VFD tray cable run in a enclosed wire mesh cable tray

but i dont see how the cable could be damaged and allow the motor to run

motor was not single phasing



any thoughts/suggestions?
The different winding resistances are very suspicious. Are you sure these are 3-phase motors?
 

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Are the motor settings in the VFD correct for the motor, primarily the frequency settings?

Are the motor internal leads connected for the proper voltage?

Overloads can be caused by the acceleration or deceleration settings. Have any of those settings been changed?

I would verify the motors are wired properly.
Joined late, but instantly what I though. I see similar current draw issues all the time when newbies get something like a SEW gear motor pre-wired for a different voltage than supplied.

Sent from my SM-S908U using Tapatalk
 

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Can you post the motor tag and a photo of the strap connections? With the current doubling, sounds as if the motors are straped for the lower voltage. Causing the motor iron into severe magnetic saturation. If both motors megged at above 20M ohm, they should run fine if connected properly. The other site motor that you connected to check the VFD output, and it ran fine, may have the connection straps not exactly the same, compare them closely, there could be a terminal differences between motors.

You could also test the two suspected bad motors, by directly connecting them across the line voltage, and checking the current draw. That could rule out the VFD and the cabling as being part of the problem or not. I would also think that if the VFD was programmed properly, that at twice the FLA current that the drive should shut itself down promptly. 600V is pretty unforgiving as to a miswired motor, so check carefully before energizing.
 

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Discussion Starter · #10 ·
The different winding resistances are very suspicious. Are you sure these are 3-phase motors?
The different resistance readings is presumably because those windings have a short in them.

As for everyone's suggestions, all of these things have been checked. Last thing is to megger out the cable which I'm not sure how it would cause windings to short out.
 

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My facility rarely buys inverter duty motors for any conveyor. I do when they burn up when we are forced to run them at 20hz 19hrs a day. Not being inverter duty does not technically mean a drive can't run it.

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Discussion Starter · #14 ·
Incidentally, Nord came back with the specs and they are inverter duty.

This is a conveyor system part of a complete packaging system and none of the conveyors are running at 60hz. I'm not sure what happens to voltage when you alter Hz, and in turn the amplitude of the spikes.
 

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Incidentally, Nord came back with the specs and they are inverter duty.

This is a conveyor system part of a complete packaging system and none of the conveyors are running at 60hz. I'm not sure what happens to voltage when you alter Hz, and in turn the amplitude of the spikes.
lower hz also means lower volts, by how much is determined by how the drive is built and controlled
 

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Lower hertz can also means lower fan cooling. Then you Fukushima a motor.

Sent from my SM-S908U using Tapatalk
When I used to take service calls I'd open up a peckerchead and dramatically waft my hand towards my face. Look at my apprentice and say
"Smells like money."

He didn't last long, but never did he ask what I meant. I still to this day use that line sometimes when I open a smoked motor. Without the dramatic waft gig of course.

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Small random wound motors are pretty susceptible to punch thru on the windings with drives on longer runs. It often happens quick too.

I'd think it be real easy to be push IEC motors over their peak withstand limits on a 600 volt drive.
 
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