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Can I calculate the VFD energy savings?

I am of view that the variable frequency drive savings are rather application oriented. In constant torque applications like conveyors etc. the VFD savings as compared to DC drives are not great but savings are tremendously large compared to Eddy Current drives which now a days are rare to find. On the contrary, applications exhibiting centrifugal load characteristics yield tremendous savings depending upon normal running speed as a ratio to peak design speeds. Even one can expect to the tune of 65% to 70% depending upon empirical situations.

I also would like to share that in a centrifugal pump, if a outlet throttle control is employed for regulating flow - flow is proportional speed, head is proportional to square of the speed (although the head may not be required for the application) and power is proportional to cube of speed. If we replace the throttle control with a Variable Frequency Drive (VFD) and if the normal running speed is approx. 70% of full speed (possibly needed few times), the savings work out to 65%. Also by virtue of having controlled acceleration, the rating of drive mechanism (Motor with controls) can be optimized even for the high moment of inertia characteristics exhibited by the centrifugal load. This is another intangible saving as one can work at optimized loading pattern of motor. The VFD also poses a near unity power factor to the source.

It all depends on the application. I was just speaking in general not knowing the application you can NOT calculate the VFD savings rate.

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