PowerFlex 400 Will Not Come Up To Speed

Rob... said:

Has this motor been rewound rather than replaced?

Are you sure winding polarity is correct?

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I'm not completely sure on that, but I believe it to have been re-wound.

I cannot say for 100%, but I would say that I'm 98% sure the polarity is correct as the motor was replaced ~3 months ago, the old drive died ~1 month ago, and the replacement drive ran Ok for the month leading up to this situation.

milldrone said:

Are you measuring at the infeed to the VFD or at the motor leads?

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Motor Leads.

milldrone said:

Was the original motor a 3560 rpm unit?

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Yes, according to the prints.

milldrone said:

Not a good sign, I have had motors that smelled ok but would not run. But every motor that I had identified as burnt has failed.

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My thought as well, although it had been running at low speed for a bit, so can understand how it may have built up some heat (TEFC motor).

milldrone said:

What you are describing sounds like a "first turn short". See if you can find a motor shop with a surge tester. Your motor sounds like it's around 60 hp, can you round up a good motor somewhere in the 20 to 60 hp range and temporarily hook it to test (no mechanical load) the VFD?

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They were getting the original motor back from the motor shop today, and that's what I instructed them to do.

Phrog30 said:

I would set parameters to default and start over. Worth a shot, I've had this happen to me and it's an easy thing to try.

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That was done, and I verified all parameters.

PLC Pie Guy said:

I would quickly wire up another motor right at the drive to see if it will run it. Cut out the existing motor circuit and just prove that the drive will ramp on on any other motor/motor leads.
I had a similar situation a few weeks back with a powerflex70. Motor occasionally, but more often than not, would hang at 17HZ but draw big amperage, even tripped the shear pin fault a few times. It was when I decided to connect another motor at the drive when I noticed a terribly loose connection on two of the drives output terminals. The wires were barely in the terminals at all. Tightened, problem solved!
You are describing very similar symptoms to what my situation had.

Check connections, and motor lead!

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Good idea - they will be getting their original motor back from the motor shop today, and that is exactly what I instructed them to do.

And I did check connections, all were good.

Phil Buchanan said:

Sounds like a Turn to Turn fault or a broken rotor bar. You will need a motor circuit analysis tester and/or a surge tester to find it.

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JTCat said:

You need to do a surge test as well as perform a polarization index test on the motor. Also a dielectric absorption ratio test would be helpful. A spot check to ground only tells us that there's not a ground short. It doesn't tell us much about the integrity of the winding insulation.

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Definite possibility there. Unfortunately, we don not have the ability to performs those tests. Or at least I did not have that ability yesterday (I will double-check the tools and equipment we have here at the office).

We'll see what happens when they get the old motor back and try that one.

kamaroman68 said:

How is the motor wired? Delta or Wye? When using a vfd if i remember correctly it needs to be wired for Delta. Ive been in plants that had the motors connected in wye(start) configuration to a vfd and the motors were scorching hot and burnt out prematurely. Id probably start there especially since you said the drive behaved correctly with motor disconnected.

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Delta: (see page 8)https://www.baldorvip.com/servlet/productInfoPacket/EM4310T.pdf

Everyone: thanks for all the help with this - I have certainly never seen anything like this before.

Still waiting on a call-back from my drive rep to see what he has to say, but everything that I read and was told pointed toward it being a motor problem.

I replied with as much info as I could so that if someone down the line has a similar issue, then hopefully it speeds along their troubleshooting. Lord knows I use this site for that a ton, only right that I give back when and if I can.

I will report back when/if I hear what their results were with the motor they are getting back from the motor shop. Unfortunately, this was a new customer, so the lies a very real possibility that it is a one-off and we don't hear back from them again. But I'm hopeful...

Thanks again!!
- Jeff

Inside of the PF400 there are protection circuits that will override everything to keep current below what the drive can handle (assuming the rate of rise is slow enough). So the VFD is seeing a short in the motor circuit somewhere and is keeping the drive from being damaged. You might be only reading 60A, but that's an averaged value of the current through the DC bus. The protection circuits are on each individual phase and if one or two phases are seeing a high spike of current, they will act on it. Although they are acting on the microprocessor to limit the current, they are not interacting with the displayed current values, they are much much faster. So the drive is doing it's job, but unfortunately cannot differentiate for you where the problem lies, only that it is down stream of the drive load terminals somewhere. Could be in the motor, could be in the conductors to the motor, terminal box, etc. etc. etc. If your new motor comes back from the shop and the problem remains, I would be looking at the other parts of the circuit.

JKS said:

Definite possibility there. Unfortunately, we don not have the ability to performs those tests. Or at least I did not have that ability yesterday (I will double-check the tools and equipment we have here at the office).

We'll see what happens when they get the old motor back and try that one.

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Most good motor shops have portable versions of these tools they can bring to your site to test large motors before they are removed, etc.

I have faced same problem and it turned out to be a cable issue, so disconnect the cable from the vfd and megger both the cable and the motor while is connected, at the end of the test make sure to discharge the cable.

good luck

Try meggeering at 2000V. Iv seen 1000V motor megger tests pass but fault ground on a drive!

you can check the motor leads from the drive to the disconnect pretty easy.

Usually any disconnect has an aux contact that forces you to have the disconnect closed so your not accidently have an open or someone opens the disconnect and the vfd would fault if the aux was not tied back to disable the vfd.

But bypass the disconnect aux, open the disconnect and turn the drive on. See if you have the same issue.

I had an issue with a new disconnect on an install that I thought was the motor but turned out to be an issue with the disconnect.

Maybe your drive is not rated for the motor? Even though the HP matches, maybe try the next size drive to see if it will run the motor better? Or you may have mechanical issue causing your motor to significantly wear faster than usual??

I'm wondering if he ever got this sorted out....

I'm curious as to what he found to be the smoking gun!

PLC Pie Guy said:

I'm wondering if he ever got this sorted out....

I'm curious as to what he found to be the smoking gun!

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As am I - I have not yet heard anything else from them.

I'll see if I can get a follow up and report back.