Application is a dust collector. Motor ran fine for a couple years, then they added some additional duct work and motors started burning out after only a few days use. Culprit appears to be excessive current draw. At 30 Hz the 25 hp motor is pulling 40A where it's nameplate FLA is 29A. I went through the standard troubleshooting checklist looking for shaft mis-alignment, bad bearings, un-grounded shield, proper wire configuration for the voltage. I started to focus on the V/Hz setting in the VFD then stumbled upon old threads with discussion about blowers without any back pressure pulling the motor all the way down the fan curve to the point of failure. Just today the client informed me that with the discharge of the blower blocked 50% they had favorable current draw.
Isn't there a way to set up the VFD to handle an open discharge configuration? That is, solve this electrically rather than mechanically?
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