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Beware Of Line-Current Unbalance On VFDs

Find more articles on: Variable Frequency Drives

Jan. 1, 1999 John A. DeDad | Electrical Construction and Maintenance
Severe line-current unbalance can cause VFD nuisance tripping and 3rd harmonic currents, which are unusual for phase-to-phase nonlinear loads.Are you having problems with a "temperamental" variable frequency drive (VFD)? Is it nuisance-tripping, showing all the signs of circuit overload, even though measurements show otherwise? The culprit may be unbalanced phase currents.What happens is the overload

Discuss this Article 2

Christian (not verified)
on Mar 19, 2013

I've read that unbalanced current has a great effect on VFD's.
Can you help me with these problem. We have a three capactor banks rated 328 kvac per capacitor. These were used to supply out production plant. When we tried to close cap 1 together with cap 3 one of the cut out fuse exploded, which results to an unbalance current. The problem is that most of the VFD driven motors on our production tripped. Can these be attributed to the unbalance current of our capacitor bank?

Hope you could help me with these...

Thank you.

Stephen Woodworth (not verified)
on Apr 18, 2013

Our problem only occurs when we close the breaker to the circuit with the drive. Readings for the other 3-phase circuits without drives do not exhibit the same current imbalance. I suspect something was installed improperly, but have not personally witnessed the problem. Unfortunately, the site is half way around the world.

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