VFD Driven Helper Motor?
VFD Driven Helper Motor?
(OP)
Background:
We have a 3500HP extruder motor that has been re-rated with a 1.40 service factor. The stator windings run cool, but is rotor limited beyond 1.40 loading.
A project is coming along to marginally increase the rates this machine must run. 10% increase in loading is expected after the project.
Management wants to couple a 350HP motor to the non-drive end of the 3500HP motor (this motor has a shaft extension on the NDE) fed from a VFD to boost HP of the application.
Question:
Is this possible from a purely technical standpoint?
The VFD would be set to run at a fixed speed around 70Hz (60Hz mains) with a current/torque limitation set to 100%. There would be no deceleration requirement for the VFD; it would always try to accelerate to an impossible speed target given the torque limitation constraint. I know the VFD can catch an already spinning motor and accelerate it. The 3500HP motor would already be running and fully loaded before running the VFD.
Management justification is that the 350HP motor and VFD is << than new a 5000HP motor and starter from a cost perspective.
Any input is welcome and appreciated. I know this is not an ideal setup. This is a cost saving measure to keep production in North America.
We have a 3500HP extruder motor that has been re-rated with a 1.40 service factor. The stator windings run cool, but is rotor limited beyond 1.40 loading.
A project is coming along to marginally increase the rates this machine must run. 10% increase in loading is expected after the project.
Management wants to couple a 350HP motor to the non-drive end of the 3500HP motor (this motor has a shaft extension on the NDE) fed from a VFD to boost HP of the application.
Question:
Is this possible from a purely technical standpoint?
The VFD would be set to run at a fixed speed around 70Hz (60Hz mains) with a current/torque limitation set to 100%. There would be no deceleration requirement for the VFD; it would always try to accelerate to an impossible speed target given the torque limitation constraint. I know the VFD can catch an already spinning motor and accelerate it. The 3500HP motor would already be running and fully loaded before running the VFD.
Management justification is that the 350HP motor and VFD is << than new a 5000HP motor and starter from a cost perspective.
Any input is welcome and appreciated. I know this is not an ideal setup. This is a cost saving measure to keep production in North America.





RE: VFD Driven Helper Motor?
RE: VFD Driven Helper Motor?
It sounds like a great idea and could probably be used to increase the life of the big motor on lower loadings.
What about using the 350 as a starter motor for the big one? Big one on a VFD?
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: VFD Driven Helper Motor?
And in the immortal words of E.L. Fudge, "Fudgeless is not a good thing and negative fudge is just a fudging disaster waiting to happen".
JRaef.com
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: VFD Driven Helper Motor?
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: VFD Driven Helper Motor?
There is no VFD on the 3500HP motor. The 350HP motor will not have enough starting torque to move the load.
The 3500HP motor has a breakdown torque of 260%. I should not even start to use any fudge until this point. Even with the helper motor at full load, this is 150% net loading on the 3500HP motor.
RE: VFD Driven Helper Motor?
If the %torque/speed curves of the motors are not a good match into the moderate overload range, forget this idea.
respectfully
RE: VFD Driven Helper Motor?
RE: VFD Driven Helper Motor?
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...