VFD size - motor size
VFD size - motor size
(OP)
Dear all,
as a rule of thumb we have always kept the VFD size (in kW) two times the motor size.
Now we have a project where a 0.37 kW three-phase motor is to be driven by a 1.5 kW VFD - this is because of delivery times,
we can't have a 0.55 kW in time for the job. Any suggestions? Do we have to put an inductor on the load side?
Thank you
as a rule of thumb we have always kept the VFD size (in kW) two times the motor size.
Now we have a project where a 0.37 kW three-phase motor is to be driven by a 1.5 kW VFD - this is because of delivery times,
we can't have a 0.55 kW in time for the job. Any suggestions? Do we have to put an inductor on the load side?
Thank you
RE: VFD size - motor size
RE: VFD size - motor size
Keith Cress
kcress - http://www.flaminsystems.com
RE: VFD size - motor size
RE: VFD size - motor size
RE: VFD size - motor size
I never oversize a drive unless I'm trying to play single phase source games. Most drives these days seem to have plenty of headroom when sized correctly. Often the drive's FLA rating is way above the drives rated hp anyway so there's no need to go up in drive sizes.
Keith Cress
kcress - http://www.flaminsystems.com
RE: VFD size - motor size
MOST drive mfrs will tell you not to use a drive at more than a 2:1 ration to the motor FLA, ie the drive is 2x the motor nameplate FLA. But as Keith pointed out, this is due to the vector control requirements. If you are using it strictly in V/Hz (scalar) mode, it’s relatively unimportant, especially on low cost small drives. In V/Hz mode the only thing the current sensors have to do is protect the motor from overload.
There are a few “next-gen” drives that are now using a form of Rogowski Coil for current measurement that can maintain accuracy down to a 10:1 size ratio, but they are not the low cost versions.
But I am curious why you ROUTINELY double the size of the drive? I’m sure the drive suppliers love you but it seems like a waste of money.
" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden
RE: VFD size - motor size
normally we use same size as the motor. Or we pickup the next size available. As you pointed out there is current enough.
RE: VFD size - motor size
" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden