Configure Variable Torque VFD to run a Constant Torque Motor
Configure Variable Torque VFD to run a Constant Torque Motor
(OP)
I designed an MCC panel which has this 75hp VFD (Normal Duty) and after getting an Overload fault on the VFD, it just dawned on me that the application needs constant torque.
What can I do to salvage this situation before giving up and replacing the VFD? If let's say I decide to operate the VFD to run on a relatively narrow frequency band (between 40Hz to 55Hz), can I boost the torque in this range to be 60% of max torque at 40Hz and 90% of max torque at 55Hz? Can I do this buy manually setting the V/F ratio across 5 different frequencies?
Or is there any other setting that can be changed? I have a Schneider ATV630 VFD.
I will be trying a bunch of stuff tomorrow, but with the unreal lead times on any parts I even lay my eyes on, this truly is a bad time to make mistakes on sizing a VFD. Which I have managed to do. Any help will be greatly appreciated! And I am looking forward to getting educated here. Thanks!
What can I do to salvage this situation before giving up and replacing the VFD? If let's say I decide to operate the VFD to run on a relatively narrow frequency band (between 40Hz to 55Hz), can I boost the torque in this range to be 60% of max torque at 40Hz and 90% of max torque at 55Hz? Can I do this buy manually setting the V/F ratio across 5 different frequencies?
Or is there any other setting that can be changed? I have a Schneider ATV630 VFD.
I will be trying a bunch of stuff tomorrow, but with the unreal lead times on any parts I even lay my eyes on, this truly is a bad time to make mistakes on sizing a VFD. Which I have managed to do. Any help will be greatly appreciated! And I am looking forward to getting educated here. Thanks!
RE: Configure Variable Torque VFD to run a Constant Torque Motor
The constant and variable torque ratings are kind of stupid these days, the reality is that any new constant torque VFD is just an oversized variable torque VFD so it can provide a higher current above FLA longer. So, more overload torque.
RE: Configure Variable Torque VFD to run a Constant Torque Motor
By the default, the Motor Control type was on VC Quad. And the VFD would fault out after running for a few hours.
RE: Configure Variable Torque VFD to run a Constant Torque Motor
RE: Configure Variable Torque VFD to run a Constant Torque Motor
RE: Configure Variable Torque VFD to run a Constant Torque Motor
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RE: Configure Variable Torque VFD to run a Constant Torque Motor
RE: Configure Variable Torque VFD to run a Constant Torque Motor
RE: Configure Variable Torque VFD to run a Constant Torque Motor
In doing the changes for a VT load, the VFD will often ALSO have a different V/Hz output "curve" (as opposed to a fixed V/Hz ratio) because the load does not NEED as much torque as it slows down, so the VFD can reduce some losses in the motor by reducing the excitation current. That is done by enabling a "V/Hz2" output curve. If your VFD was configured like that, then applied to a Constant Torque load, you can indeed cause the drive to trip on MOTOR overload because it is EXPECTING much less from the motor. Whether or not your VFD can be re-programmed for a constant V/Hz pattern is going to be specific to your VFD, I don't like the Schneider drives (the manual sucks in my opinion), so I can't help you there, but MOST of the major player VFDs will have the ability to change that. What might happen though is that the internal programming for the VFD may then lower the maximum amp setting you can enter for the motor. Some do, some don't.
This would potentially solve the MOTOR overload issue, but will NOT change the VFD's capacity for running a CT load. That however is all going to be dependent on the ACTUAL LOAD on the motor (and thus the VFD) in your machine. So for example if you have a 75HP motor that is only running at 82A at full speed, and the VT rated drive is rated for 96A, then the OL capacity of the VFD is 110% of 96A, so 105.6A, which is going to give you 129% current capability for that load.
" 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: Configure Variable Torque VFD to run a Constant Torque Motor
This was the question about the torque load on the motor and a VT rated VFD which should be capable of this torque.
RE: Configure Variable Torque VFD to run a Constant Torque Motor
@LionelHutz If I set the VFD to Constant Torque settings (DRT - Heavy Duty), then it de-rates the Motor HP to 60HP (Motor I have is 75hp).
@jraek I cant say that I completely understand what you said, but it looks like VFD behaved exactly the way you described (V/Hz^2 output curve). I also made sure that the VFD does not operate below 40Hz because the motor nameplate says 2:1 CT. Which I understand is its way of saying "at lower Hz, the motor needs 50% no matter what". Is this correct?
RE: Configure Variable Torque VFD to run a Constant Torque Motor
" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden