Inverter Duty vs. Premium Efficiency

If you are using a VFD, use the inverter duty motor. Premium Efficiency motors mean nothing if the motor is not running full speed. If running full speed for any length of time (to where a percent or two difference in efficiency would make a difference), you should re-evaluate your need for a VFD. ANY motor application driven by a VFD will have decreased overall efficiency because the VFD has losses, so the only time you want to use a VFD is when speed control is absolutely beneficial and/or the use of the VFD decreases overal power consumption to begin with.

Thank you for the vindication.

The VFD's are required not only for energy savings but to maintain the facilities static pressure. I speced the job with the inverter rated motors due to energy loss and bearing loss due to electrical drainage from the stator to the motor ground through the motor bearings, which I have seen many times in the past.

The customer (who is always right) pushed back and said premium. The ROI's have changed due to the Drive amperage needed to keep the motor at proper speed. the premium seems to suck more from the capacitance buss than the inverter duty motors.

There are a lot of 18-pulse VFDs that can run a non-inverter duty motor without consequence. Even for those that are not configured to work with a Premium Efficiency motor, you can add a filter so that the motor is getting a clean sine wave. It will still run warmer at lower speeds, but it won't have the spikes that demand an inverter-duty motor.