Robicon VFD trips on under voltage 1

[jerrycamp]

I am working with an old Robicon VFD, model 422, installed around 1981. It powers a 40 hp GE motor. Instabilities in incoming power cause it to trip on under voltage. Under voltage condition lasts less than a second and is back up to rated. Vendor manual indicates board PC1 has this circuitry. In researching board schematics it does not appear that there are any delays or adjustments possible. Does anyone have any experience with this type of drive? Any delay or adjustment possible on undervoltage trip circuit?- Thanks

 

[dpc]

I suspect you are stuck with what you see. Undervoltage tripping was a very common issue for this vintage drive.

Newer drives are somewhat better with undervoltage ride-through and automatic re-starting.

I'd say it was time to retire that 1981 VFD and see if Robicon (Siemens) wants to put it in their museum.

 

[magoo2]

I've run into that before with VFDs, both old and new. They frequently trip off when the utility switches their capacitors on. The solution was to install a choke in series with the drive.

 

[LionelHutz]

It's most likely that the capacitors are not running at their rated value any more and the DC buss has less capacity than when new. So, under voltage conditions that would ride through before may not be now.

 

[jraef]

I'm not sure of that vintage, but it also used to be that the control system had it's own separate hold-up caps. Since your drive seems to indicate that it has that feature, yet it is apparently not working, I would suspect the caps on that Power Loss Ride Through feature have deteriorated. That happens with caps. Many Robicon reps also do their own service work on LV drives, have you tried that route?

I agree though that it may be time to consider replacement. As LionelHutz suggested, the main power caps have deteriorated as well (likely). If that's the case then it may be worth getting the better performance and efficiency from a newer drive rather than costly repairs to that one.

Still, 27 years operation from a VFD is, in my experience, one for the record books! I would think it worthy of a write-up by Siemens / Robicon (in exchange for a small repair job?) and I'm sure they would be happy to hear from you.


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