Power Flex 40 shows fault code 13, what should I be looking for?

Steve Bailey

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New machine commissioning with two Power Flex drives, one 3 HP, one 0.5 HP. The 0.5 HP works fine. The 3 HP powers up OK, but displays fault code 13 as soon as you try to run it. The Quick start booklet that came with the drive identifies code 13 as a ground fault. The same Power Flex connected to the other motor works OK. The machine's owner reported today:

If the motor is disconnected from the machine, laying on the floor, only the 3 power lines attached, it runs fine. Both jog and run modes.

Bolted to machine, no coupling attached, able to turn armature with fan freely, absolutely no internal interference, get fault code on VFD.

Again, laying on floor, but with ground wire run from motor case to machine, get same fault code.

Laying on floor, no ground wire, running, check for voltage between motor case and machine, read 164 VAC. ????????

Dissemble motor on bench, repeatedly, visually check for any damage to windings or anything unusual. Every thing appears perfect.

Is this motor toast?
 
When you say reading 164 from motor frame to machine, do you mean machine frame or machine power to motor frame.

Also, i dont suppose your customer has a spare motor they can swap out for a quick test.
 
I'm pretty sure Steve means machine frame. They're reading voltage from the motor housing to the machine ground.

They should probably do one last test to make sure it's not in the wiring TO the motor. Temporarily connect the motor to the drive with another chunk of cable (or even 3 separate wires) and measure the ground voltage again (carefully!). If it's still present, toss the motor. It's only a 3HP motor, so it's probably not worth the time to diagnose.

🍻

-Eric
 
I'm not at the shop right now. I'm passing along the text of an email the owner sent me. At this point I'm looking to compile a list of suggestions to pass along to him.

He does have another motor available to test. The last thing I checked on Friday before I left was to swap the leads from the half HP motor to the 3 HP drive and make sure the Power Flex could turn that motor with no fault code. I was thinking along the same lines as Eric about making sure the problem isn't in the wires from the drive to the motor. I don't expect it is since the the wires are just running through about 6 feet of Sealtite from the enclosure to the motor, but it's an easy enough check.
 
Steve, I second Eric's idea on verifing wiring.
I had a PF40 that kept giving me ground faults same test as your except we changed a motor. Tested iton the floor, megged in the machine and out. It was a bad cable.
 
Almost 100% chance the motor is bad. If this is a 460V drive/motor system, you must megger the motor at 1000V to evaluate the insulation. Meggering at 500V or less is not adequate on inverter-driven power.

Conventional motor tests can easily show good when the motor insulation is failing with the high frequency square pulses a drive produces. Any ringing or overshoot on the pulses due to motor lead length just makes it worse. The drive will find a failing motor before most tests will.
 
If the motor is disconnected from the machine, laying on the floor, only the 3 power lines attached, it runs fine. Both jog and run modes.

Laying on floor, no ground wire, running, check for voltage between motor case and machine, read 164 VAC. ????????


Is this motor toast?

I assume "3 power lines attached" mean 3 phase from distribution and not from VFD output ??
IF SO I wonder what the voltage reading from motor frame to ground was?

With motor fed from VFD and getting 164 VAC to ground sure sounds like bad motor to me.

We had a VFD indicate ground problem checked to ground with Fluke VOM (yes I know that is not correct instrument but all I had) all read good. Let sit in shop for couple days and dry out (we assumed that is what cured the problem). Put back in operation with no problems after that.

This post has been quite informative to me. Thank you

Dan Bentler
 
Almost 100% chance the motor is bad. If this is a 460V drive/motor system, you must megger the motor at 1000V to evaluate the insulation. Meggering at 500V or less is not adequate on inverter-driven power.

Conventional motor tests can easily show good when the motor insulation is failing with the high frequency square pulses a drive produces. Any ringing or overshoot on the pulses due to motor lead length just makes it worse. The drive will find a failing motor before most tests will.

Dick

Does this mean that the test voltage should always be doubled when megging a motor that will connect to a vfd?

500 volts test voltage is ok for testing motors used in ATL motor control correct?
 
Dan,

No, what he did was to remove the motor from the machine and set it on the floor. The motor was still wired to the output terminals of the the VFD, but since it was not physically attached to the machine frame it was no longer grounded.
 
Dan,

No, what he did was to remove the motor from the machine and set it on the floor. The motor was still wired to the output terminals of the the VFD, but since it was not physically attached to the machine frame it was no longer grounded.

OK to clarify
so in both tests on floor it was powered by VFD?? Only difference between two tests was they measured frame volts to ground on second test??

Most educational - gonna have to remember this

Dan Bentler
 
OK to clarify
so in both tests on floor it was powered by VFD?? Only difference between two tests was they measured frame volts to ground on second test??

Most educational - gonna have to remember this

Dan Bentler

It sounds like the one test had the ground wore connected (this test had the fault occur) the second test was with the ground wire removed (this test did not have the fault occur)
 
The motor was always powered by the VFD. Whenever the motor frame is grounded, either by bolting it to the machine frame or by connecting s ground wire, the VFD shows a fault code 13 when it receives a run command.

Ungrounded, he sees a 164 volt potential between the motor frame and ground. I expect that is when the motor is running, It's a 230 volt motor and the speed pot is probably set at something less than 100%.
 
With the motor mounted to the frame and the ground wire connected to the motor, use a 1000V megger and test the insulation from where they are removed from the VFD, all the way through the motor. I normally clamp all three motor leads in the ground clamp at once and then touch the probe on ground before activating the megger. If there's a disconnect/terminal box/other terminations involved, you will be proving them all at one time, preferably before disturbing them. I have seen disconnects with ground faults that go away when you jiggle the handle, or open the box, and then return in the middle of production.

You need at least 2 megohms for a PF4 or 40 in v/hz mode, but I have seen some drives tolerate less, while others like some Toshiba G7s I have, that want over 100megohms to avoid tripping for ground faults.

I suspect you will read much less and find a damaged wire or motor winding. If you get a low reading, leave those wires off the drive, separate them from the motor leads and repeat the test.

The wiring, open at both ends, should read infinity or as near as your meter can to that, and the motor should read above 2 megohms.

The VFD is trying to protect you from a serious shock hazard. There is dangerous potential reaching the case of the motor, I would be 80% sure it's in the motor, at least inside the peckerhead, but prove it with a megger to be sure, and test the motor leads while you have the tools out.

DON'T apply 1000v meg test to wiring that is connected to the VFD.

It is remotely possible that the tech is seeing a carrier frequency induced voltage when the ground is removed, but the fact that the drive sees a ground fault...most likely the drive is right.
 
Last edited:
Way back when when ships were of wood and manned by men of iron the Navy taught me to never NEVER meggar any solid state.

I am sure Okie knows it but I think he would agree that instead of doing that caution in the last sentance his first should have read
Disconnect the VFD output conductors before doing any meggaring on motor supply conductors or motor.

Otherwise I agree with all else.

Dan Bentler
 

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