Grounding of motor nuetral for VFD application
Grounding of motor nuetral for VFD application
(OP)
We presently have a 200 Hp ,460 volt motor connected in wye which is provided power from a SquareD VFD controller.We typically always bring motor leads together and connect them to ground but Square D has some concerns that this will cause problems with their VFD drive. Is this reasonable to leave the motor nuetral leads ungrounded
"floating" in this application.
"floating" in this application.





RE: Grounding of motor nuetral for VFD application
I don't see any technical reason that letting it float would be a problem -- and I would generally defer to the VFD vendor.....
RE: Grounding of motor nuetral for VFD application
I have seen that habit carried over to other motor control applications where no grounding shall be done.
Never ground any neutral or star point when running off a VFD!
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Grounding of motor nuetral for VFD application
I'm going to knock off for the rest of the day now, I have learned my new thing.
RE: Grounding of motor nuetral for VFD application
You must be very confident that the supply voltages will always be exactly equal and the phase angles will always be exactly equal.
A three phase induction motor will try to balance unequal supply voltages. That is part of the reason that a motor heats up if the supply voltages are unequal.
If the neutral is connected then the motor will also try to correct unequal phase angles. The motor may also see greater voltage unbalances phase to neutral than phase to phase.
Don't ground the motor neutral unless a specific drive specifically requires it.
By the way, if single phase voltage regulators are used on the distribution circuits in your area, you may see fairly good phase to neutral voltages, but unequal phase to phase voltages and phase angle errors.
Bill
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"Why not the best?"
Jimmy Carter
RE: Grounding of motor nuetral for VFD application
RE: Grounding of motor nuetral for VFD application
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Grounding of motor nuetral for VFD application
RE: Grounding of motor nuetral for VFD application
The leads that form the star point on the low voltage connection are at about 139 volts on the igh voltage connection. You probably are right about the star/delta configuration jraef.
Bill
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"Why not the best?"
Jimmy Carter
RE: Grounding of motor nuetral for VFD application
Definite No for VFD
Roy
RE: Grounding of motor nuetral for VFD application
But those were voltage controllers based on triacs - no VFDs.
Grounding the star point of a VFD fed motor would probably create a DC path from mains via DC link rectifiers, IGBTs and motor winding to ground. That would not be good at all.
So, as already said, don't do it.
Still very interested to know from where hydropowerengr got this idea. Hello hydropowerengr! Any answer to that?
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Grounding of motor nuetral for VFD application
Connecting the Y point to neutral could be considered OK code wise but is almost never done in practice.
RE: Grounding of motor nuetral for VFD application