Thanks you.
I can relate to what u are saying because at a point we used a higher rated vfd (“5.5 kW”both Omron and Toshiba) to run the motors separately (each motor 0.5 kW) and they operated quite fine for a long while.
Eventually we lost their IGBTs along the line. The problem still persisted.
I’d really appreciate it if u could help me get the application note u are talking about. I believe it can help.

The problem may indeed be high voltage spikes that arc from the rotor to the field coils. In some motor applications with some kinds of non-conductive load, such as a belt, somehow a static charge builds up on the rotor. The solution is a rotor grounding device that keeps the rotor connected to the motor frame. The problem is common enough that products to do this are available. And who would ever guess that was the source of the high voltage?

 

I had an old vfd blow fuses at inconvenient times, until I installed an input choke that alleviated that problem.

Are you braking these motors?

No I’m not braking them

 

No I’m not braking them

An input choke makes sense, but also consider grounding the motor rotors.
What is the motor load?? Does it drive a belt??

 

An input choke makes sense, but also consider grounding the motor rotors.
What is the motor load?? Does it drive a belt??

Its a 500 W vibrating motor, it doesn't drive a belt. It transfers its vibration to a post that in turn vibrates a bed of screens (kind of a mesh) to sieve out particular sizes of material.

 

Another thought on your problem. Do your wires run in Liquatite or Sealtite? If not fine carbon dust could be getting into the motor "peckerhead" and shorting them out from time to time. It just seems very unusual for so many VFD's going bad the same way.



You have to forgive bill, he starts reading in the middle or end of a thread.

 

Another thought on your problem. Do your wires run in Liquatite or Sealtite? If not fine carbon dust could be getting into the motor "peckerhead" and shorting them out from time to time.

Good call, I've never seen that happen, but also I've never seen VFDs drop like flies as has been described here. It should be obvious if this has been happening, when you open the peckerhead you should see arc marks. But, maybe it is never opened. Maybe megger checks have been performed from inside the MCC. if so, the shorts would have probably disappeared each time the VFD blew up, carbon dust and transistors being vaporized at the same time. And subsequent megger check performed from MCC shows all good.

 

Have you tried running the motors without load for a test?
Have you tried a auto-tune on them? Or at least set the parameters correctly?
What kind of wiring between VFD & motor? VFD shielded or conduit with discrete conductors?

Looks like auto tuning seems to have solved the problem

thnx.

 

Looks like auto tuning seems to have solved the problem

thnx.

Well that's amazing! Borderline unbelievable even. Thanks for coming back to give closure!

 

Well that's amazing! Borderline unbelievable even. Thanks for coming back to give closure!

Yeah unbelievable.
I really appreciate all the help from everyone.
Thanks once again.