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Old November 25th, 2018, 12:00 PM   #1
MHennel
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PowerFlex 525 Problem

I have a system that has about 40 PowerFlex 525 VFD's on it. They are all running conveyor belts, not a difficult application. Most are 1HP Motors. I have one of them that that on occasion will loose the at reference signal back to the PLC (Over Ethernet). When trending the at reference signal and the output frequency signals from the VFD, I loose the at reference signal for a second or so when the out frequency jumps from 60 to 61HZ for a short instance. The VFD is set to run at 60HZ. I have never noticed and issue like this before. I don't understand why the VFD output frequency occasional jumps to 61HZ. It is set to a max frequency of 60HZ.


Has anyone run into something like this before. it is only happening on one VFD and it is a small belt with very little drag on it.
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Old November 26th, 2018, 07:49 AM   #2
kekrahulik
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I'm guessing you are running in SVC mode?

The drive tries to keep the motor running at 60Hz. If the drive THINKS the motor speed is sagging a little, the drive will increase the frequency (to 61 or so) to pickup the motor speed. During this time, the at reference signal will be lost. For that reason, I am very careful to when using the at reference signal.

If you place the drive in V/Hz mode, I doubt you will see this because the drive would then output 60Hz without any extra correction for control. The motor will also running closer to it's nameplate full speed.

So why has it changed? Maybe the mechanical load has changed or something is binding a bit? The drive uses the output current and voltage to make it's decisions, so you may want to verify your wiring connections. Maybe something in the motor? I don't think you are in danger of something imminently dying, but if it hasn't acted this way before, some thing has changed.
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Old November 26th, 2018, 11:54 AM   #3
MHennel
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Thanks for the suggestions I will give them a try.
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Old November 28th, 2018, 10:33 AM   #4
jraef
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I’ve seen this happen when you are in SVC and did not perform an autotune procedure. That’s how it gets the wrong info from the motor feedback, it’s not comparing it to the right model.

I ran into this once and the engineer insisted they had done the autotune because it showed in the records. Turned out some hotshot technician on the night shift played around with the programming, then got himself lost and reset to factory defaults, which lost the motor model. I’ve also seen it where someone changes the motor, not knowing that the new motor requires that the drive be tuned to it.

Last edited by jraef; November 28th, 2018 at 10:44 AM.
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Old November 28th, 2018, 12:52 PM   #5
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Quote:
Originally Posted by jraef View Post
Iíve also seen it where someone changes the motor, not knowing that the new motor requires that the drive be tuned to it.

Had this happen to me recently, after we autotuned the original motor, we discovered it had a bad bearing and had it replaced. We didn't think to do a new autotune and the motor wasn't operating correctly, but that went away as soon as we autotuned the drive with the new motor. Nice when the problem is that simple for a change!
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Old November 28th, 2018, 01:54 PM   #6
sbaum
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This doesn't really apply to the OP's application, but I actually just had a incident this morning where I learned a few extra details about the PF525.

Was doing a new startup of a small decanter (high interia load). The current was oscillating while ramping and when at full speed. I was also seeing the frequency jump above 60hz as the OP described. This was happening on both SVC and V/Hz modes. I typically set up centrifuges to use scalar modes because speed controllers in most of the drives I've used have difficulty with the high interia of a centrifuge. But in this case the V/Hz mode was acting the same.

Put a call in to AB Tech Support. Stumped the first guy and he got an engineer on the line for me. We ended up setting P036 Motor NP RPM to sychronous speed and it fixed the problem. He said doing that disables the Slip Compensation in V/Hz mode.
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Old November 28th, 2018, 02:19 PM   #7
mylespetro
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Originally Posted by sbaum View Post
Put a call in to AB Tech Support. Stumped the first guy and he got an engineer on the line for me. We ended up setting P036 Motor NP RPM to sychronous speed and it fixed the problem. He said doing that disables the Slip Compensation in V/Hz mode.

That's a good one to have in your back pocket. I can't wait to forget about that when the time comes
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