VFD limitation
VFD limitation
(OP)
Sirs
I have heard from some designers that Tmax/Tnom must be limited at 1,8 times if motors are driven by GFS in order to get stable operation.
Is this true?
If yes, why?
Thanks
I have heard from some designers that Tmax/Tnom must be limited at 1,8 times if motors are driven by GFS in order to get stable operation.
Is this true?
If yes, why?
Thanks





RE: VFD limitation
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: VFD limitation
The max torque that can be produces is the torque you get when you reach the rated maximum current of the VFD. In other words, start at rated current and full speed on the speed vs torque/current curves and slide back in speed until you reach rated VFD current. Then, pick the torque from the torque curve at this speed and that is max motor torque possible with that VFD. Try to pull more torque and the VFD will either trip on over current or it will begin to current limit (and torque).
RE: VFD limitation
You should program the drive to limit current or torque or both right at peak or slightly below peak or you could get the above mentioned stalling.
For NEMA B motors, this peak is usually about 2.2 times nominal.
RE: VFD limitation
My point is that you very likely can not install a drive that matches the motor size and get the breakdown torque from the motor. The maximum torque will be limited by the drive. Oversize the drive and you can get up to the breakdown torque, well close to it anyways.