Intermittant Drive trips

[JesperMP]

I tried something similar:
Disable the drive, and wait to open the contactor at the moment the drive signalled "stopped", but even that generated the overvoltage alarm. I had to wait an additional fraction of a second to not have the alarm. Not knowing if this was only a nuisance or a severe danger to the drive I decided to put the contactor on the inlet side (better safe than sorry).
It was an AB PF70 if it makes any difference.

 

[tom_stalcup]

Just my own two cents... The last time I had a problem like this, one of the other maintenance techs had replaced the freq drive(ge) and the new freq drive didn't come pre-configured with a braking resistor. Anytime the drive tried to decel at too high a rate, the drive would trip out. It took us a little while to track it down because we weren't sure if it was a drive problem, or a problem with the brake on the motor not actuating properly. The original drive had a resistor mounted(internally) so we didn't think to check for that at first.

 

[Thomas Sullens]

You might check with your power supplier. If they have capacitors on their primary lines that step cap. in and out automatically.This can cause your problem.

 

[Jim in NH]

I am coming to this discussion late, as I have just found this site, but maybe can still help? It wans't clear whether the problem has ever been satisfactorily resolved.

Three reasons for OV trips have been mentioned - 1) too short a deceleration rate and 2) extenal influence from a grounded system pushing voltage up on the DC bus and 3) high line voltage. The first is unlikely here (though easy to check -- double the decel time as someone above has said, though this will have the effect of dampening the response of the system). The second is, in my opinion, the more likely here. The third is normally the fault of the utility, and can be monitored.

I will finish in a second message, as I will run over-length if I finish here.

 

[Jim in NH]

more on overvoltage

Some VFD's have a capacitor coupling from the DC bus to earth ground as part of the RFI ckt. If connected to an electrical supply with an intentionally grounded leg (grounded Delta power) it will trip on OV, but this would happen immediately and every time you powered up the VFDs. If there is an intermittent ground fault problem in the plant (maybe caused by some other machinery), you can get this problem intermittently. If there is an RFI jumper, pull it. Or, install a D-Y drive isolation xformer (DIT), giving the drive the wye side and not bonding the center tap to the service ground. Check your service by measuring voltage phase to ground.

You might be experiencing a high line condition on one or more legs. We once had a problem at the utility substation with a voltage regulator. Or, you might see higher voltage in the early AM or on third shift, when there is less load - a line reactor will mitigate, but not solve this problem.