overvoltage fault on vfd

From experience, I had a Siemens G20 VFD running an older 7.5 HP non-inverter rated motor. We got random F2 (Overvoltage) faults, to such an annoying degree that we created a 2x fault reset routine. A few months in, the motor packed it in. I'm betting that our motor was weak, and that the stresses of the VFD (High DC Bus spikes on the windings) caused it to fault the drive occasionally, why it registered as over voltage I'm not sure, but it definitely only happened when the drive was stopping. We put a new motor on there, and haven't had a single fault since.
 
This is a brand new motor. Customer informed me today that it seems to be when the motor goes from under load to no load, for example, when the blade exits the log. That would fit with your regen idea, right? Is a line reactor going to be the best solution? What about a dc reactor or choke?
 
This is a brand new motor. Customer informed me today that it seems to be when the motor goes from under load to no load, for example, when the blade exits the log. That would fit with your regen idea, right? Is a line reactor going to be the best solution? What about a dc reactor or choke?

I am late to the party, but that sounds like it might call for a dynamic brake resistor module to be added.
 
The thing about adding the braking resistor is that it will not really "care" why the OV situation happens, it will just take care of it. That's what I would do too. Just keep an eye on it because if the problem is continuous, the brake resistor may not be able to handle it. From the sounds of it, that's not the case.
 
It's regen. Get a DB and you will be happy. Your Motor/VFD are probably a little undersized for the application (common for high inertia band saws) which makes matters worse.

I have also seen poor motor grounds cause this. Once had a client with the same issue. Completely random. After a lot of field work we discovered that the motor Ground Terminal was sitting on paint and was not grounding motor well. When a Motor is not grounded well (especially with belt drives) the motor effectively "charges" its self and upon discharged will sometimes cause drive to trip. Not a common problem but happens.

https://www.controleng.com/single-a...to-know/f9c4ae94ed0d2381cf95ed2b914a6fd8.html
 
One late thought on this. Since this is reported to only occur when going from load to no-load, the problem may be caused by the speed loop being tuned up a little too hot. Reducing the P gain or the I time a bit might end the faulting, as well.

Of course, if the VFD is configured open loop V/Hz, the above would not apply.

I agree that a brake resistor would likely fix the problem, whatever the cause.
 

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