einnh
Lifetime Supporting Member
I am curious what your take is on sizing VFD's for variable torque applications. In the past I have sized for ND amp ratings paired with the motor (talking PowerFlex) drives but we have started running into limitations on performance so we talked with our VAR and they recommended in the future going to HD rated drives (basically for Rockwell this means the next size up drive).
I spoke with TechConnect the other day about this same issue and their recommendation was to size it so the software current limit could be set at 200% of the motor FLA. On the ND drives I know the current limit seamed to max out at 150% or 165%, I'm not sure about the HD rated drives. But If I use this sizing method the drive is basically 2 sizes larger than the ND rating (amp output). Is that really necessary? It seems excessive, especially if sizing conductors and other components to match the ratings; getting increasingly more expensive on the larger hp drives.
Another thing to take into account is I have been sizing my motors to handle 110% of the load the process guys hand me which has their own safety factor built in.
Thanks,
Eric
I spoke with TechConnect the other day about this same issue and their recommendation was to size it so the software current limit could be set at 200% of the motor FLA. On the ND drives I know the current limit seamed to max out at 150% or 165%, I'm not sure about the HD rated drives. But If I use this sizing method the drive is basically 2 sizes larger than the ND rating (amp output). Is that really necessary? It seems excessive, especially if sizing conductors and other components to match the ratings; getting increasingly more expensive on the larger hp drives.
Another thing to take into account is I have been sizing my motors to handle 110% of the load the process guys hand me which has their own safety factor built in.
Thanks,
Eric